Import SQLite 3.7.6.3.

third_party/sqlite/src/ext/fts3/fts3.c

 /*
 ** 2006 Oct 10
 **
 ** The author disclaims copyright to this source code.  In place of
 ** a legal notice, here is a blessing:
 **
 **    May you do good and not evil.
 **    May you find forgiveness for yourself and forgive others.
 **    May you share freely, never taking more than you give.
 **
 ******************************************************************************
 **
 ** This is an SQLite module implementing full-text search.
 */
 
 /*
 ** The code in this file is only compiled if:
 **
 **     * The FTS3 module is being built as an extension
 **       (in which case SQLITE_CORE is not defined), or
 **
 **     * The FTS3 module is being built into the core of
 **       SQLite (in which case SQLITE_ENABLE_FTS3 is defined).
 */
 
-/* TODO(shess) Consider exporting this comment to an HTML file or the
-** wiki.
-*/
 /* The full-text index is stored in a series of b+tree (-like)
 ** structures called segments which map terms to doclists.  The
 ** structures are like b+trees in layout, but are constructed from the
 ** bottom up in optimal fashion and are not updatable.  Since trees
 ** are built from the bottom up, things will be described from the
 ** bottom up.
 **
 **
 **** Varints ****
 ** The basic unit of encoding is a variable-length integer called a
 ** varint.  We encode variable-length integers in little-endian order
 ** using seven bits * per byte as follows:
 **
 ** KEY:
 **         A = 0xxxxxxx    7 bits of data and one flag bit
 **         B = 1xxxxxxx    7 bits of data and one flag bit
 **
 **  7 bits - A
 ** 14 bits - BA
 ** 21 bits - BBA
 ** and so on.
 **
-** This is identical to how sqlite encodes varints (see util.c).
+** This is similar in concept to how sqlite encodes "varints" but
+** the encoding is not the same.  SQLite varints are big-endian
+** are are limited to 9 bytes in length whereas FTS3 varints are
+** little-endian and can be up to 10 bytes in length (in theory).
+**
+** Example encodings:
+**
+**     1:    0x01
+**   127:    0x7f
+**   128:    0x81 0x00
 **
 **
 **** Document lists ****
 ** A doclist (document list) holds a docid-sorted list of hits for a
-** given term.  Doclists hold docids, and can optionally associate
-** token positions and offsets with docids.
+** given term.  Doclists hold docids and associated token positions.
+** A docid is the unique integer identifier for a single document.
+** A position is the index of a word within the document.  The first 
+** word of the document has a position of 0.
 **
-** A DL_POSITIONS_OFFSETS doclist is stored like this:
+** FTS3 used to optionally store character offsets using a compile-time
+** option.  But that functionality is no longer supported.
+**
+** A doclist is stored like this:
 **
 ** array {
 **   varint docid;
 **   array {                (position list for column 0)
-**     varint position;     (delta from previous position plus POS_BASE)
-**     varint startOffset;  (delta from previous startOffset)
-**     varint endOffset;    (delta from startOffset)
+**     varint position;     (2 more than the delta from previous position)
 **   }
 **   array {
 **     varint POS_COLUMN;   (marks start of position list for new column)
 **     varint column;       (index of new column)
 **     array {
-**       varint position;   (delta from previous position plus POS_BASE)
-**       varint startOffset;(delta from previous startOffset)
-**       varint endOffset;  (delta from startOffset)
+**       varint position;   (2 more than the delta from previous position)
 **     }
 **   }
 **   varint POS_END;        (marks end of positions for this document.
 ** }
 **
 ** Here, array { X } means zero or more occurrences of X, adjacent in
 ** memory.  A "position" is an index of a token in the token stream
-** generated by the tokenizer, while an "offset" is a byte offset,
-** both based at 0.  Note that POS_END and POS_COLUMN occur in the
-** same logical place as the position element, and act as sentinals
-** ending a position list array.
+** generated by the tokenizer. Note that POS_END and POS_COLUMN occur 
+** in the same logical place as the position element, and act as sentinals
+** ending a position list array.  POS_END is 0.  POS_COLUMN is 1.
+** The positions numbers are not stored literally but rather as two more
+** than the difference from the prior position, or the just the position plus
+** 2 for the first position.  Example:
 **
-** A DL_POSITIONS doclist omits the startOffset and endOffset
-** information.  A DL_DOCIDS doclist omits both the position and
-** offset information, becoming an array of varint-encoded docids.
+**   label:       A B C D E  F  G H   I  J K
+**   value:     123 5 9 1 1 14 35 0 234 72 0
 **
-** On-disk data is stored as type DL_DEFAULT, so we don't serialize
-** the type.  Due to how deletion is implemented in the segmentation
-** system, on-disk doclists MUST store at least positions.
+** The 123 value is the first docid.  For column zero in this document
+** there are two matches at positions 3 and 10 (5-2 and 9-2+3).  The 1
+** at D signals the start of a new column; the 1 at E indicates that the
+** new column is column number 1.  There are two positions at 12 and 45
+** (14-2 and 35-2+12).  The 0 at H indicate the end-of-document.  The
+** 234 at I is the next docid.  It has one position 72 (72-2) and then
+** terminates with the 0 at K.
 **
+** A "position-list" is the list of positions for multiple columns for
+** a single docid.  A "column-list" is the set of positions for a single
+** column.  Hence, a position-list consists of one or more column-lists,
+** a document record consists of a docid followed by a position-list and
+** a doclist consists of one or more document records.
+**
+** A bare doclist omits the position information, becoming an 
+** array of varint-encoded docids.
 **
 **** Segment leaf nodes ****
 ** Segment leaf nodes store terms and doclists, ordered by term.  Leaf
 ** nodes are written using LeafWriter, and read using LeafReader (to
 ** iterate through a single leaf node's data) and LeavesReader (to
 ** iterate through a segment's entire leaf layer).  Leaf nodes have
 ** the format:
 **
 ** varint iHeight;             (height from leaf level, always 0)
 ** varint nTerm;               (length of first term)
@@ skipping 167 matching lines @@
 ** into a single segment.
 */
 #define CHROMIUM_FTS3_CHANGES 1
 
 #if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3)
 
 #if defined(SQLITE_ENABLE_FTS3) && !defined(SQLITE_CORE)
 # define SQLITE_CORE 1
 #endif
 
+#include "fts3Int.h"
+
 #include <assert.h>
 #include <stdlib.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
-#include <ctype.h>
+#include <stdarg.h>
 
 #include "fts3.h"
-#include "fts3_expr.h"
-#include "fts3_hash.h"
-#include "fts3_tokenizer.h"
 #ifndef SQLITE_CORE 
 # include "sqlite3ext.h"
   SQLITE_EXTENSION_INIT1
 #endif
 
-
-/* TODO(shess) MAN, this thing needs some refactoring.  At minimum, it
-** would be nice to order the file better, perhaps something along the
-** lines of:
-**
-**  - utility functions
-**  - table setup functions
-**  - table update functions
-**  - table query functions
-**
-** Put the query functions last because they're likely to reference
-** typedefs or functions from the table update section.
+/* 
+** Write a 64-bit variable-length integer to memory starting at p[0].
+** The length of data written will be between 1 and FTS3_VARINT_MAX bytes.
+** The number of bytes written is returned.
 */
-
-#if 0
-# define FTSTRACE(A)  printf A; fflush(stdout)
-#else
-# define FTSTRACE(A)
-#endif
-
-#if 0
-/* Useful to set breakpoints. See main.c sqlite3Corrupt(). */
-static int fts3Corrupt(void){
-  return SQLITE_CORRUPT;
-}
-# define SQLITE_CORRUPT_BKPT fts3Corrupt()
-#else
-# define SQLITE_CORRUPT_BKPT SQLITE_CORRUPT
-#endif
-
-/* It is not safe to call isspace(), tolower(), or isalnum() on
-** hi-bit-set characters.  This is the same solution used in the
-** tokenizer.
-*/
-/* TODO(shess) The snippet-generation code should be using the
-** tokenizer-generated tokens rather than doing its own local
-** tokenization.
-*/
-/* TODO(shess) Is __isascii() a portable version of (c&0x80)==0? */
-static int safe_isspace(char c){
-  return (c&0x80)==0 ? isspace(c) : 0;
-}
-static int safe_tolower(char c){
-  return (c>='A' && c<='Z') ? (c-'A'+'a') : c;
-}
-static int safe_isalnum(char c){
-  return (c&0x80)==0 ? isalnum(c) : 0;
-}
-
-typedef enum DocListType {
-  DL_DOCIDS,              /* docids only */
-  DL_POSITIONS,           /* docids + positions */
-  DL_POSITIONS_OFFSETS    /* docids + positions + offsets */
-} DocListType;
-
-/*
-** By default, only positions and not offsets are stored in the doclists.
-** To change this so that offsets are stored too, compile with
-**
-**          -DDL_DEFAULT=DL_POSITIONS_OFFSETS
-**
-** If DL_DEFAULT is set to DL_DOCIDS, your table can only be inserted
-** into (no deletes or updates).
-*/
-#ifndef DL_DEFAULT
-# define DL_DEFAULT DL_POSITIONS
-#endif
-
-enum {
-  POS_END = 0,        /* end of this position list */
-  POS_COLUMN,         /* followed by new column number */
-  POS_BASE
-};
-
-/* MERGE_COUNT controls how often we merge segments (see comment at
-** top of file).
-*/
-#define MERGE_COUNT 16
-
-/* utility functions */
-
-/* CLEAR() and SCRAMBLE() abstract memset() on a pointer to a single
-** record to prevent errors of the form:
-**
-** my_function(SomeType *b){
-**   memset(b, '\0', sizeof(b));  // sizeof(b)!=sizeof(*b)
-** }
-*/
-/* TODO(shess) Obvious candidates for a header file. */
-#define CLEAR(b) memset(b, '\0', sizeof(*(b)))
-
-#ifndef NDEBUG
-#  define SCRAMBLE(b) memset(b, 0x55, sizeof(*(b)))
-#else
-#  define SCRAMBLE(b)
-#endif
-
-/* We may need up to VARINT_MAX bytes to store an encoded 64-bit integer. */
-#define VARINT_MAX 10
-
-/* Write a 64-bit variable-length integer to memory starting at p[0].
- * The length of data written will be between 1 and VARINT_MAX bytes.
- * The number of bytes written is returned. */
-static int fts3PutVarint(char *p, sqlite_int64 v){
+int sqlite3Fts3PutVarint(char *p, sqlite_int64 v){
   unsigned char *q = (unsigned char *) p;
   sqlite_uint64 vu = v;
   do{
     *q++ = (unsigned char) ((vu & 0x7f) | 0x80);
     vu >>= 7;
   }while( vu!=0 );
   q[-1] &= 0x7f;  /* turn off high bit in final byte */
-  assert( q - (unsigned char *)p <= VARINT_MAX );
+  assert( q - (unsigned char *)p <= FTS3_VARINT_MAX );
   return (int) (q - (unsigned char *)p);
 }
 
-/* Read a 64-bit variable-length integer from memory starting at p[0].
- * Return the number of bytes read, or 0 on error.
- * The value is stored in *v. */
-static int fts3GetVarintSafe(const char *p, sqlite_int64 *v, int max){
+/* 
+** Read a 64-bit variable-length integer from memory starting at p[0].
+** Return the number of bytes read, or 0 on error.
+** The value is stored in *v.
+*/
+int sqlite3Fts3GetVarint(const char *p, sqlite_int64 *v){
   const unsigned char *q = (const unsigned char *) p;
   sqlite_uint64 x = 0, y = 1;
-  if( max>VARINT_MAX ) max = VARINT_MAX;
-  while( max && (*q & 0x80) == 0x80 ){
-    max--;
+  while( (*q&0x80)==0x80 && q-(unsigned char *)p<FTS3_VARINT_MAX ){
     x += y * (*q++ & 0x7f);
     y <<= 7;
   }
-  if( !max ){
-    assert( 0 );
-    return 0;  /* tried to read too much; bad data */
-  }
   x += y * (*q++);
   *v = (sqlite_int64) x;
   return (int) (q - (unsigned char *)p);
 }
 
-static int fts3GetVarint(const char *p, sqlite_int64 *v){
-  return fts3GetVarintSafe(p, v, VARINT_MAX);
-}
-
-static int fts3GetVarint32Safe(const char *p, int *pi, int max){
+/*
+** Similar to sqlite3Fts3GetVarint(), except that the output is truncated to a
+** 32-bit integer before it is returned.
+*/
+int sqlite3Fts3GetVarint32(const char *p, int *pi){
  sqlite_int64 i;
- int ret = fts3GetVarintSafe(p, &i, max);
- if( !ret ) return ret;
+ int ret = sqlite3Fts3GetVarint(p, &i);
  *pi = (int) i;
- assert( *pi==i );
  return ret;
 }
 
-static int fts3GetVarint32(const char* p, int *pi){
-  return fts3GetVarint32Safe(p, pi, VARINT_MAX);
-}
-
-/*******************************************************************/
-/* DataBuffer is used to collect data into a buffer in piecemeal
-** fashion.  It implements the usual distinction between amount of
-** data currently stored (nData) and buffer capacity (nCapacity).
-**
-** dataBufferInit - create a buffer with given initial capacity.
-** dataBufferReset - forget buffer's data, retaining capacity.
-** dataBufferDestroy - free buffer's data.
-** dataBufferSwap - swap contents of two buffers.
-** dataBufferExpand - expand capacity without adding data.
-** dataBufferAppend - append data.
-** dataBufferAppend2 - append two pieces of data at once.
-** dataBufferReplace - replace buffer's data.
-*/
-typedef struct DataBuffer {
-  char *pData;          /* Pointer to malloc'ed buffer. */
-  int nCapacity;        /* Size of pData buffer. */
-  int nData;            /* End of data loaded into pData. */
-} DataBuffer;
-
-static void dataBufferInit(DataBuffer *pBuffer, int nCapacity){
-  assert( nCapacity>=0 );
-  pBuffer->nData = 0;
-  pBuffer->nCapacity = nCapacity;
-  pBuffer->pData = nCapacity==0 ? NULL : sqlite3_malloc(nCapacity);
-}
-static void dataBufferReset(DataBuffer *pBuffer){
-  pBuffer->nData = 0;
-}
-static void dataBufferDestroy(DataBuffer *pBuffer){
-  if( pBuffer->pData!=NULL ) sqlite3_free(pBuffer->pData);
-  SCRAMBLE(pBuffer);
-}
-static void dataBufferSwap(DataBuffer *pBuffer1, DataBuffer *pBuffer2){
-  DataBuffer tmp = *pBuffer1;
-  *pBuffer1 = *pBuffer2;
-  *pBuffer2 = tmp;
-}
-static void dataBufferExpand(DataBuffer *pBuffer, int nAddCapacity){
-  assert( nAddCapacity>0 );
-  /* TODO(shess) Consider expanding more aggressively.  Note that the
-  ** underlying malloc implementation may take care of such things for
-  ** us already.
-  */
-  if( pBuffer->nData+nAddCapacity>pBuffer->nCapacity ){
-    pBuffer->nCapacity = pBuffer->nData+nAddCapacity;
-    pBuffer->pData = sqlite3_realloc(pBuffer->pData, pBuffer->nCapacity);
-  }
-}
-static void dataBufferAppend(DataBuffer *pBuffer,
-                             const char *pSource, int nSource){
-  assert( nSource>0 && pSource!=NULL );
-  dataBufferExpand(pBuffer, nSource);
-  memcpy(pBuffer->pData+pBuffer->nData, pSource, nSource);
-  pBuffer->nData += nSource;
-}
-static void dataBufferAppend2(DataBuffer *pBuffer,
-                              const char *pSource1, int nSource1,
-                              const char *pSource2, int nSource2){
-  assert( nSource1>0 && pSource1!=NULL );
-  assert( nSource2>0 && pSource2!=NULL );
-  dataBufferExpand(pBuffer, nSource1+nSource2);
-  memcpy(pBuffer->pData+pBuffer->nData, pSource1, nSource1);
-  memcpy(pBuffer->pData+pBuffer->nData+nSource1, pSource2, nSource2);
-  pBuffer->nData += nSource1+nSource2;
-}
-static void dataBufferReplace(DataBuffer *pBuffer,
-                              const char *pSource, int nSource){
-  dataBufferReset(pBuffer);
-  dataBufferAppend(pBuffer, pSource, nSource);
-}
-
-/* StringBuffer is a null-terminated version of DataBuffer. */
-typedef struct StringBuffer {
-  DataBuffer b;            /* Includes null terminator. */
-} StringBuffer;
-
-static void initStringBuffer(StringBuffer *sb){
-  dataBufferInit(&sb->b, 100);
-  dataBufferReplace(&sb->b, "", 1);
-}
-static int stringBufferLength(StringBuffer *sb){
-  return sb->b.nData-1;
-}
-static char *stringBufferData(StringBuffer *sb){
-  return sb->b.pData;
-}
-static void stringBufferDestroy(StringBuffer *sb){
-  dataBufferDestroy(&sb->b);
-}
-
-static void nappend(StringBuffer *sb, const char *zFrom, int nFrom){
-  assert( sb->b.nData>0 );
-  if( nFrom>0 ){
-    sb->b.nData--;
-    dataBufferAppend2(&sb->b, zFrom, nFrom, "", 1);
-  }
-}
-static void append(StringBuffer *sb, const char *zFrom){
-  nappend(sb, zFrom, strlen(zFrom));
-}
-
-/* Append a list of strings separated by commas. */
-static void appendList(StringBuffer *sb, int nString, char **azString){
-  int i;
-  for(i=0; i<nString; ++i){
-    if( i>0 ) append(sb, ", ");
-    append(sb, azString[i]);
-  }
-}
-
-static int endsInWhiteSpace(StringBuffer *p){
-  return stringBufferLength(p)>0 &&
-    safe_isspace(stringBufferData(p)[stringBufferLength(p)-1]);
-}
-
-/* If the StringBuffer ends in something other than white space, add a
-** single space character to the end.
-*/
-static void appendWhiteSpace(StringBuffer *p){
-  if( stringBufferLength(p)==0 ) return;
-  if( !endsInWhiteSpace(p) ) append(p, " ");
-}
-
-/* Remove white space from the end of the StringBuffer */
-static void trimWhiteSpace(StringBuffer *p){
-  while( endsInWhiteSpace(p) ){
-    p->b.pData[--p->b.nData-1] = '\0';
-  }
-}
-
-/*******************************************************************/
-/* DLReader is used to read document elements from a doclist.  The
-** current docid is cached, so dlrDocid() is fast.  DLReader does not
-** own the doclist buffer.
-**
-** dlrAtEnd - true if there's no more data to read.
-** dlrDocid - docid of current document.
-** dlrDocData - doclist data for current document (including docid).
-** dlrDocDataBytes - length of same.
-** dlrAllDataBytes - length of all remaining data.
-** dlrPosData - position data for current document.
-** dlrPosDataLen - length of pos data for current document (incl POS_END).
-** dlrStep - step to current document.
-** dlrInit - initial for doclist of given type against given data.
-** dlrDestroy - clean up.
-**
-** Expected usage is something like:
-**
-**   DLReader reader;
-**   dlrInit(&reader, pData, nData);
-**   while( !dlrAtEnd(&reader) ){
-**     // calls to dlrDocid() and kin.
-**     dlrStep(&reader);
-**   }
-**   dlrDestroy(&reader);
-*/
-typedef struct DLReader {
-  DocListType iType;
-  const char *pData;
-  int nData;
-
-  sqlite_int64 iDocid;
-  int nElement;
-} DLReader;
-
-static int dlrAtEnd(DLReader *pReader){
-  assert( pReader->nData>=0 );
-  return pReader->nData<=0;
-}
-static sqlite_int64 dlrDocid(DLReader *pReader){
-  assert( !dlrAtEnd(pReader) );
-  return pReader->iDocid;
-}
-static const char *dlrDocData(DLReader *pReader){
-  assert( !dlrAtEnd(pReader) );
-  return pReader->pData;
-}
-static int dlrDocDataBytes(DLReader *pReader){
-  assert( !dlrAtEnd(pReader) );
-  return pReader->nElement;
-}
-static int dlrAllDataBytes(DLReader *pReader){
-  assert( !dlrAtEnd(pReader) );
-  return pReader->nData;
-}
-/* TODO(shess) Consider adding a field to track iDocid varint length
-** to make these two functions faster.  This might matter (a tiny bit)
-** for queries.
-*/
-static const char *dlrPosData(DLReader *pReader){
-  sqlite_int64 iDummy;
-  int n = fts3GetVarintSafe(pReader->pData, &iDummy, pReader->nElement);
-  if( !n ) return NULL;
-  assert( !dlrAtEnd(pReader) );
-  return pReader->pData+n;
-}
-static int dlrPosDataLen(DLReader *pReader){
-  sqlite_int64 iDummy;
-  int n = fts3GetVarint(pReader->pData, &iDummy);
-  assert( !dlrAtEnd(pReader) );
-  return pReader->nElement-n;
-}
-static int dlrStep(DLReader *pReader){
-  assert( !dlrAtEnd(pReader) );
-
-  /* Skip past current doclist element. */
-  assert( pReader->nElement<=pReader->nData );
-  pReader->pData += pReader->nElement;
-  pReader->nData -= pReader->nElement;
-
-  /* If there is more data, read the next doclist element. */
-  if( pReader->nData>0 ){
-    sqlite_int64 iDocidDelta;
-    int nTotal = 0;
-    int iDummy, n = fts3GetVarintSafe(pReader->pData, &iDocidDelta, pReader->nData);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    nTotal += n;
-    pReader->iDocid += iDocidDelta;
-    if( pReader->iType>=DL_POSITIONS ){
-      while( 1 ){
-        n = fts3GetVarint32Safe(pReader->pData+nTotal, &iDummy, pReader->nData-nTotal);
-        if( !n ) return SQLITE_CORRUPT_BKPT;
-        nTotal += n;
-        if( iDummy==POS_END ) break;
-        if( iDummy==POS_COLUMN ){
-          n = fts3GetVarint32Safe(pReader->pData+nTotal, &iDummy, pReader->nData-nTotal);
-          if( !n ) return SQLITE_CORRUPT_BKPT;
-          nTotal += n;
-        }else if( pReader->iType==DL_POSITIONS_OFFSETS ){
-          n = fts3GetVarint32Safe(pReader->pData+nTotal, &iDummy, pReader->nData-nTotal);
-          if( !n ) return SQLITE_CORRUPT_BKPT;
-          nTotal += n;
-          n = fts3GetVarint32Safe(pReader->pData+nTotal, &iDummy, pReader->nData-nTotal);
-          if( !n ) return SQLITE_CORRUPT_BKPT;
-          nTotal += n;
-        }
-      }
-    }
-    pReader->nElement = nTotal;
-    assert( pReader->nElement<=pReader->nData );
-  }
-  return SQLITE_OK;
-}
-static void dlrDestroy(DLReader *pReader){
-  SCRAMBLE(pReader);
-}
-static int dlrInit(DLReader *pReader, DocListType iType,
-                   const char *pData, int nData){
-  int rc;
-  assert( pData!=NULL && nData!=0 );
-  pReader->iType = iType;
-  pReader->pData = pData;
-  pReader->nData = nData;
-  pReader->nElement = 0;
-  pReader->iDocid = 0;
-
-  /* Load the first element's data.  There must be a first element. */
-  rc = dlrStep(pReader);
-  if( rc!=SQLITE_OK ) dlrDestroy(pReader);
-  return rc;
-}
-
-#ifndef NDEBUG
-/* Verify that the doclist can be validly decoded.  Also returns the
-** last docid found because it is convenient in other assertions for
-** DLWriter.
-*/
-static void docListValidate(DocListType iType, const char *pData, int nData,
-                            sqlite_int64 *pLastDocid){
-  sqlite_int64 iPrevDocid = 0;
-  assert( nData>0 );
-  assert( pData!=0 );
-  assert( pData+nData>pData );
-  while( nData!=0 ){
-    sqlite_int64 iDocidDelta;
-    int n = fts3GetVarint(pData, &iDocidDelta);
-    iPrevDocid += iDocidDelta;
-    if( iType>DL_DOCIDS ){
-      int iDummy;
-      while( 1 ){
-        n += fts3GetVarint32(pData+n, &iDummy);
-        if( iDummy==POS_END ) break;
-        if( iDummy==POS_COLUMN ){
-          n += fts3GetVarint32(pData+n, &iDummy);
-        }else if( iType>DL_POSITIONS ){
-          n += fts3GetVarint32(pData+n, &iDummy);
-          n += fts3GetVarint32(pData+n, &iDummy);
-        }
-        assert( n<=nData );
-      }
-    }
-    assert( n<=nData );
-    pData += n;
-    nData -= n;
-  }
-  if( pLastDocid ) *pLastDocid = iPrevDocid;
-}
-#define ASSERT_VALID_DOCLIST(i, p, n, o) docListValidate(i, p, n, o)
-#else
-#define ASSERT_VALID_DOCLIST(i, p, n, o) assert( 1 )
-#endif
-
-/*******************************************************************/
-/* DLWriter is used to write doclist data to a DataBuffer.  DLWriter
-** always appends to the buffer and does not own it.
-**
-** dlwInit - initialize to write a given type doclistto a buffer.
-** dlwDestroy - clear the writer's memory.  Does not free buffer.
-** dlwAppend - append raw doclist data to buffer.
-** dlwCopy - copy next doclist from reader to writer.
-** dlwAdd - construct doclist element and append to buffer.
-**    Only apply dlwAdd() to DL_DOCIDS doclists (else use PLWriter).
-*/
-typedef struct DLWriter {
-  DocListType iType;
-  DataBuffer *b;
-  sqlite_int64 iPrevDocid;
-#ifndef NDEBUG
-  int has_iPrevDocid;
-#endif
-} DLWriter;
-
-static void dlwInit(DLWriter *pWriter, DocListType iType, DataBuffer *b){
-  pWriter->b = b;
-  pWriter->iType = iType;
-  pWriter->iPrevDocid = 0;
-#ifndef NDEBUG
-  pWriter->has_iPrevDocid = 0;
-#endif
-}
-static void dlwDestroy(DLWriter *pWriter){
-  SCRAMBLE(pWriter);
-}
-/* iFirstDocid is the first docid in the doclist in pData.  It is
-** needed because pData may point within a larger doclist, in which
-** case the first item would be delta-encoded.
-**
-** iLastDocid is the final docid in the doclist in pData.  It is
-** needed to create the new iPrevDocid for future delta-encoding.  The
-** code could decode the passed doclist to recreate iLastDocid, but
-** the only current user (docListMerge) already has decoded this
-** information.
-*/
-/* TODO(shess) This has become just a helper for docListMerge.
-** Consider a refactor to make this cleaner.
-*/
-static int dlwAppend(DLWriter *pWriter,
-                     const char *pData, int nData,
-                     sqlite_int64 iFirstDocid, sqlite_int64 iLastDocid){
-  sqlite_int64 iDocid = 0;
-  char c[VARINT_MAX];
-  int nFirstOld, nFirstNew;     /* Old and new varint len of first docid. */
-#ifndef NDEBUG
-  sqlite_int64 iLastDocidDelta;
-#endif
-
-  /* Recode the initial docid as delta from iPrevDocid. */
-  nFirstOld = fts3GetVarintSafe(pData, &iDocid, nData);
-  if( !nFirstOld ) return SQLITE_CORRUPT_BKPT;
-  assert( nFirstOld<nData || (nFirstOld==nData && pWriter->iType==DL_DOCIDS) );
-  nFirstNew = fts3PutVarint(c, iFirstDocid-pWriter->iPrevDocid);
-
-  /* Verify that the incoming doclist is valid AND that it ends with
-  ** the expected docid.  This is essential because we'll trust this
-  ** docid in future delta-encoding.
-  */
-  ASSERT_VALID_DOCLIST(pWriter->iType, pData, nData, &iLastDocidDelta);
-  assert( iLastDocid==iFirstDocid-iDocid+iLastDocidDelta );
-
-  /* Append recoded initial docid and everything else.  Rest of docids
-  ** should have been delta-encoded from previous initial docid.
-  */
-  if( nFirstOld<nData ){
-    dataBufferAppend2(pWriter->b, c, nFirstNew,
-                      pData+nFirstOld, nData-nFirstOld);
-  }else{
-    dataBufferAppend(pWriter->b, c, nFirstNew);
-  }
-  pWriter->iPrevDocid = iLastDocid;
-  return SQLITE_OK;
-}
-static int dlwCopy(DLWriter *pWriter, DLReader *pReader){
-  return dlwAppend(pWriter, dlrDocData(pReader), dlrDocDataBytes(pReader),
-                   dlrDocid(pReader), dlrDocid(pReader));
-}
-static void dlwAdd(DLWriter *pWriter, sqlite_int64 iDocid){
-  char c[VARINT_MAX];
-  int n = fts3PutVarint(c, iDocid-pWriter->iPrevDocid);
-
-  /* Docids must ascend. */
-  assert( !pWriter->has_iPrevDocid || iDocid>pWriter->iPrevDocid );
-  assert( pWriter->iType==DL_DOCIDS );
-
-  dataBufferAppend(pWriter->b, c, n);
-  pWriter->iPrevDocid = iDocid;
-#ifndef NDEBUG
-  pWriter->has_iPrevDocid = 1;
-#endif
-}
-
-/*******************************************************************/
-/* PLReader is used to read data from a document's position list.  As
-** the caller steps through the list, data is cached so that varints
-** only need to be decoded once.
-**
-** plrInit, plrDestroy - create/destroy a reader.
-** plrColumn, plrPosition, plrStartOffset, plrEndOffset - accessors
-** plrAtEnd - at end of stream, only call plrDestroy once true.
-** plrStep - step to the next element.
-*/
-typedef struct PLReader {
-  /* These refer to the next position's data.  nData will reach 0 when
-  ** reading the last position, so plrStep() signals EOF by setting
-  ** pData to NULL.
-  */
-  const char *pData;
-  int nData;
-
-  DocListType iType;
-  int iColumn;         /* the last column read */
-  int iPosition;       /* the last position read */
-  int iStartOffset;    /* the last start offset read */
-  int iEndOffset;      /* the last end offset read */
-} PLReader;
-
-static int plrAtEnd(PLReader *pReader){
-  return pReader->pData==NULL;
-}
-static int plrColumn(PLReader *pReader){
-  assert( !plrAtEnd(pReader) );
-  return pReader->iColumn;
-}
-static int plrPosition(PLReader *pReader){
-  assert( !plrAtEnd(pReader) );
-  return pReader->iPosition;
-}
-static int plrStartOffset(PLReader *pReader){
-  assert( !plrAtEnd(pReader) );
-  return pReader->iStartOffset;
-}
-static int plrEndOffset(PLReader *pReader){
-  assert( !plrAtEnd(pReader) );
-  return pReader->iEndOffset;
-}
-static int plrStep(PLReader *pReader){
-  int i, n, nTotal = 0;
-
-  assert( !plrAtEnd(pReader) );
-
-  if( pReader->nData<=0 ){
-    pReader->pData = NULL;
-    return SQLITE_OK;
-  }
-
-  n = fts3GetVarint32Safe(pReader->pData, &i, pReader->nData);
-  if( !n ) return SQLITE_CORRUPT_BKPT;
-  nTotal += n;
-  if( i==POS_COLUMN ){
-    n = fts3GetVarint32Safe(pReader->pData+nTotal, &pReader->iColumn, pReader->nData-nTotal);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    nTotal += n;
-    pReader->iPosition = 0;
-    pReader->iStartOffset = 0;
-    n = fts3GetVarint32Safe(pReader->pData+nTotal, &i, pReader->nData-nTotal);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    nTotal += n;
-  }
-  /* Should never see adjacent column changes. */
-  assert( i!=POS_COLUMN );
-
-  if( i==POS_END ){
-    assert( nTotal<=pReader->nData );
-    pReader->nData = 0;
-    pReader->pData = NULL;
-    return SQLITE_OK;
-  }
-
-  pReader->iPosition += i-POS_BASE;
-  if( pReader->iType==DL_POSITIONS_OFFSETS ){
-    n = fts3GetVarint32Safe(pReader->pData+nTotal, &i, pReader->nData-nTotal);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    nTotal += n;
-    pReader->iStartOffset += i;
-    n = fts3GetVarint32Safe(pReader->pData+nTotal, &i, pReader->nData-nTotal);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    nTotal += n;
-    pReader->iEndOffset = pReader->iStartOffset+i;
-  }
-  assert( nTotal<=pReader->nData );
-  pReader->pData += nTotal;
-  pReader->nData -= nTotal;
-  return SQLITE_OK;
-}
-
-static void plrDestroy(PLReader *pReader){
-  SCRAMBLE(pReader);
-}
-static int plrInit(PLReader *pReader, DLReader *pDLReader){
-  int rc;
-  pReader->pData = dlrPosData(pDLReader);
-  pReader->nData = dlrPosDataLen(pDLReader);
-  pReader->iType = pDLReader->iType;
-  pReader->iColumn = 0;
-  pReader->iPosition = 0;
-  pReader->iStartOffset = 0;
-  pReader->iEndOffset = 0;
-  rc = plrStep(pReader);
-  if( rc!=SQLITE_OK ) plrDestroy(pReader);
-  return rc;
-}
-
-/*******************************************************************/
-/* PLWriter is used in constructing a document's position list.  As a
-** convenience, if iType is DL_DOCIDS, PLWriter becomes a no-op.
-** PLWriter writes to the associated DLWriter's buffer.
-**
-** plwInit - init for writing a document's poslist.
-** plwDestroy - clear a writer.
-** plwAdd - append position and offset information.
-** plwCopy - copy next position's data from reader to writer.
-** plwTerminate - add any necessary doclist terminator.
-**
-** Calling plwAdd() after plwTerminate() may result in a corrupt
-** doclist.
-*/
-/* TODO(shess) Until we've written the second item, we can cache the
-** first item's information.  Then we'd have three states:
-**
-** - initialized with docid, no positions.
-** - docid and one position.
-** - docid and multiple positions.
-**
-** Only the last state needs to actually write to dlw->b, which would
-** be an improvement in the DLCollector case.
-*/
-typedef struct PLWriter {
-  DLWriter *dlw;
-
-  int iColumn;    /* the last column written */
-  int iPos;       /* the last position written */
-  int iOffset;    /* the last start offset written */
-} PLWriter;
-
-/* TODO(shess) In the case where the parent is reading these values
-** from a PLReader, we could optimize to a copy if that PLReader has
-** the same type as pWriter.
-*/
-static void plwAdd(PLWriter *pWriter, int iColumn, int iPos,
-                   int iStartOffset, int iEndOffset){
-  /* Worst-case space for POS_COLUMN, iColumn, iPosDelta,
-  ** iStartOffsetDelta, and iEndOffsetDelta.
-  */
-  char c[5*VARINT_MAX];
-  int n = 0;
-
-  /* Ban plwAdd() after plwTerminate(). */
-  assert( pWriter->iPos!=-1 );
-
-  if( pWriter->dlw->iType==DL_DOCIDS ) return;
-
-  if( iColumn!=pWriter->iColumn ){
-    n += fts3PutVarint(c+n, POS_COLUMN);
-    n += fts3PutVarint(c+n, iColumn);
-    pWriter->iColumn = iColumn;
-    pWriter->iPos = 0;
-    pWriter->iOffset = 0;
-  }
-  assert( iPos>=pWriter->iPos );
-  n += fts3PutVarint(c+n, POS_BASE+(iPos-pWriter->iPos));
-  pWriter->iPos = iPos;
-  if( pWriter->dlw->iType==DL_POSITIONS_OFFSETS ){
-    assert( iStartOffset>=pWriter->iOffset );
-    n += fts3PutVarint(c+n, iStartOffset-pWriter->iOffset);
-    pWriter->iOffset = iStartOffset;
-    assert( iEndOffset>=iStartOffset );
-    n += fts3PutVarint(c+n, iEndOffset-iStartOffset);
-  }
-  dataBufferAppend(pWriter->dlw->b, c, n);
-}
-static void plwCopy(PLWriter *pWriter, PLReader *pReader){
-  plwAdd(pWriter, plrColumn(pReader), plrPosition(pReader),
-         plrStartOffset(pReader), plrEndOffset(pReader));
-}
-static void plwInit(PLWriter *pWriter, DLWriter *dlw, sqlite_int64 iDocid){
-  char c[VARINT_MAX];
-  int n;
-
-  pWriter->dlw = dlw;
-
-  /* Docids must ascend. */
-  assert( !pWriter->dlw->has_iPrevDocid || iDocid>pWriter->dlw->iPrevDocid );
-  n = fts3PutVarint(c, iDocid-pWriter->dlw->iPrevDocid);
-  dataBufferAppend(pWriter->dlw->b, c, n);
-  pWriter->dlw->iPrevDocid = iDocid;
-#ifndef NDEBUG
-  pWriter->dlw->has_iPrevDocid = 1;
-#endif
-
-  pWriter->iColumn = 0;
-  pWriter->iPos = 0;
-  pWriter->iOffset = 0;
-}
-/* TODO(shess) Should plwDestroy() also terminate the doclist?  But
-** then plwDestroy() would no longer be just a destructor, it would
-** also be doing work, which isn't consistent with the overall idiom.
-** Another option would be for plwAdd() to always append any necessary
-** terminator, so that the output is always correct.  But that would
-** add incremental work to the common case with the only benefit being
-** API elegance.  Punt for now.
-*/
-static void plwTerminate(PLWriter *pWriter){
-  if( pWriter->dlw->iType>DL_DOCIDS ){
-    char c[VARINT_MAX];
-    int n = fts3PutVarint(c, POS_END);
-    dataBufferAppend(pWriter->dlw->b, c, n);
-  }
-#ifndef NDEBUG
-  /* Mark as terminated for assert in plwAdd(). */
-  pWriter->iPos = -1;
-#endif
-}
-static void plwDestroy(PLWriter *pWriter){
-  SCRAMBLE(pWriter);
-}
-
-/*******************************************************************/
-/* DLCollector wraps PLWriter and DLWriter to provide a
-** dynamically-allocated doclist area to use during tokenization.
-**
-** dlcNew - malloc up and initialize a collector.
-** dlcDelete - destroy a collector and all contained items.
-** dlcAddPos - append position and offset information.
-** dlcAddDoclist - add the collected doclist to the given buffer.
-** dlcNext - terminate the current document and open another.
-*/
-typedef struct DLCollector {
-  DataBuffer b;
-  DLWriter dlw;
-  PLWriter plw;
-} DLCollector;
-
-/* TODO(shess) This could also be done by calling plwTerminate() and
-** dataBufferAppend().  I tried that, expecting nominal performance
-** differences, but it seemed to pretty reliably be worth 1% to code
-** it this way.  I suspect it is the incremental malloc overhead (some
-** percentage of the plwTerminate() calls will cause a realloc), so
-** this might be worth revisiting if the DataBuffer implementation
-** changes.
-*/
-static void dlcAddDoclist(DLCollector *pCollector, DataBuffer *b){
-  if( pCollector->dlw.iType>DL_DOCIDS ){
-    char c[VARINT_MAX];
-    int n = fts3PutVarint(c, POS_END);
-    dataBufferAppend2(b, pCollector->b.pData, pCollector->b.nData, c, n);
-  }else{
-    dataBufferAppend(b, pCollector->b.pData, pCollector->b.nData);
-  }
-}
-static void dlcNext(DLCollector *pCollector, sqlite_int64 iDocid){
-  plwTerminate(&pCollector->plw);
-  plwDestroy(&pCollector->plw);
-  plwInit(&pCollector->plw, &pCollector->dlw, iDocid);
-}
-static void dlcAddPos(DLCollector *pCollector, int iColumn, int iPos,
-                      int iStartOffset, int iEndOffset){
-  plwAdd(&pCollector->plw, iColumn, iPos, iStartOffset, iEndOffset);
-}
-
-static DLCollector *dlcNew(sqlite_int64 iDocid, DocListType iType){
-  DLCollector *pCollector = sqlite3_malloc(sizeof(DLCollector));
-  dataBufferInit(&pCollector->b, 0);
-  dlwInit(&pCollector->dlw, iType, &pCollector->b);
-  plwInit(&pCollector->plw, &pCollector->dlw, iDocid);
-  return pCollector;
-}
-static void dlcDelete(DLCollector *pCollector){
-  plwDestroy(&pCollector->plw);
-  dlwDestroy(&pCollector->dlw);
-  dataBufferDestroy(&pCollector->b);
-  SCRAMBLE(pCollector);
-  sqlite3_free(pCollector);
-}
-
-
-/* Copy the doclist data of iType in pData/nData into *out, trimming
-** unnecessary data as we go.  Only columns matching iColumn are
-** copied, all columns copied if iColumn is -1.  Elements with no
-** matching columns are dropped.  The output is an iOutType doclist.
-*/
-/* NOTE(shess) This code is only valid after all doclists are merged.
-** If this is run before merges, then doclist items which represent
-** deletion will be trimmed, and will thus not effect a deletion
-** during the merge.
-*/
-static int docListTrim(DocListType iType, const char *pData, int nData,
-                       int iColumn, DocListType iOutType, DataBuffer *out){
-  DLReader dlReader;
-  DLWriter dlWriter;
-  int rc;
-
-  assert( iOutType<=iType );
-
-  rc = dlrInit(&dlReader, iType, pData, nData);
-  if( rc!=SQLITE_OK ) return rc;
-  dlwInit(&dlWriter, iOutType, out);
-
-  while( !dlrAtEnd(&dlReader) ){
-    PLReader plReader;
-    PLWriter plWriter;
-    int match = 0;
-
-    rc = plrInit(&plReader, &dlReader);
-    if( rc!=SQLITE_OK ) break;
-
-    while( !plrAtEnd(&plReader) ){
-      if( iColumn==-1 || plrColumn(&plReader)==iColumn ){
-        if( !match ){
-          plwInit(&plWriter, &dlWriter, dlrDocid(&dlReader));
-          match = 1;
-        }
-        plwAdd(&plWriter, plrColumn(&plReader), plrPosition(&plReader),
-               plrStartOffset(&plReader), plrEndOffset(&plReader));
-      }
-      rc = plrStep(&plReader);
-      if( rc!=SQLITE_OK ){
-        plrDestroy(&plReader);
-        goto err;
-      }
-    }
-    if( match ){
-      plwTerminate(&plWriter);
-      plwDestroy(&plWriter);
-    }
-
-    plrDestroy(&plReader);
-    rc = dlrStep(&dlReader);
-    if( rc!=SQLITE_OK ) break;
-  }
-err:
-  dlwDestroy(&dlWriter);
-  dlrDestroy(&dlReader);
-  return rc;
-}
-
-/* Used by docListMerge() to keep doclists in the ascending order by
-** docid, then ascending order by age (so the newest comes first).
-*/
-typedef struct OrderedDLReader {
-  DLReader *pReader;
-
-  /* TODO(shess) If we assume that docListMerge pReaders is ordered by
-  ** age (which we do), then we could use pReader comparisons to break
-  ** ties.
-  */
-  int idx;
-} OrderedDLReader;
-
-/* Order eof to end, then by docid asc, idx desc. */
-static int orderedDLReaderCmp(OrderedDLReader *r1, OrderedDLReader *r2){
-  if( dlrAtEnd(r1->pReader) ){
-    if( dlrAtEnd(r2->pReader) ) return 0;  /* Both atEnd(). */
-    return 1;                              /* Only r1 atEnd(). */
-  }
-  if( dlrAtEnd(r2->pReader) ) return -1;   /* Only r2 atEnd(). */
-
-  if( dlrDocid(r1->pReader)<dlrDocid(r2->pReader) ) return -1;
-  if( dlrDocid(r1->pReader)>dlrDocid(r2->pReader) ) return 1;
-
-  /* Descending on idx. */
-  return r2->idx-r1->idx;
-}
-
-/* Bubble p[0] to appropriate place in p[1..n-1].  Assumes that
-** p[1..n-1] is already sorted.
-*/
-/* TODO(shess) Is this frequent enough to warrant a binary search?
-** Before implementing that, instrument the code to check.  In most
-** current usage, I expect that p[0] will be less than p[1] a very
-** high proportion of the time.
-*/
-static void orderedDLReaderReorder(OrderedDLReader *p, int n){
-  while( n>1 && orderedDLReaderCmp(p, p+1)>0 ){
-    OrderedDLReader tmp = p[0];
-    p[0] = p[1];
-    p[1] = tmp;
-    n--;
-    p++;
-  }
-}
-
-/* Given an array of doclist readers, merge their doclist elements
-** into out in sorted order (by docid), dropping elements from older
-** readers when there is a duplicate docid.  pReaders is assumed to be
-** ordered by age, oldest first.
-*/
-/* TODO(shess) nReaders must be <= MERGE_COUNT.  This should probably
-** be fixed.
-*/
-static int docListMerge(DataBuffer *out,
-                        DLReader *pReaders, int nReaders){
-  OrderedDLReader readers[MERGE_COUNT];
-  DLWriter writer;
-  int i, n;
-  const char *pStart = 0;
-  int nStart = 0;
-  sqlite_int64 iFirstDocid = 0, iLastDocid = 0;
-  int rc = SQLITE_OK;
-
-  assert( nReaders>0 );
-  if( nReaders==1 ){
-    dataBufferAppend(out, dlrDocData(pReaders), dlrAllDataBytes(pReaders));
-    return SQLITE_OK;
-  }
-
-  assert( nReaders<=MERGE_COUNT );
-  n = 0;
-  for(i=0; i<nReaders; i++){
-    assert( pReaders[i].iType==pReaders[0].iType );
-    readers[i].pReader = pReaders+i;
-    readers[i].idx = i;
-    n += dlrAllDataBytes(&pReaders[i]);
-  }
-  /* Conservatively size output to sum of inputs.  Output should end
-  ** up strictly smaller than input.
-  */
-  dataBufferExpand(out, n);
-
-  /* Get the readers into sorted order. */
-  while( i-->0 ){
-    orderedDLReaderReorder(readers+i, nReaders-i);
-  }
-
-  dlwInit(&writer, pReaders[0].iType, out);
-  while( !dlrAtEnd(readers[0].pReader) ){
-    sqlite_int64 iDocid = dlrDocid(readers[0].pReader);
-
-    /* If this is a continuation of the current buffer to copy, extend
-    ** that buffer.  memcpy() seems to be more efficient if it has a
-    ** lots of data to copy.
-    */
-    if( dlrDocData(readers[0].pReader)==pStart+nStart ){
-      nStart += dlrDocDataBytes(readers[0].pReader);
-    }else{
-      if( pStart!=0 ){
-        rc = dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
-        if( rc!=SQLITE_OK ) goto err;
-      }
-      pStart = dlrDocData(readers[0].pReader);
-      nStart = dlrDocDataBytes(readers[0].pReader);
-      iFirstDocid = iDocid;
-    }
-    iLastDocid = iDocid;
-    rc = dlrStep(readers[0].pReader);
-    if( rc!= SQLITE_OK ) goto err;
-
-    /* Drop all of the older elements with the same docid. */
-    for(i=1; i<nReaders &&
-             !dlrAtEnd(readers[i].pReader) &&
-             dlrDocid(readers[i].pReader)==iDocid; i++){
-      rc = dlrStep(readers[i].pReader);
-      if( rc!=SQLITE_OK ) goto err;
-    }
-
-    /* Get the readers back into order. */
-    while( i-->0 ){
-      orderedDLReaderReorder(readers+i, nReaders-i);
-    }
-  }
-
-  /* Copy over any remaining elements. */
-  if( nStart>0 ) rc = dlwAppend(&writer, pStart, nStart, iFirstDocid, iLastDocid);
-err:
-  dlwDestroy(&writer);
-  return rc;
-}
-
-/* Helper function for posListUnion().  Compares the current position
-** between left and right, returning as standard C idiom of <0 if
-** left<right, >0 if left>right, and 0 if left==right.  "End" always
-** compares greater.
-*/
-static int posListCmp(PLReader *pLeft, PLReader *pRight){
-  assert( pLeft->iType==pRight->iType );
-  if( pLeft->iType==DL_DOCIDS ) return 0;
-
-  if( plrAtEnd(pLeft) ) return plrAtEnd(pRight) ? 0 : 1;
-  if( plrAtEnd(pRight) ) return -1;
-
-  if( plrColumn(pLeft)<plrColumn(pRight) ) return -1;
-  if( plrColumn(pLeft)>plrColumn(pRight) ) return 1;
-
-  if( plrPosition(pLeft)<plrPosition(pRight) ) return -1;
-  if( plrPosition(pLeft)>plrPosition(pRight) ) return 1;
-  if( pLeft->iType==DL_POSITIONS ) return 0;
-
-  if( plrStartOffset(pLeft)<plrStartOffset(pRight) ) return -1;
-  if( plrStartOffset(pLeft)>plrStartOffset(pRight) ) return 1;
-
-  if( plrEndOffset(pLeft)<plrEndOffset(pRight) ) return -1;
-  if( plrEndOffset(pLeft)>plrEndOffset(pRight) ) return 1;
-
-  return 0;
-}
-
-/* Write the union of position lists in pLeft and pRight to pOut.
-** "Union" in this case meaning "All unique position tuples".  Should
-** work with any doclist type, though both inputs and the output
-** should be the same type.
-*/
-static int posListUnion(DLReader *pLeft, DLReader *pRight, DLWriter *pOut){
-  PLReader left, right;
-  PLWriter writer;
-  int rc;
-
-  assert( dlrDocid(pLeft)==dlrDocid(pRight) );
-  assert( pLeft->iType==pRight->iType );
-  assert( pLeft->iType==pOut->iType );
-
-  rc = plrInit(&left, pLeft);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = plrInit(&right, pRight);
-  if( rc!=SQLITE_OK ){
-    plrDestroy(&left);
-    return rc;
-  }
-  plwInit(&writer, pOut, dlrDocid(pLeft));
-
-  while( !plrAtEnd(&left) || !plrAtEnd(&right) ){
-    int c = posListCmp(&left, &right);
-    if( c<0 ){
-      plwCopy(&writer, &left);
-      rc = plrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-    }else if( c>0 ){
-      plwCopy(&writer, &right);
-      rc = plrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else{
-      plwCopy(&writer, &left);
-      rc = plrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-      rc = plrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }
-  }
-
-  plwTerminate(&writer);
-  plwDestroy(&writer);
-  plrDestroy(&left);
-  plrDestroy(&right);
-  return rc;
-}
-
-/* Write the union of doclists in pLeft and pRight to pOut.  For
-** docids in common between the inputs, the union of the position
-** lists is written.  Inputs and outputs are always type DL_DEFAULT.
-*/
-static int docListUnion(
-  const char *pLeft, int nLeft,
-  const char *pRight, int nRight,
-  DataBuffer *pOut      /* Write the combined doclist here */
-){
-  DLReader left, right;
-  DLWriter writer;
-  int rc;
-
-  if( nLeft==0 ){
-    if( nRight!=0) dataBufferAppend(pOut, pRight, nRight);
-    return SQLITE_OK;
-  }
-  if( nRight==0 ){
-    dataBufferAppend(pOut, pLeft, nLeft);
-    return SQLITE_OK;
-  }
-
-  rc = dlrInit(&left, DL_DEFAULT, pLeft, nLeft);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = dlrInit(&right, DL_DEFAULT, pRight, nRight);
-  if( rc!=SQLITE_OK){
-    dlrDestroy(&left);
-    return rc;
-  }
-  dlwInit(&writer, DL_DEFAULT, pOut);
-
-  while( !dlrAtEnd(&left) || !dlrAtEnd(&right) ){
-    if( dlrAtEnd(&right) ){
-      rc = dlwCopy(&writer, &left);
-      if( rc!=SQLITE_OK) break;
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK) break;
-    }else if( dlrAtEnd(&left) ){
-      rc = dlwCopy(&writer, &right);
-      if( rc!=SQLITE_OK ) break;
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else if( dlrDocid(&left)<dlrDocid(&right) ){
-      rc = dlwCopy(&writer, &left);
-      if( rc!=SQLITE_OK ) break;
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-    }else if( dlrDocid(&left)>dlrDocid(&right) ){
-      rc = dlwCopy(&writer, &right);
-      if( rc!=SQLITE_OK ) break;
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else{
-      rc = posListUnion(&left, &right, &writer);
-      if( rc!=SQLITE_OK ) break;
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }
-  }
-
-  dlrDestroy(&left);
-  dlrDestroy(&right);
-  dlwDestroy(&writer);
-  return rc;
-}
-
-/* 
-** This function is used as part of the implementation of phrase and
-** NEAR matching.
-**
-** pLeft and pRight are DLReaders positioned to the same docid in
-** lists of type DL_POSITION. This function writes an entry to the
-** DLWriter pOut for each position in pRight that is less than
-** (nNear+1) greater (but not equal to or smaller) than a position 
-** in pLeft. For example, if nNear is 0, and the positions contained
-** by pLeft and pRight are:
-**
-**    pLeft:  5 10 15 20
-**    pRight: 6  9 17 21
-**
-** then the docid is added to pOut. If pOut is of type DL_POSITIONS,
-** then a positionids "6" and "21" are also added to pOut.
-**
-** If boolean argument isSaveLeft is true, then positionids are copied
-** from pLeft instead of pRight. In the example above, the positions "5"
-** and "20" would be added instead of "6" and "21".
-*/
-static int posListPhraseMerge(
-  DLReader *pLeft, 
-  DLReader *pRight,
-  int nNear,
-  int isSaveLeft,
-  DLWriter *pOut
-){
-  PLReader left, right;
-  PLWriter writer;
-  int match = 0;
-  int rc;
-
-  assert( dlrDocid(pLeft)==dlrDocid(pRight) );
-  assert( pOut->iType!=DL_POSITIONS_OFFSETS );
-
-  rc = plrInit(&left, pLeft);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = plrInit(&right, pRight);
-  if( rc!=SQLITE_OK ){
-    plrDestroy(&left);
-    return rc;
-  }
-
-  while( !plrAtEnd(&left) && !plrAtEnd(&right) ){
-    if( plrColumn(&left)<plrColumn(&right) ){
-      rc = plrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-    }else if( plrColumn(&left)>plrColumn(&right) ){
-      rc = plrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else if( plrPosition(&left)>=plrPosition(&right) ){
-      rc = plrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else{
-      if( (plrPosition(&right)-plrPosition(&left))<=(nNear+1) ){
-        if( !match ){
-          plwInit(&writer, pOut, dlrDocid(pLeft));
-          match = 1;
-        }
-        if( !isSaveLeft ){
-          plwAdd(&writer, plrColumn(&right), plrPosition(&right), 0, 0);
-        }else{
-          plwAdd(&writer, plrColumn(&left), plrPosition(&left), 0, 0);
-        }
-        rc = plrStep(&right);
-        if( rc!=SQLITE_OK ) break;
-      }else{
-        rc = plrStep(&left);
-        if( rc!=SQLITE_OK ) break;
-      }
-    }
-  }
-
-  if( match ){
-    plwTerminate(&writer);
-    plwDestroy(&writer);
-  }
-
-  plrDestroy(&left);
-  plrDestroy(&right);
-  return rc;
-}
-
-/*
-** Compare the values pointed to by the PLReaders passed as arguments. 
-** Return -1 if the value pointed to by pLeft is considered less than
-** the value pointed to by pRight, +1 if it is considered greater
-** than it, or 0 if it is equal. i.e.
-**
-**     (*pLeft - *pRight)
-**
-** A PLReader that is in the EOF condition is considered greater than
-** any other. If neither argument is in EOF state, the return value of
-** plrColumn() is used. If the plrColumn() values are equal, the
-** comparison is on the basis of plrPosition().
-*/
-static int plrCompare(PLReader *pLeft, PLReader *pRight){
-  assert(!plrAtEnd(pLeft) || !plrAtEnd(pRight));
-
-  if( plrAtEnd(pRight) || plrAtEnd(pLeft) ){
-    return (plrAtEnd(pRight) ? -1 : 1);
-  }
-  if( plrColumn(pLeft)!=plrColumn(pRight) ){
-    return ((plrColumn(pLeft)<plrColumn(pRight)) ? -1 : 1);
-  }
-  if( plrPosition(pLeft)!=plrPosition(pRight) ){
-    return ((plrPosition(pLeft)<plrPosition(pRight)) ? -1 : 1);
-  }
-  return 0;
-}
-
-/* We have two doclists with positions:  pLeft and pRight. Depending
-** on the value of the nNear parameter, perform either a phrase
-** intersection (if nNear==0) or a NEAR intersection (if nNear>0)
-** and write the results into pOut.
-**
-** A phrase intersection means that two documents only match
-** if pLeft.iPos+1==pRight.iPos.
-**
-** A NEAR intersection means that two documents only match if 
-** (abs(pLeft.iPos-pRight.iPos)<nNear).
-**
-** If a NEAR intersection is requested, then the nPhrase argument should
-** be passed the number of tokens in the two operands to the NEAR operator
-** combined. For example:
-**
-**       Query syntax               nPhrase
-**      ------------------------------------
-**       "A B C" NEAR "D E"         5
-**       A NEAR B                   2
-**
-** iType controls the type of data written to pOut.  If iType is
-** DL_POSITIONS, the positions are those from pRight.
-*/
-static int docListPhraseMerge(
-  const char *pLeft, int nLeft,
-  const char *pRight, int nRight,
-  int nNear,            /* 0 for a phrase merge, non-zero for a NEAR merge */
-  int nPhrase,          /* Number of tokens in left+right operands to NEAR */
-  DocListType iType,    /* Type of doclist to write to pOut */
-  DataBuffer *pOut      /* Write the combined doclist here */
-){
-  DLReader left, right;
-  DLWriter writer;
-  int rc;
-
-  /* These two buffers are used in the 'while', but are declared here
-  ** to simplify error-handling.
-  */
-  DataBuffer one = {0, 0, 0};
-  DataBuffer two = {0, 0, 0};
-
-  if( nLeft==0 || nRight==0 ) return SQLITE_OK;
-
-  assert( iType!=DL_POSITIONS_OFFSETS );
-
-  rc = dlrInit(&left, DL_POSITIONS, pLeft, nLeft);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = dlrInit(&right, DL_POSITIONS, pRight, nRight);
-  if( rc!=SQLITE_OK ){
-    dlrDestroy(&left);
-    return rc;
-  }
-  dlwInit(&writer, iType, pOut);
-
-  while( !dlrAtEnd(&left) && !dlrAtEnd(&right) ){
-    if( dlrDocid(&left)<dlrDocid(&right) ){
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) goto err;
-    }else if( dlrDocid(&right)<dlrDocid(&left) ){
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) goto err;
-    }else{
-      if( nNear==0 ){
-        rc = posListPhraseMerge(&left, &right, 0, 0, &writer);
-        if( rc!=SQLITE_OK ) goto err;
-      }else{
-        /* This case occurs when two terms (simple terms or phrases) are
-         * connected by a NEAR operator, span (nNear+1). i.e.
-         *
-         *     '"terrible company" NEAR widget'
-         */
-        DLWriter dlwriter2;
-        DLReader dr1 = {0, 0, 0, 0, 0};
-        DLReader dr2 = {0, 0, 0, 0, 0};
-
-        dlwInit(&dlwriter2, iType, &one);
-        rc = posListPhraseMerge(&right, &left, nNear-3+nPhrase, 1, &dlwriter2);
-        if( rc!=SQLITE_OK ) goto err;
-        dlwInit(&dlwriter2, iType, &two);
-        rc = posListPhraseMerge(&left, &right, nNear-1, 0, &dlwriter2);
-        if( rc!=SQLITE_OK ) goto err;
-
-        if( one.nData){
-          rc = dlrInit(&dr1, iType, one.pData, one.nData);
-          if( rc!=SQLITE_OK ) goto err;
-        }
-        if( two.nData){
-          rc = dlrInit(&dr2, iType, two.pData, two.nData);
-          if( rc!=SQLITE_OK ) goto err;
-        }
-
-        if( !dlrAtEnd(&dr1) || !dlrAtEnd(&dr2) ){
-          PLReader pr1 = {0};
-          PLReader pr2 = {0};
-
-          PLWriter plwriter;
-          plwInit(&plwriter, &writer, dlrDocid(dlrAtEnd(&dr1)?&dr2:&dr1));
-
-          if( one.nData ){
-            rc = plrInit(&pr1, &dr1);
-            if( rc!=SQLITE_OK ) goto err;
-          }
-          if( two.nData ){
-            rc = plrInit(&pr2, &dr2);
-            if( rc!=SQLITE_OK ) goto err;
-          }
-          while( !plrAtEnd(&pr1) || !plrAtEnd(&pr2) ){
-            int iCompare = plrCompare(&pr1, &pr2);
-            switch( iCompare ){
-              case -1:
-                plwCopy(&plwriter, &pr1);
-                rc = plrStep(&pr1);
-                if( rc!=SQLITE_OK ) goto err;
-                break;
-              case 1:
-                plwCopy(&plwriter, &pr2);
-                rc = plrStep(&pr2);
-                if( rc!=SQLITE_OK ) goto err;
-                break;
-              case 0:
-                plwCopy(&plwriter, &pr1);
-                rc = plrStep(&pr1);
-                if( rc!=SQLITE_OK ) goto err;
-                rc = plrStep(&pr2);
-                if( rc!=SQLITE_OK ) goto err;
-                break;
-            }
-          }
-          plwTerminate(&plwriter);
-        }
-        dataBufferReset(&one);
-        dataBufferReset(&two);
-      }
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) goto err;
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) goto err;
-    }
-  }
-
-err:
-  dataBufferDestroy(&one);
-  dataBufferDestroy(&two);
-  dlrDestroy(&left);
-  dlrDestroy(&right);
-  dlwDestroy(&writer);
-  return rc;
-}
-
-/* We have two DL_DOCIDS doclists:  pLeft and pRight.
-** Write the intersection of these two doclists into pOut as a
-** DL_DOCIDS doclist.
-*/
-static int docListAndMerge(
-  const char *pLeft, int nLeft,
-  const char *pRight, int nRight,
-  DataBuffer *pOut      /* Write the combined doclist here */
-){
-  DLReader left, right;
-  DLWriter writer;
-  int rc;
-
-  if( nLeft==0 || nRight==0 ) return SQLITE_OK;
-
-  rc = dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = dlrInit(&right, DL_DOCIDS, pRight, nRight);
-  if( rc!=SQLITE_OK ){
-    dlrDestroy(&left);
-    return rc;
-  }
-  dlwInit(&writer, DL_DOCIDS, pOut);
-
-  while( !dlrAtEnd(&left) && !dlrAtEnd(&right) ){
-    if( dlrDocid(&left)<dlrDocid(&right) ){
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-    }else if( dlrDocid(&right)<dlrDocid(&left) ){
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else{
-      dlwAdd(&writer, dlrDocid(&left));
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }
-  }
-
-  dlrDestroy(&left);
-  dlrDestroy(&right);
-  dlwDestroy(&writer);
-  return rc;
-}
-
-/* We have two DL_DOCIDS doclists:  pLeft and pRight.
-** Write the union of these two doclists into pOut as a
-** DL_DOCIDS doclist.
-*/
-static int docListOrMerge(
-  const char *pLeft, int nLeft,
-  const char *pRight, int nRight,
-  DataBuffer *pOut      /* Write the combined doclist here */
-){
-  DLReader left, right;
-  DLWriter writer;
-  int rc;
-
-  if( nLeft==0 ){
-    if( nRight!=0 ) dataBufferAppend(pOut, pRight, nRight);
-    return SQLITE_OK;
-  }
-  if( nRight==0 ){
-    dataBufferAppend(pOut, pLeft, nLeft);
-    return SQLITE_OK;
-  }
-
-  rc = dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = dlrInit(&right, DL_DOCIDS, pRight, nRight);
-  if( rc!=SQLITE_OK ){
-    dlrDestroy(&left);
-    return rc;
-  }
-  dlwInit(&writer, DL_DOCIDS, pOut);
-
-  while( !dlrAtEnd(&left) || !dlrAtEnd(&right) ){
-    if( dlrAtEnd(&right) ){
-      dlwAdd(&writer, dlrDocid(&left));
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-    }else if( dlrAtEnd(&left) ){
-      dlwAdd(&writer, dlrDocid(&right));
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else if( dlrDocid(&left)<dlrDocid(&right) ){
-      dlwAdd(&writer, dlrDocid(&left));
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-    }else if( dlrDocid(&right)<dlrDocid(&left) ){
-      dlwAdd(&writer, dlrDocid(&right));
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }else{
-      dlwAdd(&writer, dlrDocid(&left));
-      rc = dlrStep(&left);
-      if( rc!=SQLITE_OK ) break;
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) break;
-    }
-  }
-
-  dlrDestroy(&left);
-  dlrDestroy(&right);
-  dlwDestroy(&writer);
-  return rc;
-}
-
-/* We have two DL_DOCIDS doclists:  pLeft and pRight.
-** Write into pOut as DL_DOCIDS doclist containing all documents that
-** occur in pLeft but not in pRight.
-*/
-static int docListExceptMerge(
-  const char *pLeft, int nLeft,
-  const char *pRight, int nRight,
-  DataBuffer *pOut      /* Write the combined doclist here */
-){
-  DLReader left, right;
-  DLWriter writer;
-  int rc;
-
-  if( nLeft==0 ) return SQLITE_OK;
-  if( nRight==0 ){
-    dataBufferAppend(pOut, pLeft, nLeft);
-    return SQLITE_OK;
-  }
-
-  rc = dlrInit(&left, DL_DOCIDS, pLeft, nLeft);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = dlrInit(&right, DL_DOCIDS, pRight, nRight);
-  if( rc!=SQLITE_OK ){
-    dlrDestroy(&left);
-    return rc;
-  }
-  dlwInit(&writer, DL_DOCIDS, pOut);
-
-  while( !dlrAtEnd(&left) ){
-    while( !dlrAtEnd(&right) && dlrDocid(&right)<dlrDocid(&left) ){
-      rc = dlrStep(&right);
-      if( rc!=SQLITE_OK ) goto err;
-    }
-    if( dlrAtEnd(&right) || dlrDocid(&left)<dlrDocid(&right) ){
-      dlwAdd(&writer, dlrDocid(&left));
-    }
-    rc = dlrStep(&left);
-    if( rc!=SQLITE_OK ) break;
-  }
-
-err:
-  dlrDestroy(&left);
-  dlrDestroy(&right);
-  dlwDestroy(&writer);
-  return rc;
-}
-
-static char *string_dup_n(const char *s, int n){
-  char *str = sqlite3_malloc(n + 1);
-  memcpy(str, s, n);
-  str[n] = '\0';
-  return str;
-}
-
-/* Duplicate a string; the caller must free() the returned string.
- * (We don't use strdup() since it is not part of the standard C library and
- * may not be available everywhere.) */
-static char *string_dup(const char *s){
-  return string_dup_n(s, strlen(s));
-}
-
-/* Format a string, replacing each occurrence of the % character with
- * zDb.zName.  This may be more convenient than sqlite_mprintf()
- * when one string is used repeatedly in a format string.
- * The caller must free() the returned string. */
-static char *string_format(const char *zFormat,
-                           const char *zDb, const char *zName){
-  const char *p;
-  size_t len = 0;
-  size_t nDb = strlen(zDb);
-  size_t nName = strlen(zName);
-  size_t nFullTableName = nDb+1+nName;
-  char *result;
-  char *r;
-
-  /* first compute length needed */
-  for(p = zFormat ; *p ; ++p){
-    len += (*p=='%' ? nFullTableName : 1);
-  }
-  len += 1;  /* for null terminator */
-
-  r = result = sqlite3_malloc(len);
-  for(p = zFormat; *p; ++p){
-    if( *p=='%' ){
-      memcpy(r, zDb, nDb);
-      r += nDb;
-      *r++ = '.';
-      memcpy(r, zName, nName);
-      r += nName;
-    } else {
-      *r++ = *p;
-    }
-  }
-  *r++ = '\0';
-  assert( r == result + len );
-  return result;
-}
-
-static int sql_exec(sqlite3 *db, const char *zDb, const char *zName,
-                    const char *zFormat){
-  char *zCommand = string_format(zFormat, zDb, zName);
-  int rc;
-  FTSTRACE(("FTS3 sql: %s\n", zCommand));
-  rc = sqlite3_exec(db, zCommand, NULL, 0, NULL);
-  sqlite3_free(zCommand);
-  return rc;
-}
-
-static int sql_prepare(sqlite3 *db, const char *zDb, const char *zName,
-                       sqlite3_stmt **ppStmt, const char *zFormat){
-  char *zCommand = string_format(zFormat, zDb, zName);
-  int rc;
-  FTSTRACE(("FTS3 prepare: %s\n", zCommand));
-  rc = sqlite3_prepare_v2(db, zCommand, -1, ppStmt, NULL);
-  sqlite3_free(zCommand);
-  return rc;
-}
-
-/* end utility functions */
-
-/* Forward reference */
-typedef struct fulltext_vtab fulltext_vtab;
-
-/*
-** An instance of the following structure keeps track of generated
-** matching-word offset information and snippets.
-*/
-typedef struct Snippet {
-  int nMatch;     /* Total number of matches */
-  int nAlloc;     /* Space allocated for aMatch[] */
-  struct snippetMatch { /* One entry for each matching term */
-    char snStatus;       /* Status flag for use while constructing snippets */
-    short int iCol;      /* The column that contains the match */
-    short int iTerm;     /* The index in Query.pTerms[] of the matching term */
-    int iToken;          /* The index of the matching document token */
-    short int nByte;     /* Number of bytes in the term */
-    int iStart;          /* The offset to the first character of the term */
-  } *aMatch;      /* Points to space obtained from malloc */
-  char *zOffset;  /* Text rendering of aMatch[] */
-  int nOffset;    /* strlen(zOffset) */
-  char *zSnippet; /* Snippet text */
-  int nSnippet;   /* strlen(zSnippet) */
-} Snippet;
-
-
-typedef enum QueryType {
-  QUERY_GENERIC,   /* table scan */
-  QUERY_DOCID,     /* lookup by docid */
-  QUERY_FULLTEXT   /* QUERY_FULLTEXT + [i] is a full-text search for column i*/
-} QueryType;
-
-typedef enum fulltext_statement {
-  CONTENT_INSERT_STMT,
-  CONTENT_SELECT_STMT,
-  CONTENT_UPDATE_STMT,
-  CONTENT_DELETE_STMT,
-  CONTENT_EXISTS_STMT,
-
-  BLOCK_INSERT_STMT,
-  BLOCK_SELECT_STMT,
-  BLOCK_DELETE_STMT,
-  BLOCK_DELETE_ALL_STMT,
-
-  SEGDIR_MAX_INDEX_STMT,
-  SEGDIR_SET_STMT,
-  SEGDIR_SELECT_LEVEL_STMT,
-  SEGDIR_SPAN_STMT,
-  SEGDIR_DELETE_STMT,
-  SEGDIR_SELECT_SEGMENT_STMT,
-  SEGDIR_SELECT_ALL_STMT,
-  SEGDIR_DELETE_ALL_STMT,
-  SEGDIR_COUNT_STMT,
-
-  MAX_STMT                     /* Always at end! */
-} fulltext_statement;
-
-/* These must exactly match the enum above. */
-/* TODO(shess): Is there some risk that a statement will be used in two
-** cursors at once, e.g.  if a query joins a virtual table to itself?
-** If so perhaps we should move some of these to the cursor object.
-*/
-static const char *const fulltext_zStatement[MAX_STMT] = {
-  /* CONTENT_INSERT */ NULL,  /* generated in contentInsertStatement() */
-  /* CONTENT_SELECT */ NULL,  /* generated in contentSelectStatement() */
-  /* CONTENT_UPDATE */ NULL,  /* generated in contentUpdateStatement() */
-  /* CONTENT_DELETE */ "delete from %_content where docid = ?",
-  /* CONTENT_EXISTS */ "select docid from %_content limit 1",
-
-  /* BLOCK_INSERT */
-  "insert into %_segments (blockid, block) values (null, ?)",
-  /* BLOCK_SELECT */ "select block from %_segments where blockid = ?",
-  /* BLOCK_DELETE */ "delete from %_segments where blockid between ? and ?",
-  /* BLOCK_DELETE_ALL */ "delete from %_segments",
-
-  /* SEGDIR_MAX_INDEX */ "select max(idx) from %_segdir where level = ?",
-  /* SEGDIR_SET */ "insert into %_segdir values (?, ?, ?, ?, ?, ?)",
-  /* SEGDIR_SELECT_LEVEL */
-  "select start_block, leaves_end_block, root, idx from %_segdir "
-  " where level = ? order by idx",
-  /* SEGDIR_SPAN */
-  "select min(start_block), max(end_block) from %_segdir "
-  " where level = ? and start_block <> 0",
-  /* SEGDIR_DELETE */ "delete from %_segdir where level = ?",
-
-  /* NOTE(shess): The first three results of the following two
-  ** statements must match.
-  */
-  /* SEGDIR_SELECT_SEGMENT */
-  "select start_block, leaves_end_block, root from %_segdir "
-  " where level = ? and idx = ?",
-  /* SEGDIR_SELECT_ALL */
-  "select start_block, leaves_end_block, root from %_segdir "
-  " order by level desc, idx asc",
-  /* SEGDIR_DELETE_ALL */ "delete from %_segdir",
-  /* SEGDIR_COUNT */ "select count(*), ifnull(max(level),0) from %_segdir",
-};
-
-/*
-** A connection to a fulltext index is an instance of the following
-** structure.  The xCreate and xConnect methods create an instance
-** of this structure and xDestroy and xDisconnect free that instance.
-** All other methods receive a pointer to the structure as one of their
-** arguments.
-*/
-struct fulltext_vtab {
-  sqlite3_vtab base;               /* Base class used by SQLite core */
-  sqlite3 *db;                     /* The database connection */
-  const char *zDb;                 /* logical database name */
-  const char *zName;               /* virtual table name */
-  int nColumn;                     /* number of columns in virtual table */
-  char **azColumn;                 /* column names.  malloced */
-  char **azContentColumn;          /* column names in content table; malloced */
-  sqlite3_tokenizer *pTokenizer;   /* tokenizer for inserts and queries */
-
-  /* Precompiled statements which we keep as long as the table is
-  ** open.
-  */
-  sqlite3_stmt *pFulltextStatements[MAX_STMT];
-
-  /* Precompiled statements used for segment merges.  We run a
-  ** separate select across the leaf level of each tree being merged.
-  */
-  sqlite3_stmt *pLeafSelectStmts[MERGE_COUNT];
-  /* The statement used to prepare pLeafSelectStmts. */
-#define LEAF_SELECT \
-  "select block from %_segments where blockid between ? and ? order by blockid"
-
-  /* These buffer pending index updates during transactions.
-  ** nPendingData estimates the memory size of the pending data.  It
-  ** doesn't include the hash-bucket overhead, nor any malloc
-  ** overhead.  When nPendingData exceeds kPendingThreshold, the
-  ** buffer is flushed even before the transaction closes.
-  ** pendingTerms stores the data, and is only valid when nPendingData
-  ** is >=0 (nPendingData<0 means pendingTerms has not been
-  ** initialized).  iPrevDocid is the last docid written, used to make
-  ** certain we're inserting in sorted order.
-  */
-  int nPendingData;
-#define kPendingThreshold (1*1024*1024)
-  sqlite_int64 iPrevDocid;
-  fts3Hash pendingTerms;
-};
-
-/*
-** When the core wants to do a query, it create a cursor using a
-** call to xOpen.  This structure is an instance of a cursor.  It
-** is destroyed by xClose.
-*/
-typedef struct fulltext_cursor {
-  sqlite3_vtab_cursor base;        /* Base class used by SQLite core */
-  QueryType iCursorType;           /* Copy of sqlite3_index_info.idxNum */
-  sqlite3_stmt *pStmt;             /* Prepared statement in use by the cursor */
-  int eof;                         /* True if at End Of Results */
-  Fts3Expr *pExpr;                 /* Parsed MATCH query string */
-  Snippet snippet;                 /* Cached snippet for the current row */
-  int iColumn;                     /* Column being searched */
-  DataBuffer result;               /* Doclist results from fulltextQuery */
-  DLReader reader;                 /* Result reader if result not empty */
-} fulltext_cursor;
-
-static fulltext_vtab *cursor_vtab(fulltext_cursor *c){
-  return (fulltext_vtab *) c->base.pVtab;
-}
-
-static const sqlite3_module fts3Module;   /* forward declaration */
-
-/* Return a dynamically generated statement of the form
- *   insert into %_content (docid, ...) values (?, ...)
- */
-static const char *contentInsertStatement(fulltext_vtab *v){
-  StringBuffer sb;
-  int i;
-
-  initStringBuffer(&sb);
-  append(&sb, "insert into %_content (docid, ");
-  appendList(&sb, v->nColumn, v->azContentColumn);
-  append(&sb, ") values (?");
-  for(i=0; i<v->nColumn; ++i)
-    append(&sb, ", ?");
-  append(&sb, ")");
-  return stringBufferData(&sb);
-}
-
-/* Return a dynamically generated statement of the form
- *   select <content columns> from %_content where docid = ?
- */
-static const char *contentSelectStatement(fulltext_vtab *v){
-  StringBuffer sb;
-  initStringBuffer(&sb);
-  append(&sb, "SELECT ");
-  appendList(&sb, v->nColumn, v->azContentColumn);
-  append(&sb, " FROM %_content WHERE docid = ?");
-  return stringBufferData(&sb);
-}
-
-/* Return a dynamically generated statement of the form
- *   update %_content set [col_0] = ?, [col_1] = ?, ...
- *                    where docid = ?
- */
-static const char *contentUpdateStatement(fulltext_vtab *v){
-  StringBuffer sb;
-  int i;
-
-  initStringBuffer(&sb);
-  append(&sb, "update %_content set ");
-  for(i=0; i<v->nColumn; ++i) {
-    if( i>0 ){
-      append(&sb, ", ");
-    }
-    append(&sb, v->azContentColumn[i]);
-    append(&sb, " = ?");
-  }
-  append(&sb, " where docid = ?");
-  return stringBufferData(&sb);
-}
-
-/* Puts a freshly-prepared statement determined by iStmt in *ppStmt.
-** If the indicated statement has never been prepared, it is prepared
-** and cached, otherwise the cached version is reset.
-*/
-static int sql_get_statement(fulltext_vtab *v, fulltext_statement iStmt,
-                             sqlite3_stmt **ppStmt){
-  assert( iStmt<MAX_STMT );
-  if( v->pFulltextStatements[iStmt]==NULL ){
-    const char *zStmt;
-    int rc;
-    switch( iStmt ){
-      case CONTENT_INSERT_STMT:
-        zStmt = contentInsertStatement(v); break;
-      case CONTENT_SELECT_STMT:
-        zStmt = contentSelectStatement(v); break;
-      case CONTENT_UPDATE_STMT:
-        zStmt = contentUpdateStatement(v); break;
-      default:
-        zStmt = fulltext_zStatement[iStmt];
-    }
-    rc = sql_prepare(v->db, v->zDb, v->zName, &v->pFulltextStatements[iStmt],
-                         zStmt);
-    if( zStmt != fulltext_zStatement[iStmt]) sqlite3_free((void *) zStmt);
-    if( rc!=SQLITE_OK ) return rc;
-  } else {
-    int rc = sqlite3_reset(v->pFulltextStatements[iStmt]);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-
-  *ppStmt = v->pFulltextStatements[iStmt];
-  return SQLITE_OK;
-}
-
-/* Like sqlite3_step(), but convert SQLITE_DONE to SQLITE_OK and
-** SQLITE_ROW to SQLITE_ERROR.  Useful for statements like UPDATE,
-** where we expect no results.
-*/
-static int sql_single_step(sqlite3_stmt *s){
-  int rc = sqlite3_step(s);
-  return (rc==SQLITE_DONE) ? SQLITE_OK : rc;
-}
-
-/* Like sql_get_statement(), but for special replicated LEAF_SELECT
-** statements.  idx -1 is a special case for an uncached version of
-** the statement (used in the optimize implementation).
-*/
-/* TODO(shess) Write version for generic statements and then share
-** that between the cached-statement functions.
-*/
-static int sql_get_leaf_statement(fulltext_vtab *v, int idx,
-                                  sqlite3_stmt **ppStmt){
-  assert( idx>=-1 && idx<MERGE_COUNT );
-  if( idx==-1 ){
-    return sql_prepare(v->db, v->zDb, v->zName, ppStmt, LEAF_SELECT);
-  }else if( v->pLeafSelectStmts[idx]==NULL ){
-    int rc = sql_prepare(v->db, v->zDb, v->zName, &v->pLeafSelectStmts[idx],
-                         LEAF_SELECT);
-    if( rc!=SQLITE_OK ) return rc;
-  }else{
-    int rc = sqlite3_reset(v->pLeafSelectStmts[idx]);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-
-  *ppStmt = v->pLeafSelectStmts[idx];
-  return SQLITE_OK;
-}
-
-/* insert into %_content (docid, ...) values ([docid], [pValues])
-** If the docid contains SQL NULL, then a unique docid will be
-** generated.
-*/
-static int content_insert(fulltext_vtab *v, sqlite3_value *docid,
-                          sqlite3_value **pValues){
-  sqlite3_stmt *s;
-  int i;
-  int rc = sql_get_statement(v, CONTENT_INSERT_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_value(s, 1, docid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  for(i=0; i<v->nColumn; ++i){
-    rc = sqlite3_bind_value(s, 2+i, pValues[i]);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-
-  return sql_single_step(s);
-}
-
-/* update %_content set col0 = pValues[0], col1 = pValues[1], ...
- *                  where docid = [iDocid] */
-static int content_update(fulltext_vtab *v, sqlite3_value **pValues,
-                          sqlite_int64 iDocid){
-  sqlite3_stmt *s;
-  int i;
-  int rc = sql_get_statement(v, CONTENT_UPDATE_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  for(i=0; i<v->nColumn; ++i){
-    rc = sqlite3_bind_value(s, 1+i, pValues[i]);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-
-  rc = sqlite3_bind_int64(s, 1+v->nColumn, iDocid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return sql_single_step(s);
-}
-
-static void freeStringArray(int nString, const char **pString){
-  int i;
-
-  for (i=0 ; i < nString ; ++i) {
-    if( pString[i]!=NULL ) sqlite3_free((void *) pString[i]);
-  }
-  sqlite3_free((void *) pString);
-}
-
-/* select * from %_content where docid = [iDocid]
- * The caller must delete the returned array and all strings in it.
- * null fields will be NULL in the returned array.
- *
- * TODO: Perhaps we should return pointer/length strings here for consistency
- * with other code which uses pointer/length. */
-static int content_select(fulltext_vtab *v, sqlite_int64 iDocid,
-                          const char ***pValues){
-  sqlite3_stmt *s;
-  const char **values;
-  int i;
-  int rc;
-
-  *pValues = NULL;
-
-  rc = sql_get_statement(v, CONTENT_SELECT_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 1, iDocid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_step(s);
-  if( rc!=SQLITE_ROW ) return rc;
-
-  values = (const char **) sqlite3_malloc(v->nColumn * sizeof(const char *));
-  for(i=0; i<v->nColumn; ++i){
-    if( sqlite3_column_type(s, i)==SQLITE_NULL ){
-      values[i] = NULL;
-    }else{
-      values[i] = string_dup((char*)sqlite3_column_text(s, i));
-    }
-  }
-
-  /* We expect only one row.  We must execute another sqlite3_step()
-   * to complete the iteration; otherwise the table will remain locked. */
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_DONE ){
-    *pValues = values;
-    return SQLITE_OK;
-  }
-
-  freeStringArray(v->nColumn, values);
-  return rc;
-}
-
-/* delete from %_content where docid = [iDocid ] */
-static int content_delete(fulltext_vtab *v, sqlite_int64 iDocid){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, CONTENT_DELETE_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 1, iDocid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return sql_single_step(s);
-}
-
-/* Returns SQLITE_ROW if any rows exist in %_content, SQLITE_DONE if
-** no rows exist, and any error in case of failure.
-*/
-static int content_exists(fulltext_vtab *v){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, CONTENT_EXISTS_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_step(s);
-  if( rc!=SQLITE_ROW ) return rc;
-
-  /* We expect only one row.  We must execute another sqlite3_step()
-   * to complete the iteration; otherwise the table will remain locked. */
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_DONE ) return SQLITE_ROW;
-  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
-  return rc;
-}
-
-/* insert into %_segments values ([pData])
-**   returns assigned blockid in *piBlockid
-*/
-static int block_insert(fulltext_vtab *v, const char *pData, int nData,
-                        sqlite_int64 *piBlockid){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, BLOCK_INSERT_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_blob(s, 1, pData, nData, SQLITE_STATIC);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
-  if( rc!=SQLITE_DONE ) return rc;
-
-  /* blockid column is an alias for rowid. */
-  *piBlockid = sqlite3_last_insert_rowid(v->db);
-  return SQLITE_OK;
-}
-
-/* delete from %_segments
-**   where blockid between [iStartBlockid] and [iEndBlockid]
-**
-** Deletes the range of blocks, inclusive, used to delete the blocks
-** which form a segment.
-*/
-static int block_delete(fulltext_vtab *v,
-                        sqlite_int64 iStartBlockid, sqlite_int64 iEndBlockid){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, BLOCK_DELETE_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 1, iStartBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 2, iEndBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return sql_single_step(s);
-}
-
-/* Returns SQLITE_ROW with *pidx set to the maximum segment idx found
-** at iLevel.  Returns SQLITE_DONE if there are no segments at
-** iLevel.  Otherwise returns an error.
-*/
-static int segdir_max_index(fulltext_vtab *v, int iLevel, int *pidx){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, SEGDIR_MAX_INDEX_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int(s, 1, iLevel);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_step(s);
-  /* Should always get at least one row due to how max() works. */
-  if( rc==SQLITE_DONE ) return SQLITE_DONE;
-  if( rc!=SQLITE_ROW ) return rc;
-
-  /* NULL means that there were no inputs to max(). */
-  if( SQLITE_NULL==sqlite3_column_type(s, 0) ){
-    rc = sqlite3_step(s);
-    if( rc==SQLITE_ROW ) return SQLITE_ERROR;
-    return rc;
-  }
-
-  *pidx = sqlite3_column_int(s, 0);
-
-  /* We expect only one row.  We must execute another sqlite3_step()
-   * to complete the iteration; otherwise the table will remain locked. */
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
-  if( rc!=SQLITE_DONE ) return rc;
-  return SQLITE_ROW;
-}
-
-/* insert into %_segdir values (
-**   [iLevel], [idx],
-**   [iStartBlockid], [iLeavesEndBlockid], [iEndBlockid],
-**   [pRootData]
-** )
-*/
-static int segdir_set(fulltext_vtab *v, int iLevel, int idx,
-                      sqlite_int64 iStartBlockid,
-                      sqlite_int64 iLeavesEndBlockid,
-                      sqlite_int64 iEndBlockid,
-                      const char *pRootData, int nRootData){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, SEGDIR_SET_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int(s, 1, iLevel);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int(s, 2, idx);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 3, iStartBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 4, iLeavesEndBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 5, iEndBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_blob(s, 6, pRootData, nRootData, SQLITE_STATIC);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return sql_single_step(s);
-}
-
-/* Queries %_segdir for the block span of the segments in level
-** iLevel.  Returns SQLITE_DONE if there are no blocks for iLevel,
-** SQLITE_ROW if there are blocks, else an error.
-*/
-static int segdir_span(fulltext_vtab *v, int iLevel,
-                       sqlite_int64 *piStartBlockid,
-                       sqlite_int64 *piEndBlockid){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, SEGDIR_SPAN_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int(s, 1, iLevel);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_DONE ) return SQLITE_DONE;  /* Should never happen */
-  if( rc!=SQLITE_ROW ) return rc;
-
-  /* This happens if all segments at this level are entirely inline. */
-  if( SQLITE_NULL==sqlite3_column_type(s, 0) ){
-    /* We expect only one row.  We must execute another sqlite3_step()
-     * to complete the iteration; otherwise the table will remain locked. */
-    int rc2 = sqlite3_step(s);
-    if( rc2==SQLITE_ROW ) return SQLITE_ERROR;
-    return rc2;
-  }
-
-  *piStartBlockid = sqlite3_column_int64(s, 0);
-  *piEndBlockid = sqlite3_column_int64(s, 1);
-
-  /* We expect only one row.  We must execute another sqlite3_step()
-   * to complete the iteration; otherwise the table will remain locked. */
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
-  if( rc!=SQLITE_DONE ) return rc;
-  return SQLITE_ROW;
-}
-
-/* Delete the segment blocks and segment directory records for all
-** segments at iLevel.
-*/
-static int segdir_delete(fulltext_vtab *v, int iLevel){
-  sqlite3_stmt *s;
-  sqlite_int64 iStartBlockid, iEndBlockid;
-  int rc = segdir_span(v, iLevel, &iStartBlockid, &iEndBlockid);
-  if( rc!=SQLITE_ROW && rc!=SQLITE_DONE ) return rc;
-
-  if( rc==SQLITE_ROW ){
-    rc = block_delete(v, iStartBlockid, iEndBlockid);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-
-  /* Delete the segment directory itself. */
-  rc = sql_get_statement(v, SEGDIR_DELETE_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 1, iLevel);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return sql_single_step(s);
-}
-
-/* Delete entire fts index, SQLITE_OK on success, relevant error on
-** failure.
-*/
-static int segdir_delete_all(fulltext_vtab *v){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, SEGDIR_DELETE_ALL_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sql_single_step(s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sql_get_statement(v, BLOCK_DELETE_ALL_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return sql_single_step(s);
-}
-
-/* Returns SQLITE_OK with *pnSegments set to the number of entries in
-** %_segdir and *piMaxLevel set to the highest level which has a
-** segment.  Otherwise returns the SQLite error which caused failure.
-*/
-static int segdir_count(fulltext_vtab *v, int *pnSegments, int *piMaxLevel){
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, SEGDIR_COUNT_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_step(s);
-  /* TODO(shess): This case should not be possible?  Should stronger
-  ** measures be taken if it happens?
-  */
-  if( rc==SQLITE_DONE ){
-    *pnSegments = 0;
-    *piMaxLevel = 0;
-    return SQLITE_OK;
-  }
-  if( rc!=SQLITE_ROW ) return rc;
-
-  *pnSegments = sqlite3_column_int(s, 0);
-  *piMaxLevel = sqlite3_column_int(s, 1);
-
-  /* We expect only one row.  We must execute another sqlite3_step()
-   * to complete the iteration; otherwise the table will remain locked. */
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_DONE ) return SQLITE_OK;
-  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
-  return rc;
-}
-
-/* TODO(shess) clearPendingTerms() is far down the file because
-** writeZeroSegment() is far down the file because LeafWriter is far
-** down the file.  Consider refactoring the code to move the non-vtab
-** code above the vtab code so that we don't need this forward
-** reference.
-*/
-static int clearPendingTerms(fulltext_vtab *v);
-
-/*
-** Free the memory used to contain a fulltext_vtab structure.
-*/
-static void fulltext_vtab_destroy(fulltext_vtab *v){
-  int iStmt, i;
-
-  FTSTRACE(("FTS3 Destroy %p\n", v));
-  for( iStmt=0; iStmt<MAX_STMT; iStmt++ ){
-    if( v->pFulltextStatements[iStmt]!=NULL ){
-      sqlite3_finalize(v->pFulltextStatements[iStmt]);
-      v->pFulltextStatements[iStmt] = NULL;
-    }
-  }
-
-  for( i=0; i<MERGE_COUNT; i++ ){
-    if( v->pLeafSelectStmts[i]!=NULL ){
-      sqlite3_finalize(v->pLeafSelectStmts[i]);
-      v->pLeafSelectStmts[i] = NULL;
-    }
-  }
-
-  if( v->pTokenizer!=NULL ){
-    v->pTokenizer->pModule->xDestroy(v->pTokenizer);
-    v->pTokenizer = NULL;
-  }
-
-  clearPendingTerms(v);
-
-  sqlite3_free(v->azColumn);
-  for(i = 0; i < v->nColumn; ++i) {
-    sqlite3_free(v->azContentColumn[i]);
-  }
-  sqlite3_free(v->azContentColumn);
-  sqlite3_free(v);
-}
-
-/*
-** Token types for parsing the arguments to xConnect or xCreate.
-*/
-#define TOKEN_EOF         0    /* End of file */
-#define TOKEN_SPACE       1    /* Any kind of whitespace */
-#define TOKEN_ID          2    /* An identifier */
-#define TOKEN_STRING      3    /* A string literal */
-#define TOKEN_PUNCT       4    /* A single punctuation character */
-
-/*
-** If X is a character that can be used in an identifier then
-** ftsIdChar(X) will be true.  Otherwise it is false.
-**
-** For ASCII, any character with the high-order bit set is
-** allowed in an identifier.  For 7-bit characters, 
-** isFtsIdChar[X] must be 1.
-**
-** Ticket #1066.  the SQL standard does not allow '$' in the
-** middle of identfiers.  But many SQL implementations do. 
-** SQLite will allow '$' in identifiers for compatibility.
-** But the feature is undocumented.
-*/
-static const char isFtsIdChar[] = {
-/* x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 xA xB xC xD xE xF */
-    0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,  /* 2x */
-    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0,  /* 3x */
-    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  /* 4x */
-    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1,  /* 5x */
-    0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  /* 6x */
-    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0,  /* 7x */
-};
-#define ftsIdChar(C)  (((c=C)&0x80)!=0 || (c>0x1f && isFtsIdChar[c-0x20]))
-
-
-/*
-** Return the length of the token that begins at z[0]. 
-** Store the token type in *tokenType before returning.
-*/
-static int ftsGetToken(const char *z, int *tokenType){
-  int i, c;
-  switch( *z ){
-    case 0: {
-      *tokenType = TOKEN_EOF;
-      return 0;
-    }
-    case ' ': case '\t': case '\n': case '\f': case '\r': {
-      for(i=1; safe_isspace(z[i]); i++){}
-      *tokenType = TOKEN_SPACE;
-      return i;
-    }
-    case '`':
-    case '\'':
-    case '"': {
-      int delim = z[0];
-      for(i=1; (c=z[i])!=0; i++){
-        if( c==delim ){
-          if( z[i+1]==delim ){
-            i++;
-          }else{
-            break;
-          }
-        }
-      }
-      *tokenType = TOKEN_STRING;
-      return i + (c!=0);
-    }
-    case '[': {
-      for(i=1, c=z[0]; c!=']' && (c=z[i])!=0; i++){}
-      *tokenType = TOKEN_ID;
-      return i;
-    }
-    default: {
-      if( !ftsIdChar(*z) ){
-        break;
-      }
-      for(i=1; ftsIdChar(z[i]); i++){}
-      *tokenType = TOKEN_ID;
-      return i;
-    }
-  }
-  *tokenType = TOKEN_PUNCT;
-  return 1;
-}
-
-/*
-** A token extracted from a string is an instance of the following
-** structure.
-*/
-typedef struct FtsToken {
-  const char *z;       /* Pointer to token text.  Not '\000' terminated */
-  short int n;         /* Length of the token text in bytes. */
-} FtsToken;
-
-/*
-** Given a input string (which is really one of the argv[] parameters
-** passed into xConnect or xCreate) split the string up into tokens.
-** Return an array of pointers to '\000' terminated strings, one string
-** for each non-whitespace token.
-**
-** The returned array is terminated by a single NULL pointer.
-**
-** Space to hold the returned array is obtained from a single
-** malloc and should be freed by passing the return value to free().
-** The individual strings within the token list are all a part of
-** the single memory allocation and will all be freed at once.
-*/
-static char **tokenizeString(const char *z, int *pnToken){
-  int nToken = 0;
-  FtsToken *aToken = sqlite3_malloc( strlen(z) * sizeof(aToken[0]) );
-  int n = 1;
-  int e, i;
-  int totalSize = 0;
-  char **azToken;
-  char *zCopy;
-  while( n>0 ){
-    n = ftsGetToken(z, &e);
-    if( e!=TOKEN_SPACE ){
-      aToken[nToken].z = z;
-      aToken[nToken].n = n;
-      nToken++;
-      totalSize += n+1;
-    }
-    z += n;
-  }
-  azToken = (char**)sqlite3_malloc( nToken*sizeof(char*) + totalSize );
-  zCopy = (char*)&azToken[nToken];
-  nToken--;
-  for(i=0; i<nToken; i++){
-    azToken[i] = zCopy;
-    n = aToken[i].n;
-    memcpy(zCopy, aToken[i].z, n);
-    zCopy[n] = 0;
-    zCopy += n+1;
-  }
-  azToken[nToken] = 0;
-  sqlite3_free(aToken);
-  *pnToken = nToken;
-  return azToken;
+/*
+** Return the number of bytes required to encode v as a varint
+*/
+int sqlite3Fts3VarintLen(sqlite3_uint64 v){
+  int i = 0;
+  do{
+    i++;
+    v >>= 7;
+  }while( v!=0 );
+  return i;
 }
 
 /*
 ** Convert an SQL-style quoted string into a normal string by removing
 ** the quote characters.  The conversion is done in-place.  If the
 ** input does not begin with a quote character, then this routine
 ** is a no-op.
 **
 ** Examples:
 **
 **     "abc"   becomes   abc
 **     'xyz'   becomes   xyz
 **     [pqr]   becomes   pqr
 **     `mno`   becomes   mno
-*/
-static void dequoteString(char *z){
-  int quote;
-  int i, j;
-  if( z==0 ) return;
+**
+*/
+void sqlite3Fts3Dequote(char *z){
+  char quote;                     /* Quote character (if any ) */
+
   quote = z[0];
-  switch( quote ){
-    case '\'':  break;
-    case '"':   break;
-    case '`':   break;                /* For MySQL compatibility */
-    case '[':   quote = ']';  break;  /* For MS SqlServer compatibility */
-    default:    return;
-  }
-  for(i=1, j=0; z[i]; i++){
-    if( z[i]==quote ){
-      if( z[i+1]==quote ){
-        z[j++] = quote;
-        i++;
+  if( quote=='[' || quote=='\'' || quote=='"' || quote=='`' ){
+    int iIn = 1;                  /* Index of next byte to read from input */
+    int iOut = 0;                 /* Index of next byte to write to output */
+
+    /* If the first byte was a '[', then the close-quote character is a ']' */
+    if( quote=='[' ) quote = ']';  
+
+    while( ALWAYS(z[iIn]) ){
+      if( z[iIn]==quote ){
+        if( z[iIn+1]!=quote ) break;
+        z[iOut++] = quote;
+        iIn += 2;
       }else{
-        z[j++] = 0;
+        z[iOut++] = z[iIn++];
+      }
+    }
+    z[iOut] = '\0';
+  }
+}
+
+/*
+** Read a single varint from the doclist at *pp and advance *pp to point
+** to the first byte past the end of the varint.  Add the value of the varint
+** to *pVal.
+*/
+static void fts3GetDeltaVarint(char **pp, sqlite3_int64 *pVal){
+  sqlite3_int64 iVal;
+  *pp += sqlite3Fts3GetVarint(*pp, &iVal);
+  *pVal += iVal;
+}
+
+/*
+** As long as *pp has not reached its end (pEnd), then do the same
+** as fts3GetDeltaVarint(): read a single varint and add it to *pVal.
+** But if we have reached the end of the varint, just set *pp=0 and
+** leave *pVal unchanged.
+*/
+static void fts3GetDeltaVarint2(char **pp, char *pEnd, sqlite3_int64 *pVal){
+  if( *pp>=pEnd ){
+    *pp = 0;
+  }else{
+    fts3GetDeltaVarint(pp, pVal);
+  }
+}
+
+/*
+** The xDisconnect() virtual table method.
+*/
+static int fts3DisconnectMethod(sqlite3_vtab *pVtab){
+  Fts3Table *p = (Fts3Table *)pVtab;
+  int i;
+
+  assert( p->nPendingData==0 );
+  assert( p->pSegments==0 );
+
+  /* Free any prepared statements held */
+  for(i=0; i<SizeofArray(p->aStmt); i++){
+    sqlite3_finalize(p->aStmt[i]);
+  }
+  sqlite3_free(p->zSegmentsTbl);
+  sqlite3_free(p->zReadExprlist);
+  sqlite3_free(p->zWriteExprlist);
+
+  /* Invoke the tokenizer destructor to free the tokenizer. */
+  p->pTokenizer->pModule->xDestroy(p->pTokenizer);
+
+  sqlite3_free(p);
+  return SQLITE_OK;
+}
+
+/*
+** Construct one or more SQL statements from the format string given
+** and then evaluate those statements. The success code is written
+** into *pRc.
+**
+** If *pRc is initially non-zero then this routine is a no-op.
+*/
+static void fts3DbExec(
+  int *pRc,              /* Success code */
+  sqlite3 *db,           /* Database in which to run SQL */
+  const char *zFormat,   /* Format string for SQL */
+  ...                    /* Arguments to the format string */
+){
+  va_list ap;
+  char *zSql;
+  if( *pRc ) return;
+  va_start(ap, zFormat);
+  zSql = sqlite3_vmprintf(zFormat, ap);
+  va_end(ap);
+  if( zSql==0 ){
+    *pRc = SQLITE_NOMEM;
+  }else{
+    *pRc = sqlite3_exec(db, zSql, 0, 0, 0);
+    sqlite3_free(zSql);
+  }
+}
+
+/*
+** The xDestroy() virtual table method.
+*/
+static int fts3DestroyMethod(sqlite3_vtab *pVtab){
+  int rc = SQLITE_OK;              /* Return code */
+  Fts3Table *p = (Fts3Table *)pVtab;
+  sqlite3 *db = p->db;
+
+  /* Drop the shadow tables */
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_content'", p->zDb, p->zName);
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_segments'", p->zDb,p->zName);
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_segdir'", p->zDb, p->zName);
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_docsize'", p->zDb, p->zName);
+  fts3DbExec(&rc, db, "DROP TABLE IF EXISTS %Q.'%q_stat'", p->zDb, p->zName);
+
+  /* If everything has worked, invoke fts3DisconnectMethod() to free the
+  ** memory associated with the Fts3Table structure and return SQLITE_OK.
+  ** Otherwise, return an SQLite error code.
+  */
+  return (rc==SQLITE_OK ? fts3DisconnectMethod(pVtab) : rc);
+}
+
+
+/*
+** Invoke sqlite3_declare_vtab() to declare the schema for the FTS3 table
+** passed as the first argument. This is done as part of the xConnect()
+** and xCreate() methods.
+**
+** If *pRc is non-zero when this function is called, it is a no-op. 
+** Otherwise, if an error occurs, an SQLite error code is stored in *pRc
+** before returning.
+*/
+static void fts3DeclareVtab(int *pRc, Fts3Table *p){
+  if( *pRc==SQLITE_OK ){
+    int i;                        /* Iterator variable */
+    int rc;                       /* Return code */
+    char *zSql;                   /* SQL statement passed to declare_vtab() */
+    char *zCols;                  /* List of user defined columns */
+
+    /* Create a list of user columns for the virtual table */
+    zCols = sqlite3_mprintf("%Q, ", p->azColumn[0]);
+    for(i=1; zCols && i<p->nColumn; i++){
+      zCols = sqlite3_mprintf("%z%Q, ", zCols, p->azColumn[i]);
+    }
+
+    /* Create the whole "CREATE TABLE" statement to pass to SQLite */
+    zSql = sqlite3_mprintf(
+        "CREATE TABLE x(%s %Q HIDDEN, docid HIDDEN)", zCols, p->zName
+    );
+    if( !zCols || !zSql ){
+      rc = SQLITE_NOMEM;
+    }else{
+      rc = sqlite3_declare_vtab(p->db, zSql);
+    }
+
+    sqlite3_free(zSql);
+    sqlite3_free(zCols);
+    *pRc = rc;
+  }
+}
+
+/*
+** Create the backing store tables (%_content, %_segments and %_segdir)
+** required by the FTS3 table passed as the only argument. This is done
+** as part of the vtab xCreate() method.
+**
+** If the p->bHasDocsize boolean is true (indicating that this is an
+** FTS4 table, not an FTS3 table) then also create the %_docsize and
+** %_stat tables required by FTS4.
+*/
+static int fts3CreateTables(Fts3Table *p){
+  int rc = SQLITE_OK;             /* Return code */
+  int i;                          /* Iterator variable */
+  char *zContentCols;             /* Columns of %_content table */
+  sqlite3 *db = p->db;            /* The database connection */
+
+  /* Create a list of user columns for the content table */
+  zContentCols = sqlite3_mprintf("docid INTEGER PRIMARY KEY");
+  for(i=0; zContentCols && i<p->nColumn; i++){
+    char *z = p->azColumn[i];
+    zContentCols = sqlite3_mprintf("%z, 'c%d%q'", zContentCols, i, z);
+  }
+  if( zContentCols==0 ) rc = SQLITE_NOMEM;
+
+  /* Create the content table */
+  fts3DbExec(&rc, db, 
+     "CREATE TABLE %Q.'%q_content'(%s)",
+     p->zDb, p->zName, zContentCols
+  );
+  sqlite3_free(zContentCols);
+  /* Create other tables */
+  fts3DbExec(&rc, db, 
+      "CREATE TABLE %Q.'%q_segments'(blockid INTEGER PRIMARY KEY, block BLOB);",
+      p->zDb, p->zName
+  );
+  fts3DbExec(&rc, db, 
+      "CREATE TABLE %Q.'%q_segdir'("
+        "level INTEGER,"
+        "idx INTEGER,"
+        "start_block INTEGER,"
+        "leaves_end_block INTEGER,"
+        "end_block INTEGER,"
+        "root BLOB,"
+        "PRIMARY KEY(level, idx)"
+      ");",
+      p->zDb, p->zName
+  );
+  if( p->bHasDocsize ){
+    fts3DbExec(&rc, db, 
+        "CREATE TABLE %Q.'%q_docsize'(docid INTEGER PRIMARY KEY, size BLOB);",
+        p->zDb, p->zName
+    );
+  }
+  if( p->bHasStat ){
+    fts3DbExec(&rc, db, 
+        "CREATE TABLE %Q.'%q_stat'(id INTEGER PRIMARY KEY, value BLOB);",
+        p->zDb, p->zName
+    );
+  }
+  return rc;
+}
+
+/*
+** Store the current database page-size in bytes in p->nPgsz.
+**
+** If *pRc is non-zero when this function is called, it is a no-op. 
+** Otherwise, if an error occurs, an SQLite error code is stored in *pRc
+** before returning.
+*/
+static void fts3DatabasePageSize(int *pRc, Fts3Table *p){
+  if( *pRc==SQLITE_OK ){
+    int rc;                       /* Return code */
+    char *zSql;                   /* SQL text "PRAGMA %Q.page_size" */
+    sqlite3_stmt *pStmt;          /* Compiled "PRAGMA %Q.page_size" statement */
+  
+    zSql = sqlite3_mprintf("PRAGMA %Q.page_size", p->zDb);
+    if( !zSql ){
+      rc = SQLITE_NOMEM;
+    }else{
+      rc = sqlite3_prepare(p->db, zSql, -1, &pStmt, 0);
+      if( rc==SQLITE_OK ){
+        sqlite3_step(pStmt);
+        p->nPgsz = sqlite3_column_int(pStmt, 0);
+        rc = sqlite3_finalize(pStmt);
+      }
+    }
+    assert( p->nPgsz>0 || rc!=SQLITE_OK );
+    sqlite3_free(zSql);
+    *pRc = rc;
+  }
+}
+
+/*
+** "Special" FTS4 arguments are column specifications of the following form:
+**
+**   <key> = <value>
+**
+** There may not be whitespace surrounding the "=" character. The <value> 
+** term may be quoted, but the <key> may not.
+*/
+static int fts3IsSpecialColumn(
+  const char *z, 
+  int *pnKey,
+  char **pzValue
+){
+  char *zValue;
+  const char *zCsr = z;
+
+  while( *zCsr!='=' ){
+    if( *zCsr=='\0' ) return 0;
+    zCsr++;
+  }
+
+  *pnKey = (int)(zCsr-z);
+  zValue = sqlite3_mprintf("%s", &zCsr[1]);
+  if( zValue ){
+    sqlite3Fts3Dequote(zValue);
+  }
+  *pzValue = zValue;
+  return 1;
+}
+
+/*
+** Append the output of a printf() style formatting to an existing string.
+*/
+static void fts3Appendf(
+  int *pRc,                       /* IN/OUT: Error code */
+  char **pz,                      /* IN/OUT: Pointer to string buffer */
+  const char *zFormat,            /* Printf format string to append */
+  ...                             /* Arguments for printf format string */
+){
+  if( *pRc==SQLITE_OK ){
+    va_list ap;
+    char *z;
+    va_start(ap, zFormat);
+    z = sqlite3_vmprintf(zFormat, ap);
+    if( z && *pz ){
+      char *z2 = sqlite3_mprintf("%s%s", *pz, z);
+      sqlite3_free(z);
+      z = z2;
+    }
+    if( z==0 ) *pRc = SQLITE_NOMEM;
+    sqlite3_free(*pz);
+    *pz = z;
+  }
+}
+
+/*
+** Return a copy of input string zInput enclosed in double-quotes (") and
+** with all double quote characters escaped. For example:
+**
+**     fts3QuoteId("un \"zip\"")   ->    "un \"\"zip\"\""
+**
+** The pointer returned points to memory obtained from sqlite3_malloc(). It
+** is the callers responsibility to call sqlite3_free() to release this
+** memory.
+*/
+static char *fts3QuoteId(char const *zInput){
+  int nRet;
+  char *zRet;
+  nRet = 2 + strlen(zInput)*2 + 1;
+  zRet = sqlite3_malloc(nRet);
+  if( zRet ){
+    int i;
+    char *z = zRet;
+    *(z++) = '"';
+    for(i=0; zInput[i]; i++){
+      if( zInput[i]=='"' ) *(z++) = '"';
+      *(z++) = zInput[i];
+    }
+    *(z++) = '"';
+    *(z++) = '\0';
+  }
+  return zRet;
+}
+
+/*
+** Return a list of comma separated SQL expressions that could be used
+** in a SELECT statement such as the following:
+**
+**     SELECT <list of expressions> FROM %_content AS x ...
+**
+** to return the docid, followed by each column of text data in order
+** from left to write. If parameter zFunc is not NULL, then instead of
+** being returned directly each column of text data is passed to an SQL
+** function named zFunc first. For example, if zFunc is "unzip" and the
+** table has the three user-defined columns "a", "b", and "c", the following
+** string is returned:
+**
+**     "docid, unzip(x.'a'), unzip(x.'b'), unzip(x.'c')"
+**
+** The pointer returned points to a buffer allocated by sqlite3_malloc(). It
+** is the responsibility of the caller to eventually free it.
+**
+** If *pRc is not SQLITE_OK when this function is called, it is a no-op (and
+** a NULL pointer is returned). Otherwise, if an OOM error is encountered
+** by this function, NULL is returned and *pRc is set to SQLITE_NOMEM. If
+** no error occurs, *pRc is left unmodified.
+*/
+static char *fts3ReadExprList(Fts3Table *p, const char *zFunc, int *pRc){
+  char *zRet = 0;
+  char *zFree = 0;
+  char *zFunction;
+  int i;
+
+  if( !zFunc ){
+    zFunction = "";
+  }else{
+    zFree = zFunction = fts3QuoteId(zFunc);
+  }
+  fts3Appendf(pRc, &zRet, "docid");
+  for(i=0; i<p->nColumn; i++){
+    fts3Appendf(pRc, &zRet, ",%s(x.'c%d%q')", zFunction, i, p->azColumn[i]);
+  }
+  sqlite3_free(zFree);
+  return zRet;
+}
+
+/*
+** Return a list of N comma separated question marks, where N is the number
+** of columns in the %_content table (one for the docid plus one for each
+** user-defined text column).
+**
+** If argument zFunc is not NULL, then all but the first question mark
+** is preceded by zFunc and an open bracket, and followed by a closed
+** bracket. For example, if zFunc is "zip" and the FTS3 table has three 
+** user-defined text columns, the following string is returned:
+**
+**     "?, zip(?), zip(?), zip(?)"
+**
+** The pointer returned points to a buffer allocated by sqlite3_malloc(). It
+** is the responsibility of the caller to eventually free it.
+**
+** If *pRc is not SQLITE_OK when this function is called, it is a no-op (and
+** a NULL pointer is returned). Otherwise, if an OOM error is encountered
+** by this function, NULL is returned and *pRc is set to SQLITE_NOMEM. If
+** no error occurs, *pRc is left unmodified.
+*/
+static char *fts3WriteExprList(Fts3Table *p, const char *zFunc, int *pRc){
+  char *zRet = 0;
+  char *zFree = 0;
+  char *zFunction;
+  int i;
+
+  if( !zFunc ){
+    zFunction = "";
+  }else{
+    zFree = zFunction = fts3QuoteId(zFunc);
+  }
+  fts3Appendf(pRc, &zRet, "?");
+  for(i=0; i<p->nColumn; i++){
+    fts3Appendf(pRc, &zRet, ",%s(?)", zFunction);
+  }
+  sqlite3_free(zFree);
+  return zRet;
+}
+
+/*
+** This function is the implementation of both the xConnect and xCreate
+** methods of the FTS3 virtual table.
+**
+** The argv[] array contains the following:
+**
+**   argv[0]   -> module name  ("fts3" or "fts4")
+**   argv[1]   -> database name
+**   argv[2]   -> table name
+**   argv[...] -> "column name" and other module argument fields.
+*/
+static int fts3InitVtab(
+  int isCreate,                   /* True for xCreate, false for xConnect */
+  sqlite3 *db,                    /* The SQLite database connection */
+  void *pAux,                     /* Hash table containing tokenizers */
+  int argc,                       /* Number of elements in argv array */
+  const char * const *argv,       /* xCreate/xConnect argument array */
+  sqlite3_vtab **ppVTab,          /* Write the resulting vtab structure here */
+  char **pzErr                    /* Write any error message here */
+){
+  Fts3Hash *pHash = (Fts3Hash *)pAux;
+  Fts3Table *p = 0;               /* Pointer to allocated vtab */
+  int rc = SQLITE_OK;             /* Return code */
+  int i;                          /* Iterator variable */
+  int nByte;                      /* Size of allocation used for *p */
+  int iCol;                       /* Column index */
+  int nString = 0;                /* Bytes required to hold all column names */
+  int nCol = 0;                   /* Number of columns in the FTS table */
+  char *zCsr;                     /* Space for holding column names */
+  int nDb;                        /* Bytes required to hold database name */
+  int nName;                      /* Bytes required to hold table name */
+  int isFts4 = (argv[0][3]=='4'); /* True for FTS4, false for FTS3 */
+  int bNoDocsize = 0;             /* True to omit %_docsize table */
+  const char **aCol;              /* Array of column names */
+  sqlite3_tokenizer *pTokenizer = 0;        /* Tokenizer for this table */
+
+  char *zCompress = 0;
+  char *zUncompress = 0;
+
+  assert( strlen(argv[0])==4 );
+  assert( (sqlite3_strnicmp(argv[0], "fts4", 4)==0 && isFts4)
+       || (sqlite3_strnicmp(argv[0], "fts3", 4)==0 && !isFts4)
+  );
+
+  nDb = (int)strlen(argv[1]) + 1;
+  nName = (int)strlen(argv[2]) + 1;
+
+  aCol = (const char **)sqlite3_malloc(sizeof(const char *) * (argc-2) );
+  if( !aCol ) return SQLITE_NOMEM;
+  memset((void *)aCol, 0, sizeof(const char *) * (argc-2));
+
+  /* Loop through all of the arguments passed by the user to the FTS3/4
+  ** module (i.e. all the column names and special arguments). This loop
+  ** does the following:
+  **
+  **   + Figures out the number of columns the FTSX table will have, and
+  **     the number of bytes of space that must be allocated to store copies
+  **     of the column names.
+  **
+  **   + If there is a tokenizer specification included in the arguments,
+  **     initializes the tokenizer pTokenizer.
+  */
+  for(i=3; rc==SQLITE_OK && i<argc; i++){
+    char const *z = argv[i];
+    int nKey;
+    char *zVal;
+
+    /* Check if this is a tokenizer specification */
+    if( !pTokenizer 
+     && strlen(z)>8
+     && 0==sqlite3_strnicmp(z, "tokenize", 8) 
+     && 0==sqlite3Fts3IsIdChar(z[8])
+    ){
+      rc = sqlite3Fts3InitTokenizer(pHash, &z[9], &pTokenizer, pzErr);
+    }
+
+    /* Check if it is an FTS4 special argument. */
+    else if( isFts4 && fts3IsSpecialColumn(z, &nKey, &zVal) ){
+      if( !zVal ){
+        rc = SQLITE_NOMEM;
+        goto fts3_init_out;
+      }
+      if( nKey==9 && 0==sqlite3_strnicmp(z, "matchinfo", 9) ){
+        if( strlen(zVal)==4 && 0==sqlite3_strnicmp(zVal, "fts3", 4) ){
+          bNoDocsize = 1;
+        }else{
+          *pzErr = sqlite3_mprintf("unrecognized matchinfo: %s", zVal);
+          rc = SQLITE_ERROR;
+        }
+      }else if( nKey==8 && 0==sqlite3_strnicmp(z, "compress", 8) ){
+        zCompress = zVal;
+        zVal = 0;
+      }else if( nKey==10 && 0==sqlite3_strnicmp(z, "uncompress", 10) ){
+        zUncompress = zVal;
+        zVal = 0;
+      }else{
+        *pzErr = sqlite3_mprintf("unrecognized parameter: %s", z);
+        rc = SQLITE_ERROR;
+      }
+      sqlite3_free(zVal);
+    }
+
+    /* Otherwise, the argument is a column name. */
+    else {
+      nString += (int)(strlen(z) + 1);
+      aCol[nCol++] = z;
+    }
+  }
+  if( rc!=SQLITE_OK ) goto fts3_init_out;
+
+  if( nCol==0 ){
+    assert( nString==0 );
+    aCol[0] = "content";
+    nString = 8;
+    nCol = 1;
+  }
+
+  if( pTokenizer==0 ){
+    rc = sqlite3Fts3InitTokenizer(pHash, "simple", &pTokenizer, pzErr);
+    if( rc!=SQLITE_OK ) goto fts3_init_out;
+  }
+  assert( pTokenizer );
+
+
+  /* Allocate and populate the Fts3Table structure. */
+  nByte = sizeof(Fts3Table) +              /* Fts3Table */
+          nCol * sizeof(char *) +              /* azColumn */
+          nName +                              /* zName */
+          nDb +                                /* zDb */
+          nString;                             /* Space for azColumn strings */
+  p = (Fts3Table*)sqlite3_malloc(nByte);
+  if( p==0 ){
+    rc = SQLITE_NOMEM;
+    goto fts3_init_out;
+  }
+  memset(p, 0, nByte);
+  p->db = db;
+  p->nColumn = nCol;
+  p->nPendingData = 0;
+  p->azColumn = (char **)&p[1];
+  p->pTokenizer = pTokenizer;
+  p->nNodeSize = 1000;
+  p->nMaxPendingData = FTS3_MAX_PENDING_DATA;
+  p->bHasDocsize = (isFts4 && bNoDocsize==0);
+  p->bHasStat = isFts4;
+  fts3HashInit(&p->pendingTerms, FTS3_HASH_STRING, 1);
+
+  /* Fill in the zName and zDb fields of the vtab structure. */
+  zCsr = (char *)&p->azColumn[nCol];
+  p->zName = zCsr;
+  memcpy(zCsr, argv[2], nName);
+  zCsr += nName;
+  p->zDb = zCsr;
+  memcpy(zCsr, argv[1], nDb);
+  zCsr += nDb;
+
+  /* Fill in the azColumn array */
+  for(iCol=0; iCol<nCol; iCol++){
+    char *z; 
+    int n;
+    z = (char *)sqlite3Fts3NextToken(aCol[iCol], &n);
+    memcpy(zCsr, z, n);
+    zCsr[n] = '\0';
+    sqlite3Fts3Dequote(zCsr);
+    p->azColumn[iCol] = zCsr;
+    zCsr += n+1;
+    assert( zCsr <= &((char *)p)[nByte] );
+  }
+
+  if( (zCompress==0)!=(zUncompress==0) ){
+    char const *zMiss = (zCompress==0 ? "compress" : "uncompress");
+    rc = SQLITE_ERROR;
+    *pzErr = sqlite3_mprintf("missing %s parameter in fts4 constructor", zMiss);
+  }
+  p->zReadExprlist = fts3ReadExprList(p, zUncompress, &rc);
+  p->zWriteExprlist = fts3WriteExprList(p, zCompress, &rc);
+  if( rc!=SQLITE_OK ) goto fts3_init_out;
+
+  /* If this is an xCreate call, create the underlying tables in the 
+  ** database. TODO: For xConnect(), it could verify that said tables exist.
+  */
+  if( isCreate ){
+    rc = fts3CreateTables(p);
+  }
+
+  /* Figure out the page-size for the database. This is required in order to
+  ** estimate the cost of loading large doclists from the database (see 
+  ** function sqlite3Fts3SegReaderCost() for details).
+  */
+  fts3DatabasePageSize(&rc, p);
+
+  /* Declare the table schema to SQLite. */
+  fts3DeclareVtab(&rc, p);
+
+fts3_init_out:
+  sqlite3_free(zCompress);
+  sqlite3_free(zUncompress);
+  sqlite3_free((void *)aCol);
+  if( rc!=SQLITE_OK ){
+    if( p ){
+      fts3DisconnectMethod((sqlite3_vtab *)p);
+    }else if( pTokenizer ){
+      pTokenizer->pModule->xDestroy(pTokenizer);
+    }
+  }else{
+    *ppVTab = &p->base;
+  }
+  return rc;
+}
+
+/*
+** The xConnect() and xCreate() methods for the virtual table. All the
+** work is done in function fts3InitVtab().
+*/
+static int fts3ConnectMethod(
+  sqlite3 *db,                    /* Database connection */
+  void *pAux,                     /* Pointer to tokenizer hash table */
+  int argc,                       /* Number of elements in argv array */
+  const char * const *argv,       /* xCreate/xConnect argument array */
+  sqlite3_vtab **ppVtab,          /* OUT: New sqlite3_vtab object */
+  char **pzErr                    /* OUT: sqlite3_malloc'd error message */
+){
+  return fts3InitVtab(0, db, pAux, argc, argv, ppVtab, pzErr);
+}
+static int fts3CreateMethod(
+  sqlite3 *db,                    /* Database connection */
+  void *pAux,                     /* Pointer to tokenizer hash table */
+  int argc,                       /* Number of elements in argv array */
+  const char * const *argv,       /* xCreate/xConnect argument array */
+  sqlite3_vtab **ppVtab,          /* OUT: New sqlite3_vtab object */
+  char **pzErr                    /* OUT: sqlite3_malloc'd error message */
+){
+  return fts3InitVtab(1, db, pAux, argc, argv, ppVtab, pzErr);
+}
+
+/* 
+** Implementation of the xBestIndex method for FTS3 tables. There
+** are three possible strategies, in order of preference:
+**
+**   1. Direct lookup by rowid or docid. 
+**   2. Full-text search using a MATCH operator on a non-docid column.
+**   3. Linear scan of %_content table.
+*/
+static int fts3BestIndexMethod(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
+  Fts3Table *p = (Fts3Table *)pVTab;
+  int i;                          /* Iterator variable */
+  int iCons = -1;                 /* Index of constraint to use */
+
+  /* By default use a full table scan. This is an expensive option,
+  ** so search through the constraints to see if a more efficient 
+  ** strategy is possible.
+  */
+  pInfo->idxNum = FTS3_FULLSCAN_SEARCH;
+  pInfo->estimatedCost = 500000;
+  for(i=0; i<pInfo->nConstraint; i++){
+    struct sqlite3_index_constraint *pCons = &pInfo->aConstraint[i];
+    if( pCons->usable==0 ) continue;
+
+    /* A direct lookup on the rowid or docid column. Assign a cost of 1.0. */
+    if( pCons->op==SQLITE_INDEX_CONSTRAINT_EQ 
+     && (pCons->iColumn<0 || pCons->iColumn==p->nColumn+1 )
+    ){
+      pInfo->idxNum = FTS3_DOCID_SEARCH;
+      pInfo->estimatedCost = 1.0;
+      iCons = i;
+    }
+
+    /* A MATCH constraint. Use a full-text search.
+    **
+    ** If there is more than one MATCH constraint available, use the first
+    ** one encountered. If there is both a MATCH constraint and a direct
+    ** rowid/docid lookup, prefer the MATCH strategy. This is done even 
+    ** though the rowid/docid lookup is faster than a MATCH query, selecting
+    ** it would lead to an "unable to use function MATCH in the requested 
+    ** context" error.
+    */
+    if( pCons->op==SQLITE_INDEX_CONSTRAINT_MATCH 
+     && pCons->iColumn>=0 && pCons->iColumn<=p->nColumn
+    ){
+      pInfo->idxNum = FTS3_FULLTEXT_SEARCH + pCons->iColumn;
+      pInfo->estimatedCost = 2.0;
+      iCons = i;
+      break;
+    }
+  }
+
+  if( iCons>=0 ){
+    pInfo->aConstraintUsage[iCons].argvIndex = 1;
+    pInfo->aConstraintUsage[iCons].omit = 1;
+  } 
+  return SQLITE_OK;
+}
+
+/*
+** Implementation of xOpen method.
+*/
+static int fts3OpenMethod(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCsr){
+  sqlite3_vtab_cursor *pCsr;               /* Allocated cursor */
+
+  UNUSED_PARAMETER(pVTab);
+
+  /* Allocate a buffer large enough for an Fts3Cursor structure. If the
+  ** allocation succeeds, zero it and return SQLITE_OK. Otherwise, 
+  ** if the allocation fails, return SQLITE_NOMEM.
+  */
+  *ppCsr = pCsr = (sqlite3_vtab_cursor *)sqlite3_malloc(sizeof(Fts3Cursor));
+  if( !pCsr ){
+    return SQLITE_NOMEM;
+  }
+  memset(pCsr, 0, sizeof(Fts3Cursor));
+  return SQLITE_OK;
+}
+
+/*
+** Close the cursor.  For additional information see the documentation
+** on the xClose method of the virtual table interface.
+*/
+static int fts3CloseMethod(sqlite3_vtab_cursor *pCursor){
+  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
+  assert( ((Fts3Table *)pCsr->base.pVtab)->pSegments==0 );
+  sqlite3_finalize(pCsr->pStmt);
+  sqlite3Fts3ExprFree(pCsr->pExpr);
+  sqlite3Fts3FreeDeferredTokens(pCsr);
+  sqlite3_free(pCsr->aDoclist);
+  sqlite3_free(pCsr->aMatchinfo);
+  sqlite3_free(pCsr);
+  return SQLITE_OK;
+}
+
+/*
+** Position the pCsr->pStmt statement so that it is on the row
+** of the %_content table that contains the last match.  Return
+** SQLITE_OK on success.  
+*/
+static int fts3CursorSeek(sqlite3_context *pContext, Fts3Cursor *pCsr){
+  if( pCsr->isRequireSeek ){
+    pCsr->isRequireSeek = 0;
+    sqlite3_bind_int64(pCsr->pStmt, 1, pCsr->iPrevId);
+    if( SQLITE_ROW==sqlite3_step(pCsr->pStmt) ){
+      return SQLITE_OK;
+    }else{
+      int rc = sqlite3_reset(pCsr->pStmt);
+      if( rc==SQLITE_OK ){
+        /* If no row was found and no error has occured, then the %_content
+        ** table is missing a row that is present in the full-text index.
+        ** The data structures are corrupt.
+        */
+        rc = SQLITE_CORRUPT;
+      }
+      pCsr->isEof = 1;
+      if( pContext ){
+        sqlite3_result_error_code(pContext, rc);
+      }
+      return rc;
+    }
+  }else{
+    return SQLITE_OK;
+  }
+}
+
+/*
+** This function is used to process a single interior node when searching
+** a b-tree for a term or term prefix. The node data is passed to this 
+** function via the zNode/nNode parameters. The term to search for is
+** passed in zTerm/nTerm.
+**
+** If piFirst is not NULL, then this function sets *piFirst to the blockid
+** of the child node that heads the sub-tree that may contain the term.
+**
+** If piLast is not NULL, then *piLast is set to the right-most child node
+** that heads a sub-tree that may contain a term for which zTerm/nTerm is
+** a prefix.
+**
+** If an OOM error occurs, SQLITE_NOMEM is returned. Otherwise, SQLITE_OK.
+*/
+static int fts3ScanInteriorNode(
+  const char *zTerm,              /* Term to select leaves for */
+  int nTerm,                      /* Size of term zTerm in bytes */
+  const char *zNode,              /* Buffer containing segment interior node */
+  int nNode,                      /* Size of buffer at zNode */
+  sqlite3_int64 *piFirst,         /* OUT: Selected child node */
+  sqlite3_int64 *piLast           /* OUT: Selected child node */
+){
+  int rc = SQLITE_OK;             /* Return code */
+  const char *zCsr = zNode;       /* Cursor to iterate through node */
+  const char *zEnd = &zCsr[nNode];/* End of interior node buffer */
+  char *zBuffer = 0;              /* Buffer to load terms into */
+  int nAlloc = 0;                 /* Size of allocated buffer */
+  int isFirstTerm = 1;            /* True when processing first term on page */
+  sqlite3_int64 iChild;           /* Block id of child node to descend to */
+
+  /* Skip over the 'height' varint that occurs at the start of every 
+  ** interior node. Then load the blockid of the left-child of the b-tree
+  ** node into variable iChild.  
+  **
+  ** Even if the data structure on disk is corrupted, this (reading two
+  ** varints from the buffer) does not risk an overread. If zNode is a
+  ** root node, then the buffer comes from a SELECT statement. SQLite does
+  ** not make this guarantee explicitly, but in practice there are always
+  ** either more than 20 bytes of allocated space following the nNode bytes of
+  ** contents, or two zero bytes. Or, if the node is read from the %_segments
+  ** table, then there are always 20 bytes of zeroed padding following the
+  ** nNode bytes of content (see sqlite3Fts3ReadBlock() for details).
+  */
+  zCsr += sqlite3Fts3GetVarint(zCsr, &iChild);
+  zCsr += sqlite3Fts3GetVarint(zCsr, &iChild);
+  if( zCsr>zEnd ){
+    return SQLITE_CORRUPT;
+  }
+  
+  while( zCsr<zEnd && (piFirst || piLast) ){
+    int cmp;                      /* memcmp() result */
+    int nSuffix;                  /* Size of term suffix */
+    int nPrefix = 0;              /* Size of term prefix */
+    int nBuffer;                  /* Total term size */
+  
+    /* Load the next term on the node into zBuffer. Use realloc() to expand
+    ** the size of zBuffer if required.  */
+    if( !isFirstTerm ){
+      zCsr += sqlite3Fts3GetVarint32(zCsr, &nPrefix);
+    }
+    isFirstTerm = 0;
+    zCsr += sqlite3Fts3GetVarint32(zCsr, &nSuffix);
+    
+    /* NOTE(shess): Previous code checked for negative nPrefix and
+    ** nSuffix and suffix overrunning zEnd.  Additionally corrupt if
+    ** the prefix is longer than the previous term, or if the suffix
+    ** causes overflow.
+    */
+    if( nPrefix<0 || nSuffix<0 || nPrefix>nBuffer
+     || &zCsr[nSuffix]<zCsr || &zCsr[nSuffix]>zEnd ){
+      rc = SQLITE_CORRUPT;
+      goto finish_scan;
+    }
+    if( nPrefix+nSuffix>nAlloc ){
+      char *zNew;
+      nAlloc = (nPrefix+nSuffix) * 2;
+      zNew = (char *)sqlite3_realloc(zBuffer, nAlloc);
+      if( !zNew ){
+        rc = SQLITE_NOMEM;
+        goto finish_scan;
+      }
+      zBuffer = zNew;
+    }
+    memcpy(&zBuffer[nPrefix], zCsr, nSuffix);
+    nBuffer = nPrefix + nSuffix;
+    zCsr += nSuffix;
+
+    /* Compare the term we are searching for with the term just loaded from
+    ** the interior node. If the specified term is greater than or equal
+    ** to the term from the interior node, then all terms on the sub-tree 
+    ** headed by node iChild are smaller than zTerm. No need to search 
+    ** iChild.
+    **
+    ** If the interior node term is larger than the specified term, then
+    ** the tree headed by iChild may contain the specified term.
+    */
+    cmp = memcmp(zTerm, zBuffer, (nBuffer>nTerm ? nTerm : nBuffer));
+    if( piFirst && (cmp<0 || (cmp==0 && nBuffer>nTerm)) ){
+      *piFirst = iChild;
+      piFirst = 0;
+    }
+
+    if( piLast && cmp<0 ){
+      *piLast = iChild;
+      piLast = 0;
+    }
+
+    iChild++;
+  };
+
+  if( piFirst ) *piFirst = iChild;
+  if( piLast ) *piLast = iChild;
+
+ finish_scan:
+  sqlite3_free(zBuffer);
+  return rc;
+}
+
+
+/*
+** The buffer pointed to by argument zNode (size nNode bytes) contains an
+** interior node of a b-tree segment. The zTerm buffer (size nTerm bytes)
+** contains a term. This function searches the sub-tree headed by the zNode
+** node for the range of leaf nodes that may contain the specified term
+** or terms for which the specified term is a prefix.
+**
+** If piLeaf is not NULL, then *piLeaf is set to the blockid of the 
+** left-most leaf node in the tree that may contain the specified term.
+** If piLeaf2 is not NULL, then *piLeaf2 is set to the blockid of the
+** right-most leaf node that may contain a term for which the specified
+** term is a prefix.
+**
+** It is possible that the range of returned leaf nodes does not contain 
+** the specified term or any terms for which it is a prefix. However, if the 
+** segment does contain any such terms, they are stored within the identified
+** range. Because this function only inspects interior segment nodes (and
+** never loads leaf nodes into memory), it is not possible to be sure.
+**
+** If an error occurs, an error code other than SQLITE_OK is returned.
+*/ 
+static int fts3SelectLeaf(
+  Fts3Table *p,                   /* Virtual table handle */
+  const char *zTerm,              /* Term to select leaves for */
+  int nTerm,                      /* Size of term zTerm in bytes */
+  const char *zNode,              /* Buffer containing segment interior node */
+  int nNode,                      /* Size of buffer at zNode */
+  sqlite3_int64 *piLeaf,          /* Selected leaf node */
+  sqlite3_int64 *piLeaf2          /* Selected leaf node */
+){
+  int rc;                         /* Return code */
+  int iHeight;                    /* Height of this node in tree */
+
+  assert( piLeaf || piLeaf2 );
+
+  sqlite3Fts3GetVarint32(zNode, &iHeight);
+  rc = fts3ScanInteriorNode(zTerm, nTerm, zNode, nNode, piLeaf, piLeaf2);
+  assert( !piLeaf2 || !piLeaf || rc!=SQLITE_OK || (*piLeaf<=*piLeaf2) );
+
+  if( rc==SQLITE_OK && iHeight>1 ){
+    char *zBlob = 0;              /* Blob read from %_segments table */
+    int nBlob;                    /* Size of zBlob in bytes */
+
+    if( piLeaf && piLeaf2 && (*piLeaf!=*piLeaf2) ){
+      rc = sqlite3Fts3ReadBlock(p, *piLeaf, &zBlob, &nBlob);
+      if( rc==SQLITE_OK ){
+        rc = fts3SelectLeaf(p, zTerm, nTerm, zBlob, nBlob, piLeaf, 0);
+      }
+      sqlite3_free(zBlob);
+      piLeaf = 0;
+      zBlob = 0;
+    }
+
+    if( rc==SQLITE_OK ){
+      rc = sqlite3Fts3ReadBlock(p, piLeaf ? *piLeaf : *piLeaf2, &zBlob, &nBlob);
+    }
+    if( rc==SQLITE_OK ){
+      rc = fts3SelectLeaf(p, zTerm, nTerm, zBlob, nBlob, piLeaf, piLeaf2);
+    }
+    sqlite3_free(zBlob);
+  }
+
+  return rc;
+}
+
+/*
+** This function is used to create delta-encoded serialized lists of FTS3 
+** varints. Each call to this function appends a single varint to a list.
+*/
+static void fts3PutDeltaVarint(
+  char **pp,                      /* IN/OUT: Output pointer */
+  sqlite3_int64 *piPrev,          /* IN/OUT: Previous value written to list */
+  sqlite3_int64 iVal              /* Write this value to the list */
+){
+  assert( iVal-*piPrev > 0 || (*piPrev==0 && iVal==0) );
+  *pp += sqlite3Fts3PutVarint(*pp, iVal-*piPrev);
+  *piPrev = iVal;
+}
+
+/*
+** When this function is called, *ppPoslist is assumed to point to the 
+** start of a position-list. After it returns, *ppPoslist points to the
+** first byte after the position-list.
+**
+** A position list is list of positions (delta encoded) and columns for 
+** a single document record of a doclist.  So, in other words, this
+** routine advances *ppPoslist so that it points to the next docid in
+** the doclist, or to the first byte past the end of the doclist.
+**
+** If pp is not NULL, then the contents of the position list are copied
+** to *pp. *pp is set to point to the first byte past the last byte copied
+** before this function returns.
+*/
+static void fts3PoslistCopy(char **pp, char **ppPoslist){
+  char *pEnd = *ppPoslist;
+  char c = 0;
+
+  /* The end of a position list is marked by a zero encoded as an FTS3 
+  ** varint. A single POS_END (0) byte. Except, if the 0 byte is preceded by
+  ** a byte with the 0x80 bit set, then it is not a varint 0, but the tail
+  ** of some other, multi-byte, value.
+  **
+  ** The following while-loop moves pEnd to point to the first byte that is not 
+  ** immediately preceded by a byte with the 0x80 bit set. Then increments
+  ** pEnd once more so that it points to the byte immediately following the
+  ** last byte in the position-list.
+  */
+  while( *pEnd | c ){
+    c = *pEnd++ & 0x80;
+    testcase( c!=0 && (*pEnd)==0 );
+  }
+  pEnd++;  /* Advance past the POS_END terminator byte */
+
+  if( pp ){
+    int n = (int)(pEnd - *ppPoslist);
+    char *p = *pp;
+    memcpy(p, *ppPoslist, n);
+    p += n;
+    *pp = p;
+  }
+  *ppPoslist = pEnd;
+}
+
+/*
+** When this function is called, *ppPoslist is assumed to point to the 
+** start of a column-list. After it returns, *ppPoslist points to the
+** to the terminator (POS_COLUMN or POS_END) byte of the column-list.
+**
+** A column-list is list of delta-encoded positions for a single column
+** within a single document within a doclist.
+**
+** The column-list is terminated either by a POS_COLUMN varint (1) or
+** a POS_END varint (0).  This routine leaves *ppPoslist pointing to
+** the POS_COLUMN or POS_END that terminates the column-list.
+**
+** If pp is not NULL, then the contents of the column-list are copied
+** to *pp. *pp is set to point to the first byte past the last byte copied
+** before this function returns.  The POS_COLUMN or POS_END terminator
+** is not copied into *pp.
+*/
+static void fts3ColumnlistCopy(char **pp, char **ppPoslist){
+  char *pEnd = *ppPoslist;
+  char c = 0;
+
+  /* A column-list is terminated by either a 0x01 or 0x00 byte that is
+  ** not part of a multi-byte varint.
+  */
+  while( 0xFE & (*pEnd | c) ){
+    c = *pEnd++ & 0x80;
+    testcase( c!=0 && ((*pEnd)&0xfe)==0 );
+  }
+  if( pp ){
+    int n = (int)(pEnd - *ppPoslist);
+    char *p = *pp;
+    memcpy(p, *ppPoslist, n);
+    p += n;
+    *pp = p;
+  }
+  *ppPoslist = pEnd;
+}
+
+/*
+** Value used to signify the end of an position-list. This is safe because
+** it is not possible to have a document with 2^31 terms.
+*/
+#define POSITION_LIST_END 0x7fffffff
+
+/*
+** This function is used to help parse position-lists. When this function is
+** called, *pp may point to the start of the next varint in the position-list
+** being parsed, or it may point to 1 byte past the end of the position-list
+** (in which case **pp will be a terminator bytes POS_END (0) or
+** (1)).
+**
+** If *pp points past the end of the current position-list, set *pi to 
+** POSITION_LIST_END and return. Otherwise, read the next varint from *pp,
+** increment the current value of *pi by the value read, and set *pp to
+** point to the next value before returning.
+**
+** Before calling this routine *pi must be initialized to the value of
+** the previous position, or zero if we are reading the first position
+** in the position-list.  Because positions are delta-encoded, the value
+** of the previous position is needed in order to compute the value of
+** the next position.
+*/
+static void fts3ReadNextPos(
+  char **pp,                    /* IN/OUT: Pointer into position-list buffer */
+  sqlite3_int64 *pi             /* IN/OUT: Value read from position-list */
+){
+  if( (**pp)&0xFE ){
+    fts3GetDeltaVarint(pp, pi);
+    *pi -= 2;
+  }else{
+    *pi = POSITION_LIST_END;
+  }
+}
+
+/*
+** If parameter iCol is not 0, write an POS_COLUMN (1) byte followed by
+** the value of iCol encoded as a varint to *pp.   This will start a new
+** column list.
+**
+** Set *pp to point to the byte just after the last byte written before 
+** returning (do not modify it if iCol==0). Return the total number of bytes
+** written (0 if iCol==0).
+*/
+static int fts3PutColNumber(char **pp, int iCol){
+  int n = 0;                      /* Number of bytes written */
+  if( iCol ){
+    char *p = *pp;                /* Output pointer */
+    n = 1 + sqlite3Fts3PutVarint(&p[1], iCol);
+    *p = 0x01;
+    *pp = &p[n];
+  }
+  return n;
+}
+
+/*
+** Compute the union of two position lists.  The output written
+** into *pp contains all positions of both *pp1 and *pp2 in sorted
+** order and with any duplicates removed.  All pointers are
+** updated appropriately.   The caller is responsible for insuring
+** that there is enough space in *pp to hold the complete output.
+*/
+static void fts3PoslistMerge(
+  char **pp,                      /* Output buffer */
+  char **pp1,                     /* Left input list */
+  char **pp2                      /* Right input list */
+){
+  char *p = *pp;
+  char *p1 = *pp1;
+  char *p2 = *pp2;
+
+  while( *p1 || *p2 ){
+    int iCol1;         /* The current column index in pp1 */
+    int iCol2;         /* The current column index in pp2 */
+
+    if( *p1==POS_COLUMN ) sqlite3Fts3GetVarint32(&p1[1], &iCol1);
+    else if( *p1==POS_END ) iCol1 = POSITION_LIST_END;
+    else iCol1 = 0;
+
+    if( *p2==POS_COLUMN ) sqlite3Fts3GetVarint32(&p2[1], &iCol2);
+    else if( *p2==POS_END ) iCol2 = POSITION_LIST_END;
+    else iCol2 = 0;
+
+    if( iCol1==iCol2 ){
+      sqlite3_int64 i1 = 0;       /* Last position from pp1 */
+      sqlite3_int64 i2 = 0;       /* Last position from pp2 */
+      sqlite3_int64 iPrev = 0;
+      int n = fts3PutColNumber(&p, iCol1);
+      p1 += n;
+      p2 += n;
+
+      /* At this point, both p1 and p2 point to the start of column-lists
+      ** for the same column (the column with index iCol1 and iCol2).
+      ** A column-list is a list of non-negative delta-encoded varints, each 
+      ** incremented by 2 before being stored. Each list is terminated by a
+      ** POS_END (0) or POS_COLUMN (1). The following block merges the two lists
+      ** and writes the results to buffer p. p is left pointing to the byte
+      ** after the list written. No terminator (POS_END or POS_COLUMN) is
+      ** written to the output.
+      */
+      fts3GetDeltaVarint(&p1, &i1);
+      fts3GetDeltaVarint(&p2, &i2);
+      do {
+        fts3PutDeltaVarint(&p, &iPrev, (i1<i2) ? i1 : i2); 
+        iPrev -= 2;
+        if( i1==i2 ){
+          fts3ReadNextPos(&p1, &i1);
+          fts3ReadNextPos(&p2, &i2);
+        }else if( i1<i2 ){
+          fts3ReadNextPos(&p1, &i1);
+        }else{
+          fts3ReadNextPos(&p2, &i2);
+        }
+      }while( i1!=POSITION_LIST_END || i2!=POSITION_LIST_END );
+    }else if( iCol1<iCol2 ){
+      p1 += fts3PutColNumber(&p, iCol1);
+      fts3ColumnlistCopy(&p, &p1);
+    }else{
+      p2 += fts3PutColNumber(&p, iCol2);
+      fts3ColumnlistCopy(&p, &p2);
+    }
+  }
+
+  *p++ = POS_END;
+  *pp = p;
+  *pp1 = p1 + 1;
+  *pp2 = p2 + 1;
+}
+
+/*
+** nToken==1 searches for adjacent positions.
+**
+** This function is used to merge two position lists into one. When it is
+** called, *pp1 and *pp2 must both point to position lists. A position-list is
+** the part of a doclist that follows each document id. For example, if a row
+** contains:
+**
+**     'a b c'|'x y z'|'a b b a'
+**
+** Then the position list for this row for token 'b' would consist of:
+**
+**     0x02 0x01 0x02 0x03 0x03 0x00
+**
+** When this function returns, both *pp1 and *pp2 are left pointing to the
+** byte following the 0x00 terminator of their respective position lists.
+**
+** If isSaveLeft is 0, an entry is added to the output position list for 
+** each position in *pp2 for which there exists one or more positions in
+** *pp1 so that (pos(*pp2)>pos(*pp1) && pos(*pp2)-pos(*pp1)<=nToken). i.e.
+** when the *pp1 token appears before the *pp2 token, but not more than nToken
+** slots before it.
+*/
+static int fts3PoslistPhraseMerge(
+  char **pp,                      /* IN/OUT: Preallocated output buffer */
+  int nToken,                     /* Maximum difference in token positions */
+  int isSaveLeft,                 /* Save the left position */
+  int isExact,                    /* If *pp1 is exactly nTokens before *pp2 */
+  char **pp1,                     /* IN/OUT: Left input list */
+  char **pp2                      /* IN/OUT: Right input list */
+){
+  char *p = (pp ? *pp : 0);
+  char *p1 = *pp1;
+  char *p2 = *pp2;
+  int iCol1 = 0;
+  int iCol2 = 0;
+
+  /* Never set both isSaveLeft and isExact for the same invocation. */
+  assert( isSaveLeft==0 || isExact==0 );
+
+  assert( *p1!=0 && *p2!=0 );
+  if( *p1==POS_COLUMN ){ 
+    p1++;
+    p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
+  }
+  if( *p2==POS_COLUMN ){ 
+    p2++;
+    p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
+  }
+
+  while( 1 ){
+    if( iCol1==iCol2 ){
+      char *pSave = p;
+      sqlite3_int64 iPrev = 0;
+      sqlite3_int64 iPos1 = 0;
+      sqlite3_int64 iPos2 = 0;
+
+      if( pp && iCol1 ){
+        *p++ = POS_COLUMN;
+        p += sqlite3Fts3PutVarint(p, iCol1);
+      }
+
+      assert( *p1!=POS_END && *p1!=POS_COLUMN );
+      assert( *p2!=POS_END && *p2!=POS_COLUMN );
+      fts3GetDeltaVarint(&p1, &iPos1); iPos1 -= 2;
+      fts3GetDeltaVarint(&p2, &iPos2); iPos2 -= 2;
+
+      while( 1 ){
+        if( iPos2==iPos1+nToken 
+         || (isExact==0 && iPos2>iPos1 && iPos2<=iPos1+nToken) 
+        ){
+          sqlite3_int64 iSave;
+          if( !pp ){
+            fts3PoslistCopy(0, &p2);
+            fts3PoslistCopy(0, &p1);
+            *pp1 = p1;
+            *pp2 = p2;
+            return 1;
+          }
+          iSave = isSaveLeft ? iPos1 : iPos2;
+          fts3PutDeltaVarint(&p, &iPrev, iSave+2); iPrev -= 2;
+          pSave = 0;
+        }
+        if( (!isSaveLeft && iPos2<=(iPos1+nToken)) || iPos2<=iPos1 ){
+          if( (*p2&0xFE)==0 ) break;
+          fts3GetDeltaVarint(&p2, &iPos2); iPos2 -= 2;
+        }else{
+          if( (*p1&0xFE)==0 ) break;
+          fts3GetDeltaVarint(&p1, &iPos1); iPos1 -= 2;
+        }
+      }
+
+      if( pSave ){
+        assert( pp && p );
+        p = pSave;
+      }
+
+      fts3ColumnlistCopy(0, &p1);
+      fts3ColumnlistCopy(0, &p2);
+      assert( (*p1&0xFE)==0 && (*p2&0xFE)==0 );
+      if( 0==*p1 || 0==*p2 ) break;
+
+      p1++;
+      p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
+      p2++;
+      p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
+    }
+
+    /* Advance pointer p1 or p2 (whichever corresponds to the smaller of
+    ** iCol1 and iCol2) so that it points to either the 0x00 that marks the
+    ** end of the position list, or the 0x01 that precedes the next 
+    ** column-number in the position list. 
+    */
+    else if( iCol1<iCol2 ){
+      fts3ColumnlistCopy(0, &p1);
+      if( 0==*p1 ) break;
+      p1++;
+      p1 += sqlite3Fts3GetVarint32(p1, &iCol1);
+    }else{
+      fts3ColumnlistCopy(0, &p2);
+      if( 0==*p2 ) break;
+      p2++;
+      p2 += sqlite3Fts3GetVarint32(p2, &iCol2);
+    }
+  }
+
+  fts3PoslistCopy(0, &p2);
+  fts3PoslistCopy(0, &p1);
+  *pp1 = p1;
+  *pp2 = p2;
+  if( !pp || *pp==p ){
+    return 0;
+  }
+  *p++ = 0x00;
+  *pp = p;
+  return 1;
+}
+
+/*
+** Merge two position-lists as required by the NEAR operator.
+*/
+static int fts3PoslistNearMerge(
+  char **pp,                      /* Output buffer */
+  char *aTmp,                     /* Temporary buffer space */
+  int nRight,                     /* Maximum difference in token positions */
+  int nLeft,                      /* Maximum difference in token positions */
+  char **pp1,                     /* IN/OUT: Left input list */
+  char **pp2                      /* IN/OUT: Right input list */
+){
+  char *p1 = *pp1;
+  char *p2 = *pp2;
+
+  if( !pp ){
+    if( fts3PoslistPhraseMerge(0, nRight, 0, 0, pp1, pp2) ) return 1;
+    *pp1 = p1;
+    *pp2 = p2;
+    return fts3PoslistPhraseMerge(0, nLeft, 0, 0, pp2, pp1);
+  }else{
+    char *pTmp1 = aTmp;
+    char *pTmp2;
+    char *aTmp2;
+    int res = 1;
+
+    fts3PoslistPhraseMerge(&pTmp1, nRight, 0, 0, pp1, pp2);
+    aTmp2 = pTmp2 = pTmp1;
+    *pp1 = p1;
+    *pp2 = p2;
+    fts3PoslistPhraseMerge(&pTmp2, nLeft, 1, 0, pp2, pp1);
+    if( pTmp1!=aTmp && pTmp2!=aTmp2 ){
+      fts3PoslistMerge(pp, &aTmp, &aTmp2);
+    }else if( pTmp1!=aTmp ){
+      fts3PoslistCopy(pp, &aTmp);
+    }else if( pTmp2!=aTmp2 ){
+      fts3PoslistCopy(pp, &aTmp2);
+    }else{
+      res = 0;
+    }
+
+    return res;
+  }
+}
+
+/*
+** Values that may be used as the first parameter to fts3DoclistMerge().
+*/
+#define MERGE_NOT        2        /* D + D -> D */
+#define MERGE_AND        3        /* D + D -> D */
+#define MERGE_OR         4        /* D + D -> D */
+#define MERGE_POS_OR     5        /* P + P -> P */
+#define MERGE_PHRASE     6        /* P + P -> D */
+#define MERGE_POS_PHRASE 7        /* P + P -> P */
+#define MERGE_NEAR       8        /* P + P -> D */
+#define MERGE_POS_NEAR   9        /* P + P -> P */
+
+/*
+** Merge the two doclists passed in buffer a1 (size n1 bytes) and a2
+** (size n2 bytes). The output is written to pre-allocated buffer aBuffer,
+** which is guaranteed to be large enough to hold the results. The number
+** of bytes written to aBuffer is stored in *pnBuffer before returning.
+**
+** If successful, SQLITE_OK is returned. Otherwise, if a malloc error
+** occurs while allocating a temporary buffer as part of the merge operation,
+** SQLITE_NOMEM is returned.
+*/
+static int fts3DoclistMerge(
+  int mergetype,                  /* One of the MERGE_XXX constants */
+  int nParam1,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
+  int nParam2,                    /* Used by MERGE_NEAR and MERGE_POS_NEAR */
+  char *aBuffer,                  /* Pre-allocated output buffer */
+  int *pnBuffer,                  /* OUT: Bytes written to aBuffer */
+  char *a1,                       /* Buffer containing first doclist */
+  int n1,                         /* Size of buffer a1 */
+  char *a2,                       /* Buffer containing second doclist */
+  int n2,                         /* Size of buffer a2 */
+  int *pnDoc                      /* OUT: Number of docids in output */
+){
+  sqlite3_int64 i1 = 0;
+  sqlite3_int64 i2 = 0;
+  sqlite3_int64 iPrev = 0;
+
+  char *p = aBuffer;
+  char *p1 = a1;
+  char *p2 = a2;
+  char *pEnd1 = &a1[n1];
+  char *pEnd2 = &a2[n2];
+  int nDoc = 0;
+
+  assert( mergetype==MERGE_OR     || mergetype==MERGE_POS_OR 
+       || mergetype==MERGE_AND    || mergetype==MERGE_NOT
+       || mergetype==MERGE_PHRASE || mergetype==MERGE_POS_PHRASE
+       || mergetype==MERGE_NEAR   || mergetype==MERGE_POS_NEAR
+  );
+
+  if( !aBuffer ){
+    *pnBuffer = 0;
+    return SQLITE_NOMEM;
+  }
+
+  /* Read the first docid from each doclist */
+  fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+  fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+
+  switch( mergetype ){
+    case MERGE_OR:
+    case MERGE_POS_OR:
+      while( p1 || p2 ){
+        if( p2 && p1 && i1==i2 ){
+          fts3PutDeltaVarint(&p, &iPrev, i1);
+          if( mergetype==MERGE_POS_OR ) fts3PoslistMerge(&p, &p1, &p2);
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }else if( !p2 || (p1 && i1<i2) ){
+          fts3PutDeltaVarint(&p, &iPrev, i1);
+          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p1);
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+        }else{
+          fts3PutDeltaVarint(&p, &iPrev, i2);
+          if( mergetype==MERGE_POS_OR ) fts3PoslistCopy(&p, &p2);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }
+      }
+      break;
+
+    case MERGE_AND:
+      while( p1 && p2 ){
+        if( i1==i2 ){
+          fts3PutDeltaVarint(&p, &iPrev, i1);
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+          nDoc++;
+        }else if( i1<i2 ){
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+        }else{
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }
+      }
+      break;
+
+    case MERGE_NOT:
+      while( p1 ){
+        if( p2 && i1==i2 ){
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }else if( !p2 || i1<i2 ){
+          fts3PutDeltaVarint(&p, &iPrev, i1);
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+        }else{
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }
+      }
+      break;
+
+    case MERGE_POS_PHRASE:
+    case MERGE_PHRASE: {
+      char **ppPos = (mergetype==MERGE_PHRASE ? 0 : &p);
+      while( p1 && p2 ){
+        if( i1==i2 ){
+          char *pSave = p;
+          sqlite3_int64 iPrevSave = iPrev;
+          fts3PutDeltaVarint(&p, &iPrev, i1);
+          if( 0==fts3PoslistPhraseMerge(ppPos, nParam1, 0, 1, &p1, &p2) ){
+            p = pSave;
+            iPrev = iPrevSave;
+          }else{
+            nDoc++;
+          }
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }else if( i1<i2 ){
+          fts3PoslistCopy(0, &p1);
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+        }else{
+          fts3PoslistCopy(0, &p2);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }
+      }
+      break;
+    }
+
+    default: assert( mergetype==MERGE_POS_NEAR || mergetype==MERGE_NEAR ); {
+      char *aTmp = 0;
+      char **ppPos = 0;
+
+      if( mergetype==MERGE_POS_NEAR ){
+        ppPos = &p;
+        aTmp = sqlite3_malloc(2*(n1+n2+1));
+        if( !aTmp ){
+          return SQLITE_NOMEM;
+        }
+      }
+
+      while( p1 && p2 ){
+        if( i1==i2 ){
+          char *pSave = p;
+          sqlite3_int64 iPrevSave = iPrev;
+          fts3PutDeltaVarint(&p, &iPrev, i1);
+
+          if( !fts3PoslistNearMerge(ppPos, aTmp, nParam1, nParam2, &p1, &p2) ){
+            iPrev = iPrevSave;
+            p = pSave;
+          }
+
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }else if( i1<i2 ){
+          fts3PoslistCopy(0, &p1);
+          fts3GetDeltaVarint2(&p1, pEnd1, &i1);
+        }else{
+          fts3PoslistCopy(0, &p2);
+          fts3GetDeltaVarint2(&p2, pEnd2, &i2);
+        }
+      }
+      sqlite3_free(aTmp);
+      break;
+    }
+  }
+
+  if( pnDoc ) *pnDoc = nDoc;
+  *pnBuffer = (int)(p-aBuffer);
+  return SQLITE_OK;
+}
+
+/* 
+** A pointer to an instance of this structure is used as the context 
+** argument to sqlite3Fts3SegReaderIterate()
+*/
+typedef struct TermSelect TermSelect;
+struct TermSelect {
+  int isReqPos;
+  char *aaOutput[16];             /* Malloc'd output buffer */
+  int anOutput[16];               /* Size of output in bytes */
+};
+
+/*
+** Merge all doclists in the TermSelect.aaOutput[] array into a single
+** doclist stored in TermSelect.aaOutput[0]. If successful, delete all
+** other doclists (except the aaOutput[0] one) and return SQLITE_OK.
+**
+** If an OOM error occurs, return SQLITE_NOMEM. In this case it is
+** the responsibility of the caller to free any doclists left in the
+** TermSelect.aaOutput[] array.
+*/
+static int fts3TermSelectMerge(TermSelect *pTS){
+  int mergetype = (pTS->isReqPos ? MERGE_POS_OR : MERGE_OR);
+  char *aOut = 0;
+  int nOut = 0;
+  int i;
+
+  /* Loop through the doclists in the aaOutput[] array. Merge them all
+  ** into a single doclist.
+  */
+  for(i=0; i<SizeofArray(pTS->aaOutput); i++){
+    if( pTS->aaOutput[i] ){
+      if( !aOut ){
+        aOut = pTS->aaOutput[i];
+        nOut = pTS->anOutput[i];
+        pTS->aaOutput[i] = 0;
+      }else{
+        int nNew = nOut + pTS->anOutput[i];
+        char *aNew = sqlite3_malloc(nNew);
+        if( !aNew ){
+          sqlite3_free(aOut);
+          return SQLITE_NOMEM;
+        }
+        fts3DoclistMerge(mergetype, 0, 0,
+            aNew, &nNew, pTS->aaOutput[i], pTS->anOutput[i], aOut, nOut, 0
+        );
+        sqlite3_free(pTS->aaOutput[i]);
+        sqlite3_free(aOut);
+        pTS->aaOutput[i] = 0;
+        aOut = aNew;
+        nOut = nNew;
+      }
+    }
+  }
+
+  pTS->aaOutput[0] = aOut;
+  pTS->anOutput[0] = nOut;
+  return SQLITE_OK;
+}
+
+/*
+** This function is used as the sqlite3Fts3SegReaderIterate() callback when
+** querying the full-text index for a doclist associated with a term or
+** term-prefix.
+*/
+static int fts3TermSelectCb(
+  Fts3Table *p,                   /* Virtual table object */
+  void *pContext,                 /* Pointer to TermSelect structure */
+  char *zTerm,
+  int nTerm,
+  char *aDoclist,
+  int nDoclist
+){
+  TermSelect *pTS = (TermSelect *)pContext;
+
+  UNUSED_PARAMETER(p);
+  UNUSED_PARAMETER(zTerm);
+  UNUSED_PARAMETER(nTerm);
+
+  if( pTS->aaOutput[0]==0 ){
+    /* If this is the first term selected, copy the doclist to the output
+    ** buffer using memcpy(). TODO: Add a way to transfer control of the
+    ** aDoclist buffer from the caller so as to avoid the memcpy().
+    */
+    pTS->aaOutput[0] = sqlite3_malloc(nDoclist);
+    pTS->anOutput[0] = nDoclist;
+    if( pTS->aaOutput[0] ){
+      memcpy(pTS->aaOutput[0], aDoclist, nDoclist);
+    }else{
+      return SQLITE_NOMEM;
+    }
+  }else{
+    int mergetype = (pTS->isReqPos ? MERGE_POS_OR : MERGE_OR);
+    char *aMerge = aDoclist;
+    int nMerge = nDoclist;
+    int iOut;
+
+    for(iOut=0; iOut<SizeofArray(pTS->aaOutput); iOut++){
+      char *aNew;
+      int nNew;
+      if( pTS->aaOutput[iOut]==0 ){
+        assert( iOut>0 );
+        pTS->aaOutput[iOut] = aMerge;
+        pTS->anOutput[iOut] = nMerge;
         break;
       }
+
+      nNew = nMerge + pTS->anOutput[iOut];
+      aNew = sqlite3_malloc(nNew);
+      if( !aNew ){
+        if( aMerge!=aDoclist ){
+          sqlite3_free(aMerge);
+        }
+        return SQLITE_NOMEM;
+      }
+      fts3DoclistMerge(mergetype, 0, 0, aNew, &nNew, 
+          pTS->aaOutput[iOut], pTS->anOutput[iOut], aMerge, nMerge, 0
+      );
+
+      if( iOut>0 ) sqlite3_free(aMerge);
+      sqlite3_free(pTS->aaOutput[iOut]);
+      pTS->aaOutput[iOut] = 0;
+
+      aMerge = aNew;
+      nMerge = nNew;
+      if( (iOut+1)==SizeofArray(pTS->aaOutput) ){
+        pTS->aaOutput[iOut] = aMerge;
+        pTS->anOutput[iOut] = nMerge;
+      }
+    }
+  }
+  return SQLITE_OK;
+}
+
+static int fts3DeferredTermSelect(
+  Fts3DeferredToken *pToken,      /* Phrase token */
+  int isTermPos,                  /* True to include positions */
+  int *pnOut,                     /* OUT: Size of list */
+  char **ppOut                    /* OUT: Body of list */
+){
+  char *aSource;
+  int nSource;
+
+  aSource = sqlite3Fts3DeferredDoclist(pToken, &nSource);
+  if( !aSource ){
+    *pnOut = 0;
+    *ppOut = 0;
+  }else if( isTermPos ){
+    *ppOut = sqlite3_malloc(nSource);
+    if( !*ppOut ) return SQLITE_NOMEM;
+    memcpy(*ppOut, aSource, nSource);
+    *pnOut = nSource;
+  }else{
+    sqlite3_int64 docid;
+    *pnOut = sqlite3Fts3GetVarint(aSource, &docid);
+    *ppOut = sqlite3_malloc(*pnOut);
+    if( !*ppOut ) return SQLITE_NOMEM;
+    sqlite3Fts3PutVarint(*ppOut, docid);
+  }
+
+  return SQLITE_OK;
+}
+
+int sqlite3Fts3SegReaderCursor(
+  Fts3Table *p,                   /* FTS3 table handle */
+  int iLevel,                     /* Level of segments to scan */
+  const char *zTerm,              /* Term to query for */
+  int nTerm,                      /* Size of zTerm in bytes */
+  int isPrefix,                   /* True for a prefix search */
+  int isScan,                     /* True to scan from zTerm to EOF */
+  Fts3SegReaderCursor *pCsr       /* Cursor object to populate */
+){
+  int rc = SQLITE_OK;
+  int rc2;
+  int iAge = 0;
+  sqlite3_stmt *pStmt = 0;
+  Fts3SegReader *pPending = 0;
+
+  assert( iLevel==FTS3_SEGCURSOR_ALL 
+      ||  iLevel==FTS3_SEGCURSOR_PENDING 
+      ||  iLevel>=0
+  );
+  assert( FTS3_SEGCURSOR_PENDING<0 );
+  assert( FTS3_SEGCURSOR_ALL<0 );
+  assert( iLevel==FTS3_SEGCURSOR_ALL || (zTerm==0 && isPrefix==1) );
+  assert( isPrefix==0 || isScan==0 );
+
+
+  memset(pCsr, 0, sizeof(Fts3SegReaderCursor));
+
+  /* If iLevel is less than 0, include a seg-reader for the pending-terms. */
+  assert( isScan==0 || fts3HashCount(&p->pendingTerms)==0 );
+  if( iLevel<0 && isScan==0 ){
+    rc = sqlite3Fts3SegReaderPending(p, zTerm, nTerm, isPrefix, &pPending);
+    if( rc==SQLITE_OK && pPending ){
+      int nByte = (sizeof(Fts3SegReader *) * 16);
+      pCsr->apSegment = (Fts3SegReader **)sqlite3_malloc(nByte);
+      if( pCsr->apSegment==0 ){
+        rc = SQLITE_NOMEM;
+      }else{
+        pCsr->apSegment[0] = pPending;
+        pCsr->nSegment = 1;
+        pPending = 0;
+      }
+    }
+  }
+
+  if( iLevel!=FTS3_SEGCURSOR_PENDING ){
+    if( rc==SQLITE_OK ){
+      rc = sqlite3Fts3AllSegdirs(p, iLevel, &pStmt);
+    }
+    while( rc==SQLITE_OK && SQLITE_ROW==(rc = sqlite3_step(pStmt)) ){
+
+      /* Read the values returned by the SELECT into local variables. */
+      sqlite3_int64 iStartBlock = sqlite3_column_int64(pStmt, 1);
+      sqlite3_int64 iLeavesEndBlock = sqlite3_column_int64(pStmt, 2);
+      sqlite3_int64 iEndBlock = sqlite3_column_int64(pStmt, 3);
+      int nRoot = sqlite3_column_bytes(pStmt, 4);
+      char const *zRoot = sqlite3_column_blob(pStmt, 4);
+
+      /* If nSegment is a multiple of 16 the array needs to be extended. */
+      if( (pCsr->nSegment%16)==0 ){
+        Fts3SegReader **apNew;
+        int nByte = (pCsr->nSegment + 16)*sizeof(Fts3SegReader*);
+        apNew = (Fts3SegReader **)sqlite3_realloc(pCsr->apSegment, nByte);
+        if( !apNew ){
+          rc = SQLITE_NOMEM;
+          goto finished;
+        }
+        pCsr->apSegment = apNew;
+      }
+
+      /* If zTerm is not NULL, and this segment is not stored entirely on its
+      ** root node, the range of leaves scanned can be reduced. Do this. */
+      if( iStartBlock && zTerm ){
+        sqlite3_int64 *pi = (isPrefix ? &iLeavesEndBlock : 0);
+        rc = fts3SelectLeaf(p, zTerm, nTerm, zRoot, nRoot, &iStartBlock, pi);
+        if( rc!=SQLITE_OK ) goto finished;
+        if( isPrefix==0 && isScan==0 ) iLeavesEndBlock = iStartBlock;
+      }
+ 
+      rc = sqlite3Fts3SegReaderNew(iAge, iStartBlock, iLeavesEndBlock,
+          iEndBlock, zRoot, nRoot, &pCsr->apSegment[pCsr->nSegment]
+      );
+      if( rc!=SQLITE_OK ) goto finished;
+      pCsr->nSegment++;
+      iAge++;
+    }
+  }
+
+ finished:
+  rc2 = sqlite3_reset(pStmt);
+  if( rc==SQLITE_DONE ) rc = rc2;
+  sqlite3Fts3SegReaderFree(pPending);
+
+  return rc;
+}
+
+
+static int fts3TermSegReaderCursor(
+  Fts3Cursor *pCsr,               /* Virtual table cursor handle */
+  const char *zTerm,              /* Term to query for */
+  int nTerm,                      /* Size of zTerm in bytes */
+  int isPrefix,                   /* True for a prefix search */
+  Fts3SegReaderCursor **ppSegcsr  /* OUT: Allocated seg-reader cursor */
+){
+  Fts3SegReaderCursor *pSegcsr;   /* Object to allocate and return */
+  int rc = SQLITE_NOMEM;          /* Return code */
+
+  pSegcsr = sqlite3_malloc(sizeof(Fts3SegReaderCursor));
+  if( pSegcsr ){
+    Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
+    int i;
+    int nCost = 0;
+    rc = sqlite3Fts3SegReaderCursor(
+        p, FTS3_SEGCURSOR_ALL, zTerm, nTerm, isPrefix, 0, pSegcsr);
+  
+    for(i=0; rc==SQLITE_OK && i<pSegcsr->nSegment; i++){
+      rc = sqlite3Fts3SegReaderCost(pCsr, pSegcsr->apSegment[i], &nCost);
+    }
+    pSegcsr->nCost = nCost;
+  }
+
+  *ppSegcsr = pSegcsr;
+  return rc;
+}
+
+static void fts3SegReaderCursorFree(Fts3SegReaderCursor *pSegcsr){
+  sqlite3Fts3SegReaderFinish(pSegcsr);
+  sqlite3_free(pSegcsr);
+}
+
+/*
+** This function retreives the doclist for the specified term (or term
+** prefix) from the database. 
+**
+** The returned doclist may be in one of two formats, depending on the 
+** value of parameter isReqPos. If isReqPos is zero, then the doclist is
+** a sorted list of delta-compressed docids (a bare doclist). If isReqPos
+** is non-zero, then the returned list is in the same format as is stored 
+** in the database without the found length specifier at the start of on-disk
+** doclists.
+*/
+static int fts3TermSelect(
+  Fts3Table *p,                   /* Virtual table handle */
+  Fts3PhraseToken *pTok,          /* Token to query for */
+  int iColumn,                    /* Column to query (or -ve for all columns) */
+  int isReqPos,                   /* True to include position lists in output */
+  int *pnOut,                     /* OUT: Size of buffer at *ppOut */
+  char **ppOut                    /* OUT: Malloced result buffer */
+){
+  int rc;                         /* Return code */
+  Fts3SegReaderCursor *pSegcsr;   /* Seg-reader cursor for this term */
+  TermSelect tsc;                 /* Context object for fts3TermSelectCb() */
+  Fts3SegFilter filter;           /* Segment term filter configuration */
+
+  pSegcsr = pTok->pSegcsr;
+  memset(&tsc, 0, sizeof(TermSelect));
+  tsc.isReqPos = isReqPos;
+
+  filter.flags = FTS3_SEGMENT_IGNORE_EMPTY 
+        | (pTok->isPrefix ? FTS3_SEGMENT_PREFIX : 0)
+        | (isReqPos ? FTS3_SEGMENT_REQUIRE_POS : 0)
+        | (iColumn<p->nColumn ? FTS3_SEGMENT_COLUMN_FILTER : 0);
+  filter.iCol = iColumn;
+  filter.zTerm = pTok->z;
+  filter.nTerm = pTok->n;
+
+  rc = sqlite3Fts3SegReaderStart(p, pSegcsr, &filter);
+  while( SQLITE_OK==rc
+      && SQLITE_ROW==(rc = sqlite3Fts3SegReaderStep(p, pSegcsr)) 
+  ){
+    rc = fts3TermSelectCb(p, (void *)&tsc, 
+        pSegcsr->zTerm, pSegcsr->nTerm, pSegcsr->aDoclist, pSegcsr->nDoclist
+    );
+  }
+
+  if( rc==SQLITE_OK ){
+    rc = fts3TermSelectMerge(&tsc);
+  }
+  if( rc==SQLITE_OK ){
+    *ppOut = tsc.aaOutput[0];
+    *pnOut = tsc.anOutput[0];
+  }else{
+    int i;
+    for(i=0; i<SizeofArray(tsc.aaOutput); i++){
+      sqlite3_free(tsc.aaOutput[i]);
+    }
+  }
+
+  fts3SegReaderCursorFree(pSegcsr);
+  pTok->pSegcsr = 0;
+  return rc;
+}
+
+/*
+** This function counts the total number of docids in the doclist stored
+** in buffer aList[], size nList bytes.
+**
+** If the isPoslist argument is true, then it is assumed that the doclist
+** contains a position-list following each docid. Otherwise, it is assumed
+** that the doclist is simply a list of docids stored as delta encoded 
+** varints.
+*/
+static int fts3DoclistCountDocids(int isPoslist, char *aList, int nList){
+  int nDoc = 0;                   /* Return value */
+  if( aList ){
+    char *aEnd = &aList[nList];   /* Pointer to one byte after EOF */
+    char *p = aList;              /* Cursor */
+    if( !isPoslist ){
+      /* The number of docids in the list is the same as the number of 
+      ** varints. In FTS3 a varint consists of a single byte with the 0x80 
+      ** bit cleared and zero or more bytes with the 0x80 bit set. So to
+      ** count the varints in the buffer, just count the number of bytes
+      ** with the 0x80 bit clear.  */
+      while( p<aEnd ) nDoc += (((*p++)&0x80)==0);
     }else{
-      z[j++] = z[i];
-    }
-  }
-}
-
-/*
-** The input azIn is a NULL-terminated list of tokens.  Remove the first
-** token and all punctuation tokens.  Remove the quotes from
-** around string literal tokens.
-**
-** Example:
-**
-**     input:      tokenize chinese ( 'simplifed' , 'mixed' )
-**     output:     chinese simplifed mixed
-**
-** Another example:
-**
-**     input:      delimiters ( '[' , ']' , '...' )
-**     output:     [ ] ...
-*/
-static void tokenListToIdList(char **azIn){
-  int i, j;
-  if( azIn ){
-    for(i=0, j=-1; azIn[i]; i++){
-      if( safe_isalnum(azIn[i][0]) || azIn[i][1] ){
-        dequoteString(azIn[i]);
-        if( j>=0 ){
-          azIn[j] = azIn[i];
+      while( p<aEnd ){
+        nDoc++;
+        while( (*p++)&0x80 );     /* Skip docid varint */
+        fts3PoslistCopy(0, &p);   /* Skip over position list */
+      }
+    }
+  }
+
+  return nDoc;
+}
+
+/*
+** Call sqlite3Fts3DeferToken() for each token in the expression pExpr.
+*/
+static int fts3DeferExpression(Fts3Cursor *pCsr, Fts3Expr *pExpr){
+  int rc = SQLITE_OK;
+  if( pExpr ){
+    rc = fts3DeferExpression(pCsr, pExpr->pLeft);
+    if( rc==SQLITE_OK ){
+      rc = fts3DeferExpression(pCsr, pExpr->pRight);
+    }
+    if( pExpr->eType==FTSQUERY_PHRASE ){
+      int iCol = pExpr->pPhrase->iColumn;
+      int i;
+      for(i=0; rc==SQLITE_OK && i<pExpr->pPhrase->nToken; i++){
+        Fts3PhraseToken *pToken = &pExpr->pPhrase->aToken[i];
+        if( pToken->pDeferred==0 ){
+          rc = sqlite3Fts3DeferToken(pCsr, pToken, iCol);
         }
-        j++;
-      }
-    }
-    azIn[j] = 0;
-  }
-}
-
-
-/*
-** Find the first alphanumeric token in the string zIn.  Null-terminate
-** this token.  Remove any quotation marks.  And return a pointer to
-** the result.
-*/
-static char *firstToken(char *zIn, char **pzTail){
-  int n, ttype;
-  while(1){
-    n = ftsGetToken(zIn, &ttype);
-    if( ttype==TOKEN_SPACE ){
-      zIn += n;
-    }else if( ttype==TOKEN_EOF ){
-      *pzTail = zIn;
-      return 0;
+      }
+    }
+  }
+  return rc;
+}
+
+/*
+** This function removes the position information from a doclist. When
+** called, buffer aList (size *pnList bytes) contains a doclist that includes
+** position information. This function removes the position information so
+** that aList contains only docids, and adjusts *pnList to reflect the new
+** (possibly reduced) size of the doclist.
+*/
+static void fts3DoclistStripPositions(
+  char *aList,                    /* IN/OUT: Buffer containing doclist */
+  int *pnList                     /* IN/OUT: Size of doclist in bytes */
+){
+  if( aList ){
+    char *aEnd = &aList[*pnList]; /* Pointer to one byte after EOF */
+    char *p = aList;              /* Input cursor */
+    char *pOut = aList;           /* Output cursor */
+  
+    while( p<aEnd ){
+      sqlite3_int64 delta;
+      p += sqlite3Fts3GetVarint(p, &delta);
+      fts3PoslistCopy(0, &p);
+      pOut += sqlite3Fts3PutVarint(pOut, delta);
+    }
+
+    *pnList = (int)(pOut - aList);
+  }
+}
+
+/* 
+** Return a DocList corresponding to the phrase *pPhrase.
+**
+** If this function returns SQLITE_OK, but *pnOut is set to a negative value,
+** then no tokens in the phrase were looked up in the full-text index. This
+** is only possible when this function is called from within xFilter(). The
+** caller should assume that all documents match the phrase. The actual
+** filtering will take place in xNext().
+*/
+static int fts3PhraseSelect(
+  Fts3Cursor *pCsr,               /* Virtual table cursor handle */
+  Fts3Phrase *pPhrase,            /* Phrase to return a doclist for */
+  int isReqPos,                   /* True if output should contain positions */
+  char **paOut,                   /* OUT: Pointer to malloc'd result buffer */
+  int *pnOut                      /* OUT: Size of buffer at *paOut */
+){
+  char *pOut = 0;
+  int nOut = 0;
+  int rc = SQLITE_OK;
+  int ii;
+  int iCol = pPhrase->iColumn;
+  int isTermPos = (pPhrase->nToken>1 || isReqPos);
+  Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
+  int isFirst = 1;
+
+  int iPrevTok = 0;
+  int nDoc = 0;
+
+  /* If this is an xFilter() evaluation, create a segment-reader for each
+  ** phrase token. Or, if this is an xNext() or snippet/offsets/matchinfo
+  ** evaluation, only create segment-readers if there are no Fts3DeferredToken
+  ** objects attached to the phrase-tokens.
+  */
+  for(ii=0; ii<pPhrase->nToken; ii++){
+    Fts3PhraseToken *pTok = &pPhrase->aToken[ii];
+    if( pTok->pSegcsr==0 ){
+      if( (pCsr->eEvalmode==FTS3_EVAL_FILTER)
+       || (pCsr->eEvalmode==FTS3_EVAL_NEXT && pCsr->pDeferred==0) 
+       || (pCsr->eEvalmode==FTS3_EVAL_MATCHINFO && pTok->bFulltext) 
+      ){
+        rc = fts3TermSegReaderCursor(
+            pCsr, pTok->z, pTok->n, pTok->isPrefix, &pTok->pSegcsr
+        );
+        if( rc!=SQLITE_OK ) return rc;
+      }
+    }
+  }
+
+  for(ii=0; ii<pPhrase->nToken; ii++){
+    Fts3PhraseToken *pTok;        /* Token to find doclist for */
+    int iTok = 0;                 /* The token being queried this iteration */
+    char *pList = 0;              /* Pointer to token doclist */
+    int nList = 0;                /* Size of buffer at pList */
+
+    /* Select a token to process. If this is an xFilter() call, then tokens 
+    ** are processed in order from least to most costly. Otherwise, tokens 
+    ** are processed in the order in which they occur in the phrase.
+    */
+    if( pCsr->eEvalmode==FTS3_EVAL_MATCHINFO ){
+      assert( isReqPos );
+      iTok = ii;
+      pTok = &pPhrase->aToken[iTok];
+      if( pTok->bFulltext==0 ) continue;
+    }else if( pCsr->eEvalmode==FTS3_EVAL_NEXT || isReqPos ){
+      iTok = ii;
+      pTok = &pPhrase->aToken[iTok];
     }else{
-      zIn[n] = 0;
-      *pzTail = &zIn[1];
-      dequoteString(zIn);
-      return zIn;
-    }
-  }
-  /*NOTREACHED*/
-}
-
-/* Return true if...
-**
-**   *  s begins with the string t, ignoring case
-**   *  s is longer than t
-**   *  The first character of s beyond t is not a alphanumeric
-** 
-** Ignore leading space in *s.
-**
-** To put it another way, return true if the first token of
-** s[] is t[].
-*/
-static int startsWith(const char *s, const char *t){
-  while( safe_isspace(*s) ){ s++; }
-  while( *t ){
-    if( safe_tolower(*s++)!=safe_tolower(*t++) ) return 0;
-  }
-  return *s!='_' && !safe_isalnum(*s);
-}
-
-/*
-** An instance of this structure defines the "spec" of a
-** full text index.  This structure is populated by parseSpec
-** and use by fulltextConnect and fulltextCreate.
-*/
-typedef struct TableSpec {
-  const char *zDb;         /* Logical database name */
-  const char *zName;       /* Name of the full-text index */
-  int nColumn;             /* Number of columns to be indexed */
-  char **azColumn;         /* Original names of columns to be indexed */
-  char **azContentColumn;  /* Column names for %_content */
-  char **azTokenizer;      /* Name of tokenizer and its arguments */
-} TableSpec;
-
-/*
-** Reclaim all of the memory used by a TableSpec
-*/
-static void clearTableSpec(TableSpec *p) {
-  sqlite3_free(p->azColumn);
-  sqlite3_free(p->azContentColumn);
-  sqlite3_free(p->azTokenizer);
-}
-
-/* Parse a CREATE VIRTUAL TABLE statement, which looks like this:
- *
- * CREATE VIRTUAL TABLE email
- *        USING fts3(subject, body, tokenize mytokenizer(myarg))
- *
- * We return parsed information in a TableSpec structure.
- * 
- */
-static int parseSpec(TableSpec *pSpec, int argc, const char *const*argv,
-                     char**pzErr){
-  int i, n;
-  char *z, *zDummy;
-  char **azArg;
-  const char *zTokenizer = 0;    /* argv[] entry describing the tokenizer */
-
-  assert( argc>=3 );
-  /* Current interface:
-  ** argv[0] - module name
-  ** argv[1] - database name
-  ** argv[2] - table name
-  ** argv[3..] - columns, optionally followed by tokenizer specification
-  **             and snippet delimiters specification.
-  */
-
-  /* Make a copy of the complete argv[][] array in a single allocation.
-  ** The argv[][] array is read-only and transient.  We can write to the
-  ** copy in order to modify things and the copy is persistent.
-  */
-  CLEAR(pSpec);
-  for(i=n=0; i<argc; i++){
-    n += strlen(argv[i]) + 1;
-  }
-  azArg = sqlite3_malloc( sizeof(char*)*argc + n );
-  if( azArg==0 ){
-    return SQLITE_NOMEM;
-  }
-  z = (char*)&azArg[argc];
-  for(i=0; i<argc; i++){
-    azArg[i] = z;
-    strcpy(z, argv[i]);
-    z += strlen(z)+1;
-  }
-
-  /* Identify the column names and the tokenizer and delimiter arguments
-  ** in the argv[][] array.
-  */
-  pSpec->zDb = azArg[1];
-  pSpec->zName = azArg[2];
-  pSpec->nColumn = 0;
-  pSpec->azColumn = azArg;
-  zTokenizer = "tokenize simple";
-  for(i=3; i<argc; ++i){
-    if( startsWith(azArg[i],"tokenize") ){
-      zTokenizer = azArg[i];
+      int nMinCost = 0x7FFFFFFF;
+      int jj;
+
+      /* Find the remaining token with the lowest cost. */
+      for(jj=0; jj<pPhrase->nToken; jj++){
+        Fts3SegReaderCursor *pSegcsr = pPhrase->aToken[jj].pSegcsr;
+        if( pSegcsr && pSegcsr->nCost<nMinCost ){
+          iTok = jj;
+          nMinCost = pSegcsr->nCost;
+        }
+      }
+      pTok = &pPhrase->aToken[iTok];
+
+      /* This branch is taken if it is determined that loading the doclist
+      ** for the next token would require more IO than loading all documents
+      ** currently identified by doclist pOut/nOut. No further doclists will
+      ** be loaded from the full-text index for this phrase.
+      */
+      if( nMinCost>nDoc && ii>0 ){
+        rc = fts3DeferExpression(pCsr, pCsr->pExpr);
+        break;
+      }
+    }
+
+    if( pCsr->eEvalmode==FTS3_EVAL_NEXT && pTok->pDeferred ){
+      rc = fts3DeferredTermSelect(pTok->pDeferred, isTermPos, &nList, &pList);
     }else{
-      z = azArg[pSpec->nColumn] = firstToken(azArg[i], &zDummy);
-      pSpec->nColumn++;
-    }
-  }
-  if( pSpec->nColumn==0 ){
-    azArg[0] = "content";
-    pSpec->nColumn = 1;
-  }
-
-  /*
-  ** Construct the list of content column names.
-  **
-  ** Each content column name will be of the form cNNAAAA
-  ** where NN is the column number and AAAA is the sanitized
-  ** column name.  "sanitized" means that special characters are
-  ** converted to "_".  The cNN prefix guarantees that all column
-  ** names are unique.
-  **
-  ** The AAAA suffix is not strictly necessary.  It is included
-  ** for the convenience of people who might examine the generated
-  ** %_content table and wonder what the columns are used for.
-  */
-  pSpec->azContentColumn = sqlite3_malloc( pSpec->nColumn * sizeof(char *) );
-  if( pSpec->azContentColumn==0 ){
-    clearTableSpec(pSpec);
-    return SQLITE_NOMEM;
-  }
-  for(i=0; i<pSpec->nColumn; i++){
-    char *p;
-    pSpec->azContentColumn[i] = sqlite3_mprintf("c%d%s", i, azArg[i]);
-    for (p = pSpec->azContentColumn[i]; *p ; ++p) {
-      if( !safe_isalnum(*p) ) *p = '_';
-    }
-  }
-
-  /*
-  ** Parse the tokenizer specification string.
-  */
-  pSpec->azTokenizer = tokenizeString(zTokenizer, &n);
-  tokenListToIdList(pSpec->azTokenizer);
-
-  return SQLITE_OK;
-}
-
-/*
-** Generate a CREATE TABLE statement that describes the schema of
-** the virtual table.  Return a pointer to this schema string.
-**
-** Space is obtained from sqlite3_mprintf() and should be freed
-** using sqlite3_free().
-*/
-static char *fulltextSchema(
-  int nColumn,                  /* Number of columns */
-  const char *const* azColumn,  /* List of columns */
-  const char *zTableName        /* Name of the table */
-){
-  int i;
-  char *zSchema, *zNext;
-  const char *zSep = "(";
-  zSchema = sqlite3_mprintf("CREATE TABLE x");
-  for(i=0; i<nColumn; i++){
-    zNext = sqlite3_mprintf("%s%s%Q", zSchema, zSep, azColumn[i]);
-    sqlite3_free(zSchema);
-    zSchema = zNext;
-    zSep = ",";
-  }
-  zNext = sqlite3_mprintf("%s,%Q HIDDEN", zSchema, zTableName);
-  sqlite3_free(zSchema);
-  zSchema = zNext;
-  zNext = sqlite3_mprintf("%s,docid HIDDEN)", zSchema);
-  sqlite3_free(zSchema);
-  return zNext;
-}
-
-/*
-** Build a new sqlite3_vtab structure that will describe the
-** fulltext index defined by spec.
-*/
-static int constructVtab(
-  sqlite3 *db,              /* The SQLite database connection */
-  fts3Hash *pHash,          /* Hash table containing tokenizers */
-  TableSpec *spec,          /* Parsed spec information from parseSpec() */
-  sqlite3_vtab **ppVTab,    /* Write the resulting vtab structure here */
-  char **pzErr              /* Write any error message here */
-){
-  int rc;
-  int n;
-  fulltext_vtab *v = 0;
-  const sqlite3_tokenizer_module *m = NULL;
-  char *schema;
-
-  char const *zTok;         /* Name of tokenizer to use for this fts table */
-  int nTok;                 /* Length of zTok, including nul terminator */
-
-  v = (fulltext_vtab *) sqlite3_malloc(sizeof(fulltext_vtab));
-  if( v==0 ) return SQLITE_NOMEM;
-  CLEAR(v);
-  /* sqlite will initialize v->base */
-  v->db = db;
-  v->zDb = spec->zDb;       /* Freed when azColumn is freed */
-  v->zName = spec->zName;   /* Freed when azColumn is freed */
-  v->nColumn = spec->nColumn;
-  v->azContentColumn = spec->azContentColumn;
-  spec->azContentColumn = 0;
-  v->azColumn = spec->azColumn;
-  spec->azColumn = 0;
-
-  if( spec->azTokenizer==0 ){
-    return SQLITE_NOMEM;
-  }
-
-  zTok = spec->azTokenizer[0]; 
-  if( !zTok ){
-    zTok = "simple";
-  }
-  nTok = strlen(zTok)+1;
-
-  m = (sqlite3_tokenizer_module *)sqlite3Fts3HashFind(pHash, zTok, nTok);
-  if( !m ){
-    *pzErr = sqlite3_mprintf("unknown tokenizer: %s", spec->azTokenizer[0]);
-    rc = SQLITE_ERROR;
-    goto err;
-  }
-
-  for(n=0; spec->azTokenizer[n]; n++){}
-  if( n ){
-    rc = m->xCreate(n-1, (const char*const*)&spec->azTokenizer[1],
-                    &v->pTokenizer);
+      if( pTok->pSegcsr ){
+        rc = fts3TermSelect(p, pTok, iCol, isTermPos, &nList, &pList);
+      }
+      pTok->bFulltext = 1;
+    }
+    assert( rc!=SQLITE_OK || pCsr->eEvalmode || pTok->pSegcsr==0 );
+    if( rc!=SQLITE_OK ) break;
+
+    if( isFirst ){
+      pOut = pList;
+      nOut = nList;
+      if( pCsr->eEvalmode==FTS3_EVAL_FILTER && pPhrase->nToken>1 ){
+        nDoc = fts3DoclistCountDocids(1, pOut, nOut);
+      }
+      isFirst = 0;
+      iPrevTok = iTok;
+    }else{
+      /* Merge the new term list and the current output. */
+      char *aLeft, *aRight;
+      int nLeft, nRight;
+      int nDist;
+      int mt;
+
+      /* If this is the final token of the phrase, and positions were not
+      ** requested by the caller, use MERGE_PHRASE instead of POS_PHRASE.
+      ** This drops the position information from the output list.
+      */
+      mt = MERGE_POS_PHRASE;
+      if( ii==pPhrase->nToken-1 && !isReqPos ) mt = MERGE_PHRASE;
+
+      assert( iPrevTok!=iTok );
+      if( iPrevTok<iTok ){
+        aLeft = pOut;
+        nLeft = nOut;
+        aRight = pList;
+        nRight = nList;
+        nDist = iTok-iPrevTok;
+        iPrevTok = iTok;
+      }else{
+        aRight = pOut;
+        nRight = nOut;
+        aLeft = pList;
+        nLeft = nList;
+        nDist = iPrevTok-iTok;
+      }
+      pOut = aRight;
+      fts3DoclistMerge(
+          mt, nDist, 0, pOut, &nOut, aLeft, nLeft, aRight, nRight, &nDoc
+      );
+      sqlite3_free(aLeft);
+    }
+    assert( nOut==0 || pOut!=0 );
+  }
+
+  if( rc==SQLITE_OK ){
+    if( ii!=pPhrase->nToken ){
+      assert( pCsr->eEvalmode==FTS3_EVAL_FILTER && isReqPos==0 );
+      fts3DoclistStripPositions(pOut, &nOut);
+    }
+    *paOut = pOut;
+    *pnOut = nOut;
   }else{
-    rc = m->xCreate(0, 0, &v->pTokenizer);
-  }
-  if( rc!=SQLITE_OK ) goto err;
-  v->pTokenizer->pModule = m;
-
-  /* TODO: verify the existence of backing tables foo_content, foo_term */
-
-  schema = fulltextSchema(v->nColumn, (const char*const*)v->azColumn,
-                          spec->zName);
-  rc = sqlite3_declare_vtab(db, schema);
-  sqlite3_free(schema);
-  if( rc!=SQLITE_OK ) goto err;
-
-  memset(v->pFulltextStatements, 0, sizeof(v->pFulltextStatements));
-
-  /* Indicate that the buffer is not live. */
-  v->nPendingData = -1;
-
-  *ppVTab = &v->base;
-  FTSTRACE(("FTS3 Connect %p\n", v));
-
+    sqlite3_free(pOut);
+  }
   return rc;
-
-err:
-  fulltext_vtab_destroy(v);
+}
+
+/*
+** This function merges two doclists according to the requirements of a
+** NEAR operator.
+**
+** Both input doclists must include position information. The output doclist 
+** includes position information if the first argument to this function
+** is MERGE_POS_NEAR, or does not if it is MERGE_NEAR.
+*/
+static int fts3NearMerge(
+  int mergetype,                  /* MERGE_POS_NEAR or MERGE_NEAR */
+  int nNear,                      /* Parameter to NEAR operator */
+  int nTokenLeft,                 /* Number of tokens in LHS phrase arg */
+  char *aLeft,                    /* Doclist for LHS (incl. positions) */
+  int nLeft,                      /* Size of LHS doclist in bytes */
+  int nTokenRight,                /* As nTokenLeft */
+  char *aRight,                   /* As aLeft */
+  int nRight,                     /* As nRight */
+  char **paOut,                   /* OUT: Results of merge (malloced) */
+  int *pnOut                      /* OUT: Sized of output buffer */
+){
+  char *aOut;                     /* Buffer to write output doclist to */
+  int rc;                         /* Return code */
+
+  assert( mergetype==MERGE_POS_NEAR || MERGE_NEAR );
+
+  aOut = sqlite3_malloc(nLeft+nRight+1);
+  if( aOut==0 ){
+    rc = SQLITE_NOMEM;
+  }else{
+    rc = fts3DoclistMerge(mergetype, nNear+nTokenRight, nNear+nTokenLeft, 
+      aOut, pnOut, aLeft, nLeft, aRight, nRight, 0
+    );
+    if( rc!=SQLITE_OK ){
+      sqlite3_free(aOut);
+      aOut = 0;
+    }
+  }
+
+  *paOut = aOut;
   return rc;
 }
 
-static int fulltextConnect(
-  sqlite3 *db,
-  void *pAux,
-  int argc, const char *const*argv,
-  sqlite3_vtab **ppVTab,
-  char **pzErr
-){
-  TableSpec spec;
-  int rc = parseSpec(&spec, argc, argv, pzErr);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = constructVtab(db, (fts3Hash *)pAux, &spec, ppVTab, pzErr);
-  clearTableSpec(&spec);
+/*
+** This function is used as part of the processing for the snippet() and
+** offsets() functions.
+**
+** Both pLeft and pRight are expression nodes of type FTSQUERY_PHRASE. Both
+** have their respective doclists (including position information) loaded
+** in Fts3Expr.aDoclist/nDoclist. This function removes all entries from
+** each doclist that are not within nNear tokens of a corresponding entry
+** in the other doclist.
+*/
+int sqlite3Fts3ExprNearTrim(Fts3Expr *pLeft, Fts3Expr *pRight, int nNear){
+  int rc;                         /* Return code */
+
+  assert( pLeft->eType==FTSQUERY_PHRASE );
+  assert( pRight->eType==FTSQUERY_PHRASE );
+  assert( pLeft->isLoaded && pRight->isLoaded );
+
+  if( pLeft->aDoclist==0 || pRight->aDoclist==0 ){
+    sqlite3_free(pLeft->aDoclist);
+    sqlite3_free(pRight->aDoclist);
+    pRight->aDoclist = 0;
+    pLeft->aDoclist = 0;
+    rc = SQLITE_OK;
+  }else{
+    char *aOut;                   /* Buffer in which to assemble new doclist */
+    int nOut;                     /* Size of buffer aOut in bytes */
+
+    rc = fts3NearMerge(MERGE_POS_NEAR, nNear, 
+        pLeft->pPhrase->nToken, pLeft->aDoclist, pLeft->nDoclist,
+        pRight->pPhrase->nToken, pRight->aDoclist, pRight->nDoclist,
+        &aOut, &nOut
+    );
+    if( rc!=SQLITE_OK ) return rc;
+    sqlite3_free(pRight->aDoclist);
+    pRight->aDoclist = aOut;
+    pRight->nDoclist = nOut;
+
+    rc = fts3NearMerge(MERGE_POS_NEAR, nNear, 
+        pRight->pPhrase->nToken, pRight->aDoclist, pRight->nDoclist,
+        pLeft->pPhrase->nToken, pLeft->aDoclist, pLeft->nDoclist,
+        &aOut, &nOut
+    );
+    sqlite3_free(pLeft->aDoclist);
+    pLeft->aDoclist = aOut;
+    pLeft->nDoclist = nOut;
+  }
   return rc;
 }
 
-/* The %_content table holds the text of each document, with
-** the docid column exposed as the SQLite rowid for the table.
-*/
-/* TODO(shess) This comment needs elaboration to match the updated
-** code.  Work it into the top-of-file comment at that time.
-*/
-static int fulltextCreate(sqlite3 *db, void *pAux,
-                          int argc, const char * const *argv,
-                          sqlite3_vtab **ppVTab, char **pzErr){
-  int rc;
-  TableSpec spec;
-  StringBuffer schema;
-  FTSTRACE(("FTS3 Create\n"));
-
-  rc = parseSpec(&spec, argc, argv, pzErr);
-  if( rc!=SQLITE_OK ) return rc;
-
-  initStringBuffer(&schema);
-  append(&schema, "CREATE TABLE %_content(");
-  append(&schema, "  docid INTEGER PRIMARY KEY,");
-  appendList(&schema, spec.nColumn, spec.azContentColumn);
-  append(&schema, ")");
-  rc = sql_exec(db, spec.zDb, spec.zName, stringBufferData(&schema));
-  stringBufferDestroy(&schema);
-  if( rc!=SQLITE_OK ) goto out;
-
-  rc = sql_exec(db, spec.zDb, spec.zName,
-                "create table %_segments("
-                "  blockid INTEGER PRIMARY KEY,"
-                "  block blob"
-                ");"
-                );
-  if( rc!=SQLITE_OK ) goto out;
-
-  rc = sql_exec(db, spec.zDb, spec.zName,
-                "create table %_segdir("
-                "  level integer,"
-                "  idx integer,"
-                "  start_block integer,"
-                "  leaves_end_block integer,"
-                "  end_block integer,"
-                "  root blob,"
-                "  primary key(level, idx)"
-                ");");
-  if( rc!=SQLITE_OK ) goto out;
-
-  rc = constructVtab(db, (fts3Hash *)pAux, &spec, ppVTab, pzErr);
-
-out:
-  clearTableSpec(&spec);
+
+/*
+** Allocate an Fts3SegReaderArray for each token in the expression pExpr. 
+** The allocated objects are stored in the Fts3PhraseToken.pArray member
+** variables of each token structure.
+*/
+static int fts3ExprAllocateSegReaders(
+  Fts3Cursor *pCsr,               /* FTS3 table */
+  Fts3Expr *pExpr,                /* Expression to create seg-readers for */
+  int *pnExpr                     /* OUT: Number of AND'd expressions */
+){
+  int rc = SQLITE_OK;             /* Return code */
+
+  assert( pCsr->eEvalmode==FTS3_EVAL_FILTER );
+  if( pnExpr && pExpr->eType!=FTSQUERY_AND ){
+    (*pnExpr)++;
+    pnExpr = 0;
+  }
+
+  if( pExpr->eType==FTSQUERY_PHRASE ){
+    Fts3Phrase *pPhrase = pExpr->pPhrase;
+    int ii;
+
+    for(ii=0; rc==SQLITE_OK && ii<pPhrase->nToken; ii++){
+      Fts3PhraseToken *pTok = &pPhrase->aToken[ii];
+      if( pTok->pSegcsr==0 ){
+        rc = fts3TermSegReaderCursor(
+            pCsr, pTok->z, pTok->n, pTok->isPrefix, &pTok->pSegcsr
+        );
+      }
+    }
+  }else{ 
+    rc = fts3ExprAllocateSegReaders(pCsr, pExpr->pLeft, pnExpr);
+    if( rc==SQLITE_OK ){
+      rc = fts3ExprAllocateSegReaders(pCsr, pExpr->pRight, pnExpr);
+    }
+  }
   return rc;
 }
 
-/* Decide how to handle an SQL query. */
-static int fulltextBestIndex(sqlite3_vtab *pVTab, sqlite3_index_info *pInfo){
-  fulltext_vtab *v = (fulltext_vtab *)pVTab;
-  int i;
-  FTSTRACE(("FTS3 BestIndex\n"));
-
-  for(i=0; i<pInfo->nConstraint; ++i){
-    const struct sqlite3_index_constraint *pConstraint;
-    pConstraint = &pInfo->aConstraint[i];
-    if( pConstraint->usable ) {
-      if( (pConstraint->iColumn==-1 || pConstraint->iColumn==v->nColumn+1) &&
-          pConstraint->op==SQLITE_INDEX_CONSTRAINT_EQ ){
-        pInfo->idxNum = QUERY_DOCID;      /* lookup by docid */
-        FTSTRACE(("FTS3 QUERY_DOCID\n"));
-      } else if( pConstraint->iColumn>=0 && pConstraint->iColumn<=v->nColumn &&
-                 pConstraint->op==SQLITE_INDEX_CONSTRAINT_MATCH ){
-        /* full-text search */
-        pInfo->idxNum = QUERY_FULLTEXT + pConstraint->iColumn;
-        FTSTRACE(("FTS3 QUERY_FULLTEXT %d\n", pConstraint->iColumn));
-      } else continue;
-
-      pInfo->aConstraintUsage[i].argvIndex = 1;
-      pInfo->aConstraintUsage[i].omit = 1;
-
-      /* An arbitrary value for now.
-       * TODO: Perhaps docid matches should be considered cheaper than
-       * full-text searches. */
-      pInfo->estimatedCost = 1.0;   
-
-      return SQLITE_OK;
-    }
-  }
-  pInfo->idxNum = QUERY_GENERIC;
-  return SQLITE_OK;
-}
-
-static int fulltextDisconnect(sqlite3_vtab *pVTab){
-  FTSTRACE(("FTS3 Disconnect %p\n", pVTab));
-  fulltext_vtab_destroy((fulltext_vtab *)pVTab);
-  return SQLITE_OK;
-}
-
-static int fulltextDestroy(sqlite3_vtab *pVTab){
-  fulltext_vtab *v = (fulltext_vtab *)pVTab;
-  int rc;
-
-  FTSTRACE(("FTS3 Destroy %p\n", pVTab));
-  rc = sql_exec(v->db, v->zDb, v->zName,
-                "drop table if exists %_content;"
-                "drop table if exists %_segments;"
-                "drop table if exists %_segdir;"
-                );
-  if( rc!=SQLITE_OK ) return rc;
-
-  fulltext_vtab_destroy((fulltext_vtab *)pVTab);
-  return SQLITE_OK;
-}
-
-static int fulltextOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor){
-  fulltext_cursor *c;
-
-  c = (fulltext_cursor *) sqlite3_malloc(sizeof(fulltext_cursor));
-  if( c ){
-    memset(c, 0, sizeof(fulltext_cursor));
-    /* sqlite will initialize c->base */
-    *ppCursor = &c->base;
-    FTSTRACE(("FTS3 Open %p: %p\n", pVTab, c));
-    return SQLITE_OK;
+/*
+** Free the Fts3SegReaderArray objects associated with each token in the
+** expression pExpr. In other words, this function frees the resources
+** allocated by fts3ExprAllocateSegReaders().
+*/
+static void fts3ExprFreeSegReaders(Fts3Expr *pExpr){
+  if( pExpr ){
+    Fts3Phrase *pPhrase = pExpr->pPhrase;
+    if( pPhrase ){
+      int kk;
+      for(kk=0; kk<pPhrase->nToken; kk++){
+        fts3SegReaderCursorFree(pPhrase->aToken[kk].pSegcsr);
+        pPhrase->aToken[kk].pSegcsr = 0;
+      }
+    }
+    fts3ExprFreeSegReaders(pExpr->pLeft);
+    fts3ExprFreeSegReaders(pExpr->pRight);
+  }
+}
+
+/*
+** Return the sum of the costs of all tokens in the expression pExpr. This
+** function must be called after Fts3SegReaderArrays have been allocated
+** for all tokens using fts3ExprAllocateSegReaders().
+*/
+static int fts3ExprCost(Fts3Expr *pExpr){
+  int nCost;                      /* Return value */
+  if( pExpr->eType==FTSQUERY_PHRASE ){
+    Fts3Phrase *pPhrase = pExpr->pPhrase;
+    int ii;
+    nCost = 0;
+    for(ii=0; ii<pPhrase->nToken; ii++){
+      Fts3SegReaderCursor *pSegcsr = pPhrase->aToken[ii].pSegcsr;
+      if( pSegcsr ) nCost += pSegcsr->nCost;
+    }
   }else{
-    return SQLITE_NOMEM;
-  }
-}
-
-/* Free all of the dynamically allocated memory held by the
-** Snippet
-*/
-static void snippetClear(Snippet *p){
-  sqlite3_free(p->aMatch);
-  sqlite3_free(p->zOffset);
-  sqlite3_free(p->zSnippet);
-  CLEAR(p);
-}
-
-/*
-** Append a single entry to the p->aMatch[] log.
-*/
-static void snippetAppendMatch(
-  Snippet *p,               /* Append the entry to this snippet */
-  int iCol, int iTerm,      /* The column and query term */
-  int iToken,               /* Matching token in document */
-  int iStart, int nByte     /* Offset and size of the match */
-){
-  int i;
-  struct snippetMatch *pMatch;
-  if( p->nMatch+1>=p->nAlloc ){
-    p->nAlloc = p->nAlloc*2 + 10;
-    p->aMatch = sqlite3_realloc(p->aMatch, p->nAlloc*sizeof(p->aMatch[0]) );
-    if( p->aMatch==0 ){
-      p->nMatch = 0;
-      p->nAlloc = 0;
-      return;
-    }
-  }
-  i = p->nMatch++;
-  pMatch = &p->aMatch[i];
-  pMatch->iCol = iCol;
-  pMatch->iTerm = iTerm;
-  pMatch->iToken = iToken;
-  pMatch->iStart = iStart;
-  pMatch->nByte = nByte;
-}
-
-/*
-** Sizing information for the circular buffer used in snippetOffsetsOfColumn()
-*/
-#define FTS3_ROTOR_SZ   (32)
-#define FTS3_ROTOR_MASK (FTS3_ROTOR_SZ-1)
-
-/*
-** Function to iterate through the tokens of a compiled expression.
-**
-** Except, skip all tokens on the right-hand side of a NOT operator.
-** This function is used to find tokens as part of snippet and offset
-** generation and we do nt want snippets and offsets to report matches
-** for tokens on the RHS of a NOT.
-*/
-static int fts3NextExprToken(Fts3Expr **ppExpr, int *piToken){
-  Fts3Expr *p = *ppExpr;
-  int iToken = *piToken;
-  if( iToken<0 ){
-    /* In this case the expression p is the root of an expression tree.
-    ** Move to the first token in the expression tree.
-    */
-    while( p->pLeft ){
-      p = p->pLeft;
-    }
-    iToken = 0;
+    nCost = fts3ExprCost(pExpr->pLeft) + fts3ExprCost(pExpr->pRight);
+  }
+  return nCost;
+}
+
+/*
+** The following is a helper function (and type) for fts3EvalExpr(). It
+** must be called after Fts3SegReaders have been allocated for every token
+** in the expression. See the context it is called from in fts3EvalExpr()
+** for further explanation.
+*/
+typedef struct ExprAndCost ExprAndCost;
+struct ExprAndCost {
+  Fts3Expr *pExpr;
+  int nCost;
+};
+static void fts3ExprAssignCosts(
+  Fts3Expr *pExpr,                /* Expression to create seg-readers for */
+  ExprAndCost **ppExprCost        /* OUT: Write to *ppExprCost */
+){
+  if( pExpr->eType==FTSQUERY_AND ){
+    fts3ExprAssignCosts(pExpr->pLeft, ppExprCost);
+    fts3ExprAssignCosts(pExpr->pRight, ppExprCost);
   }else{
-    assert(p && p->eType==FTSQUERY_PHRASE );
-    if( iToken<(p->pPhrase->nToken-1) ){
-      iToken++;
-    }else{
-      iToken = 0;
-      while( p->pParent && p->pParent->pLeft!=p ){
-        assert( p->pParent->pRight==p );
-        p = p->pParent;
-      }
-      p = p->pParent;
-      if( p ){
-        assert( p->pRight!=0 );
-        p = p->pRight;
-        while( p->pLeft ){
-          p = p->pLeft;
-        }
-      }
-    }
-  }
-
-  *ppExpr = p;
-  *piToken = iToken;
-  return p?1:0;
-}
-
-/*
-** Return TRUE if the expression node pExpr is located beneath the
-** RHS of a NOT operator.
-*/
-static int fts3ExprBeneathNot(Fts3Expr *p){
-  Fts3Expr *pParent;
-  while( p ){
-    pParent = p->pParent;
-    if( pParent && pParent->eType==FTSQUERY_NOT && pParent->pRight==p ){
-      return 1;
-    }
-    p = pParent;
-  }
-  return 0;
-}
-
-/*
-** Add entries to pSnippet->aMatch[] for every match that occurs against
-** document zDoc[0..nDoc-1] which is stored in column iColumn.
-*/
-static void snippetOffsetsOfColumn(
-  fulltext_cursor *pCur,         /* The fulltest search cursor */
-  Snippet *pSnippet,             /* The Snippet object to be filled in */
-  int iColumn,                   /* Index of fulltext table column */
-  const char *zDoc,              /* Text of the fulltext table column */
-  int nDoc                       /* Length of zDoc in bytes */
-){
-  const sqlite3_tokenizer_module *pTModule;  /* The tokenizer module */
-  sqlite3_tokenizer *pTokenizer;             /* The specific tokenizer */
-  sqlite3_tokenizer_cursor *pTCursor;        /* Tokenizer cursor */
-  fulltext_vtab *pVtab;                /* The full text index */
-  int nColumn;                         /* Number of columns in the index */
-  int i, j;                            /* Loop counters */
-  int rc;                              /* Return code */
-  unsigned int match, prevMatch;       /* Phrase search bitmasks */
-  const char *zToken;                  /* Next token from the tokenizer */
-  int nToken;                          /* Size of zToken */
-  int iBegin, iEnd, iPos;              /* Offsets of beginning and end */
-
-  /* The following variables keep a circular buffer of the last
-  ** few tokens */
-  unsigned int iRotor = 0;             /* Index of current token */
-  int iRotorBegin[FTS3_ROTOR_SZ];      /* Beginning offset of token */
-  int iRotorLen[FTS3_ROTOR_SZ];        /* Length of token */
-
-  pVtab = cursor_vtab(pCur);
-  nColumn = pVtab->nColumn;
-  pTokenizer = pVtab->pTokenizer;
-  pTModule = pTokenizer->pModule;
-  rc = pTModule->xOpen(pTokenizer, zDoc, nDoc, &pTCursor);
-  if( rc ) return;
-  pTCursor->pTokenizer = pTokenizer;
-
-  prevMatch = 0;
-  while( !pTModule->xNext(pTCursor, &zToken, &nToken, &iBegin, &iEnd, &iPos) ){
-    Fts3Expr *pIter = pCur->pExpr;
-    int iIter = -1;
-    iRotorBegin[iRotor&FTS3_ROTOR_MASK] = iBegin;
-    iRotorLen[iRotor&FTS3_ROTOR_MASK] = iEnd-iBegin;
-    match = 0;
-    for(i=0; i<(FTS3_ROTOR_SZ-1) && fts3NextExprToken(&pIter, &iIter); i++){
-      int nPhrase;                    /* Number of tokens in current phrase */
-      struct PhraseToken *pToken;     /* Current token */
-      int iCol;                       /* Column index */
-
-      if( fts3ExprBeneathNot(pIter) ) continue;
-      nPhrase = pIter->pPhrase->nToken;
-      pToken = &pIter->pPhrase->aToken[iIter];
-      iCol = pIter->pPhrase->iColumn;
-      if( iCol>=0 && iCol<nColumn && iCol!=iColumn ) continue;
-      if( pToken->n>nToken ) continue;
-      if( !pToken->isPrefix && pToken->n<nToken ) continue;
-      assert( pToken->n<=nToken );
-      if( memcmp(pToken->z, zToken, pToken->n) ) continue;
-      if( iIter>0 && (prevMatch & (1<<i))==0 ) continue;
-      match |= 1<<i;
-      if( i==(FTS3_ROTOR_SZ-2) || nPhrase==iIter+1 ){
-        for(j=nPhrase-1; j>=0; j--){
-          int k = (iRotor-j) & FTS3_ROTOR_MASK;
-          snippetAppendMatch(pSnippet, iColumn, i-j, iPos-j,
-                iRotorBegin[k], iRotorLen[k]);
-        }
-      }
-    }
-    prevMatch = match<<1;
-    iRotor++;
-  }
-  pTModule->xClose(pTCursor);  
-}
-
-/*
-** Remove entries from the pSnippet structure to account for the NEAR
-** operator. When this is called, pSnippet contains the list of token 
-** offsets produced by treating all NEAR operators as AND operators.
-** This function removes any entries that should not be present after
-** accounting for the NEAR restriction. For example, if the queried
-** document is:
-**
-**     "A B C D E A"
-**
-** and the query is:
-** 
-**     A NEAR/0 E
-**
-** then when this function is called the Snippet contains token offsets
-** 0, 4 and 5. This function removes the "0" entry (because the first A
-** is not near enough to an E).
-**
-** When this function is called, the value pointed to by parameter piLeft is
-** the integer id of the left-most token in the expression tree headed by
-** pExpr. This function increments *piLeft by the total number of tokens
-** in the expression tree headed by pExpr.
-**
-** Return 1 if any trimming occurs.  Return 0 if no trimming is required.
-*/
-static int trimSnippetOffsets(
-  Fts3Expr *pExpr,      /* The search expression */
-  Snippet *pSnippet,    /* The set of snippet offsets to be trimmed */
-  int *piLeft           /* Index of left-most token in pExpr */
-){
+    (*ppExprCost)->pExpr = pExpr;
+    (*ppExprCost)->nCost = fts3ExprCost(pExpr);
+    (*ppExprCost)++;
+  }
+}
+
+/*
+** Evaluate the full-text expression pExpr against FTS3 table pTab. Store
+** the resulting doclist in *paOut and *pnOut. This routine mallocs for
+** the space needed to store the output. The caller is responsible for
+** freeing the space when it has finished.
+**
+** This function is called in two distinct contexts:
+**
+**   * From within the virtual table xFilter() method. In this case, the
+**     output doclist contains entries for all rows in the table, based on
+**     data read from the full-text index.
+**
+**     In this case, if the query expression contains one or more tokens that 
+**     are very common, then the returned doclist may contain a superset of 
+**     the documents that actually match the expression.
+**
+**   * From within the virtual table xNext() method. This call is only made
+**     if the call from within xFilter() found that there were very common 
+**     tokens in the query expression and did return a superset of the 
+**     matching documents. In this case the returned doclist contains only
+**     entries that correspond to the current row of the table. Instead of
+**     reading the data for each token from the full-text index, the data is
+**     already available in-memory in the Fts3PhraseToken.pDeferred structures.
+**     See fts3EvalDeferred() for how it gets there.
+**
+** In the first case above, Fts3Cursor.doDeferred==0. In the second (if it is
+** required) Fts3Cursor.doDeferred==1.
+**
+** If the SQLite invokes the snippet(), offsets() or matchinfo() function
+** as part of a SELECT on an FTS3 table, this function is called on each
+** individual phrase expression in the query. If there were very common tokens
+** found in the xFilter() call, then this function is called once for phrase
+** for each row visited, and the returned doclist contains entries for the
+** current row only. Otherwise, if there were no very common tokens, then this
+** function is called once only for each phrase in the query and the returned
+** doclist contains entries for all rows of the table.
+**
+** Fts3Cursor.doDeferred==1 when this function is called on phrases as a
+** result of a snippet(), offsets() or matchinfo() invocation.
+*/
+static int fts3EvalExpr(
+  Fts3Cursor *p,                  /* Virtual table cursor handle */
+  Fts3Expr *pExpr,                /* Parsed fts3 expression */
+  char **paOut,                   /* OUT: Pointer to malloc'd result buffer */
+  int *pnOut,                     /* OUT: Size of buffer at *paOut */
+  int isReqPos                    /* Require positions in output buffer */
+){
+  int rc = SQLITE_OK;             /* Return code */
+
+  /* Zero the output parameters. */
+  *paOut = 0;
+  *pnOut = 0;
+
   if( pExpr ){
-    if( trimSnippetOffsets(pExpr->pLeft, pSnippet, piLeft) ){
-      return 1;
-    }
-
-    switch( pExpr->eType ){
-      case FTSQUERY_PHRASE:
-        *piLeft += pExpr->pPhrase->nToken;
-        break;
-      case FTSQUERY_NEAR: {
-        /* The right-hand-side of a NEAR operator is always a phrase. The
-        ** left-hand-side is either a phrase or an expression tree that is 
-        ** itself headed by a NEAR operator. The following initializations
-        ** set local variable iLeft to the token number of the left-most
-        ** token in the right-hand phrase, and iRight to the right most
-        ** token in the same phrase. For example, if we had:
-        **
-        **     <col> MATCH '"abc def" NEAR/2 "ghi jkl"'
-        **
-        ** then iLeft will be set to 2 (token number of ghi) and nToken will
-        ** be set to 4.
-        */
-        Fts3Expr *pLeft = pExpr->pLeft;
-        Fts3Expr *pRight = pExpr->pRight;
-        int iLeft = *piLeft;
-        int nNear = pExpr->nNear;
-        int nToken = pRight->pPhrase->nToken;
-        int jj, ii;
-        if( pLeft->eType==FTSQUERY_NEAR ){
-          pLeft = pLeft->pRight;
-        }
-        assert( pRight->eType==FTSQUERY_PHRASE );
-        assert( pLeft->eType==FTSQUERY_PHRASE );
-        nToken += pLeft->pPhrase->nToken;
-
-        for(ii=0; ii<pSnippet->nMatch; ii++){
-          struct snippetMatch *p = &pSnippet->aMatch[ii];
-          if( p->iTerm==iLeft ){
-            int isOk = 0;
-            /* Snippet ii is an occurence of query term iLeft in the document.
-            ** It occurs at position (p->iToken) of the document. We now
-            ** search for an instance of token (iLeft-1) somewhere in the 
-            ** range (p->iToken - nNear)...(p->iToken + nNear + nToken) within 
-            ** the set of snippetMatch structures. If one is found, proceed. 
-            ** If one cannot be found, then remove snippets ii..(ii+N-1) 
-            ** from the matching snippets, where N is the number of tokens 
-            ** in phrase pRight->pPhrase.
-            */
-            for(jj=0; isOk==0 && jj<pSnippet->nMatch; jj++){
-              struct snippetMatch *p2 = &pSnippet->aMatch[jj];
-              if( p2->iTerm==(iLeft-1) ){
-                if( p2->iToken>=(p->iToken-nNear-1) 
-                 && p2->iToken<(p->iToken+nNear+nToken) 
-                ){
-                  isOk = 1;
-                }
-              }
-            }
-            if( !isOk ){
-              int kk;
-              for(kk=0; kk<pRight->pPhrase->nToken; kk++){
-                pSnippet->aMatch[kk+ii].iTerm = -2;
-              }
-              return 1;
+    assert( pExpr->eType==FTSQUERY_NEAR   || pExpr->eType==FTSQUERY_OR     
+         || pExpr->eType==FTSQUERY_AND    || pExpr->eType==FTSQUERY_NOT
+         || pExpr->eType==FTSQUERY_PHRASE
+    );
+    assert( pExpr->eType==FTSQUERY_PHRASE || isReqPos==0 );
+
+    if( pExpr->eType==FTSQUERY_PHRASE ){
+      rc = fts3PhraseSelect(p, pExpr->pPhrase,
+          isReqPos || (pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR),
+          paOut, pnOut
+      );
+      fts3ExprFreeSegReaders(pExpr);
+    }else if( p->eEvalmode==FTS3_EVAL_FILTER && pExpr->eType==FTSQUERY_AND ){
+      ExprAndCost *aExpr = 0;     /* Array of AND'd expressions and costs */
+      int nExpr = 0;              /* Size of aExpr[] */
+      char *aRet = 0;             /* Doclist to return to caller */
+      int nRet = 0;               /* Length of aRet[] in bytes */
+      int nDoc = 0x7FFFFFFF;
+
+      assert( !isReqPos );
+
+      rc = fts3ExprAllocateSegReaders(p, pExpr, &nExpr);
+      if( rc==SQLITE_OK ){
+        assert( nExpr>1 );
+        aExpr = sqlite3_malloc(sizeof(ExprAndCost) * nExpr);
+        if( !aExpr ) rc = SQLITE_NOMEM;
+      }
+      if( rc==SQLITE_OK ){
+        int ii;                   /* Used to iterate through expressions */
+
+        fts3ExprAssignCosts(pExpr, &aExpr);
+        aExpr -= nExpr;
+        for(ii=0; ii<nExpr; ii++){
+          char *aNew;
+          int nNew;
+          int jj;
+          ExprAndCost *pBest = 0;
+  
+          for(jj=0; jj<nExpr; jj++){
+            ExprAndCost *pCand = &aExpr[jj];
+            if( pCand->pExpr && (pBest==0 || pCand->nCost<pBest->nCost) ){
+              pBest = pCand;
             }
           }
-          if( p->iTerm==(iLeft-1) ){
-            int isOk = 0;
-            for(jj=0; isOk==0 && jj<pSnippet->nMatch; jj++){
-              struct snippetMatch *p2 = &pSnippet->aMatch[jj];
-              if( p2->iTerm==iLeft ){
-                if( p2->iToken<=(p->iToken+nNear+1) 
-                 && p2->iToken>(p->iToken-nNear-nToken) 
-                ){
-                  isOk = 1;
-                }
-              }
-            }
-            if( !isOk ){
-              int kk;
-              for(kk=0; kk<pLeft->pPhrase->nToken; kk++){
-                pSnippet->aMatch[ii-kk].iTerm = -2;
-              }
-              return 1;
+  
+          if( pBest->nCost>nDoc ){
+            rc = fts3DeferExpression(p, p->pExpr);
+            break;
+          }else{
+            rc = fts3EvalExpr(p, pBest->pExpr, &aNew, &nNew, 0);
+            if( rc!=SQLITE_OK ) break;
+            pBest->pExpr = 0;
+            if( ii==0 ){
+              aRet = aNew;
+              nRet = nNew;
+              nDoc = fts3DoclistCountDocids(0, aRet, nRet);
+            }else{
+              fts3DoclistMerge(
+                  MERGE_AND, 0, 0, aRet, &nRet, aRet, nRet, aNew, nNew, &nDoc
+              );
+              sqlite3_free(aNew);
             }
           }
         }
-        break;
-      }
-    }
-
-    if( trimSnippetOffsets(pExpr->pRight, pSnippet, piLeft) ){
-      return 1;
-    }
-  }
-  return 0;
-}
-
-/*
-** Compute all offsets for the current row of the query.  
-** If the offsets have already been computed, this routine is a no-op.
-*/
-static void snippetAllOffsets(fulltext_cursor *p){
-  int nColumn;
-  int iColumn, i;
-  int iFirst, iLast;
-  int iTerm = 0;
-  fulltext_vtab *pFts = cursor_vtab(p);
-
-  if( p->snippet.nMatch || p->pExpr==0 ){
-    return;
-  }
-  nColumn = pFts->nColumn;
-  iColumn = (p->iCursorType - QUERY_FULLTEXT);
-  if( iColumn<0 || iColumn>=nColumn ){
-    /* Look for matches over all columns of the full-text index */
-    iFirst = 0;
-    iLast = nColumn-1;
-  }else{
-    /* Look for matches in the iColumn-th column of the index only */
-    iFirst = iColumn;
-    iLast = iColumn;
-  }
-  for(i=iFirst; i<=iLast; i++){
-    const char *zDoc;
-    int nDoc;
-    zDoc = (const char*)sqlite3_column_text(p->pStmt, i+1);
-    nDoc = sqlite3_column_bytes(p->pStmt, i+1);
-    snippetOffsetsOfColumn(p, &p->snippet, i, zDoc, nDoc);
-  }
-
-  while( trimSnippetOffsets(p->pExpr, &p->snippet, &iTerm) ){
-    iTerm = 0;
-  }
-}
-
-/*
-** Convert the information in the aMatch[] array of the snippet
-** into the string zOffset[0..nOffset-1]. This string is used as
-** the return of the SQL offsets() function.
-*/
-static void snippetOffsetText(Snippet *p){
-  int i;
-  int cnt = 0;
-  StringBuffer sb;
-  char zBuf[200];
-  if( p->zOffset ) return;
-  initStringBuffer(&sb);
-  for(i=0; i<p->nMatch; i++){
-    struct snippetMatch *pMatch = &p->aMatch[i];
-    if( pMatch->iTerm>=0 ){
-      /* If snippetMatch.iTerm is less than 0, then the match was 
-      ** discarded as part of processing the NEAR operator (see the 
-      ** trimSnippetOffsetsForNear() function for details). Ignore 
-      ** it in this case
-      */
-      zBuf[0] = ' ';
-      sqlite3_snprintf(sizeof(zBuf)-1, &zBuf[cnt>0], "%d %d %d %d",
-          pMatch->iCol, pMatch->iTerm, pMatch->iStart, pMatch->nByte);
-      append(&sb, zBuf);
-      cnt++;
-    }
-  }
-  p->zOffset = stringBufferData(&sb);
-  p->nOffset = stringBufferLength(&sb);
-}
-
-/*
-** zDoc[0..nDoc-1] is phrase of text.  aMatch[0..nMatch-1] are a set
-** of matching words some of which might be in zDoc.  zDoc is column
-** number iCol.
-**
-** iBreak is suggested spot in zDoc where we could begin or end an
-** excerpt.  Return a value similar to iBreak but possibly adjusted
-** to be a little left or right so that the break point is better.
-*/
-static int wordBoundary(
-  int iBreak,                   /* The suggested break point */
-  const char *zDoc,             /* Document text */
-  int nDoc,                     /* Number of bytes in zDoc[] */
-  struct snippetMatch *aMatch,  /* Matching words */
-  int nMatch,                   /* Number of entries in aMatch[] */
-  int iCol                      /* The column number for zDoc[] */
-){
-  int i;
-  if( iBreak<=10 ){
-    return 0;
-  }
-  if( iBreak>=nDoc-10 ){
-    return nDoc;
-  }
-  for(i=0; i<nMatch && aMatch[i].iCol<iCol; i++){}
-  while( i<nMatch && aMatch[i].iStart+aMatch[i].nByte<iBreak ){ i++; }
-  if( i<nMatch ){
-    if( aMatch[i].iStart<iBreak+10 ){
-      return aMatch[i].iStart;
-    }
-    if( i>0 && aMatch[i-1].iStart+aMatch[i-1].nByte>=iBreak ){
-      return aMatch[i-1].iStart;
-    }
-  }
-  for(i=1; i<=10; i++){
-    if( safe_isspace(zDoc[iBreak-i]) ){
-      return iBreak - i + 1;
-    }
-    if( safe_isspace(zDoc[iBreak+i]) ){
-      return iBreak + i + 1;
-    }
-  }
-  return iBreak;
-}
-
-
-
-/*
-** Allowed values for Snippet.aMatch[].snStatus
-*/
-#define SNIPPET_IGNORE  0   /* It is ok to omit this match from the snippet */
-#define SNIPPET_DESIRED 1   /* We want to include this match in the snippet */
-
-/*
-** Generate the text of a snippet.
-*/
-static void snippetText(
-  fulltext_cursor *pCursor,   /* The cursor we need the snippet for */
-  const char *zStartMark,     /* Markup to appear before each match */
-  const char *zEndMark,       /* Markup to appear after each match */
-  const char *zEllipsis       /* Ellipsis mark */
-){
-  int i, j;
-  struct snippetMatch *aMatch;
-  int nMatch;
-  int nDesired;
-  StringBuffer sb;
-  int tailCol;
-  int tailOffset;
-  int iCol;
-  int nDoc;
-  const char *zDoc;
-  int iStart, iEnd;
-  int tailEllipsis = 0;
-  int iMatch;
-  
-
-  sqlite3_free(pCursor->snippet.zSnippet);
-  pCursor->snippet.zSnippet = 0;
-  aMatch = pCursor->snippet.aMatch;
-  nMatch = pCursor->snippet.nMatch;
-  initStringBuffer(&sb);
-
-  for(i=0; i<nMatch; i++){
-    aMatch[i].snStatus = SNIPPET_IGNORE;
-  }
-  nDesired = 0;
-  for(i=0; i<FTS3_ROTOR_SZ; i++){
-    for(j=0; j<nMatch; j++){
-      if( aMatch[j].iTerm==i ){
-        aMatch[j].snStatus = SNIPPET_DESIRED;
-        nDesired++;
-        break;
-      }
-    }
-  }
-
-  iMatch = 0;
-  tailCol = -1;
-  tailOffset = 0;
-  for(i=0; i<nMatch && nDesired>0; i++){
-    if( aMatch[i].snStatus!=SNIPPET_DESIRED ) continue;
-    nDesired--;
-    iCol = aMatch[i].iCol;
-    zDoc = (const char*)sqlite3_column_text(pCursor->pStmt, iCol+1);
-    nDoc = sqlite3_column_bytes(pCursor->pStmt, iCol+1);
-    iStart = aMatch[i].iStart - 40;
-    iStart = wordBoundary(iStart, zDoc, nDoc, aMatch, nMatch, iCol);
-    if( iStart<=10 ){
-      iStart = 0;
-    }
-    if( iCol==tailCol && iStart<=tailOffset+20 ){
-      iStart = tailOffset;
-    }
-    if( (iCol!=tailCol && tailCol>=0) || iStart!=tailOffset ){
-      trimWhiteSpace(&sb);
-      appendWhiteSpace(&sb);
-      append(&sb, zEllipsis);
-      appendWhiteSpace(&sb);
-    }
-    iEnd = aMatch[i].iStart + aMatch[i].nByte + 40;
-    iEnd = wordBoundary(iEnd, zDoc, nDoc, aMatch, nMatch, iCol);
-    if( iEnd>=nDoc-10 ){
-      iEnd = nDoc;
-      tailEllipsis = 0;
+      }
+
+      if( rc==SQLITE_OK ){
+        *paOut = aRet;
+        *pnOut = nRet;
+      }else{
+        assert( *paOut==0 );
+        sqlite3_free(aRet);
+      }
+      sqlite3_free(aExpr);
+      fts3ExprFreeSegReaders(pExpr);
+
     }else{
-      tailEllipsis = 1;
-    }
-    while( iMatch<nMatch && aMatch[iMatch].iCol<iCol ){ iMatch++; }
-    while( iStart<iEnd ){
-      while( iMatch<nMatch && aMatch[iMatch].iStart<iStart
-             && aMatch[iMatch].iCol<=iCol ){
-        iMatch++;
-      }
-      if( iMatch<nMatch && aMatch[iMatch].iStart<iEnd
-             && aMatch[iMatch].iCol==iCol ){
-        nappend(&sb, &zDoc[iStart], aMatch[iMatch].iStart - iStart);
-        iStart = aMatch[iMatch].iStart;
-        append(&sb, zStartMark);
-        nappend(&sb, &zDoc[iStart], aMatch[iMatch].nByte);
-        append(&sb, zEndMark);
-        iStart += aMatch[iMatch].nByte;
-        for(j=iMatch+1; j<nMatch; j++){
-          if( aMatch[j].iTerm==aMatch[iMatch].iTerm
-              && aMatch[j].snStatus==SNIPPET_DESIRED ){
-            nDesired--;
-            aMatch[j].snStatus = SNIPPET_IGNORE;
-          }
-        }
-      }else{
-        nappend(&sb, &zDoc[iStart], iEnd - iStart);
-        iStart = iEnd;
-      }
-    }
-    tailCol = iCol;
-    tailOffset = iEnd;
-  }
-  trimWhiteSpace(&sb);
-  if( tailEllipsis ){
-    appendWhiteSpace(&sb);
-    append(&sb, zEllipsis);
-  }
-  pCursor->snippet.zSnippet = stringBufferData(&sb);
-  pCursor->snippet.nSnippet = stringBufferLength(&sb);
-}
-
-
-/*
-** Close the cursor.  For additional information see the documentation
-** on the xClose method of the virtual table interface.
-*/
-static int fulltextClose(sqlite3_vtab_cursor *pCursor){
-  fulltext_cursor *c = (fulltext_cursor *) pCursor;
-  FTSTRACE(("FTS3 Close %p\n", c));
-  sqlite3_finalize(c->pStmt);
-  sqlite3Fts3ExprFree(c->pExpr);
-  snippetClear(&c->snippet);
-  if( c->result.nData!=0 ){
-    dlrDestroy(&c->reader);
-  }
-  dataBufferDestroy(&c->result);
-  sqlite3_free(c);
-  return SQLITE_OK;
-}
-
-static int fulltextNext(sqlite3_vtab_cursor *pCursor){
-  fulltext_cursor *c = (fulltext_cursor *) pCursor;
-  int rc;
-
-  FTSTRACE(("FTS3 Next %p\n", pCursor));
-  snippetClear(&c->snippet);
-  if( c->iCursorType < QUERY_FULLTEXT ){
-    /* TODO(shess) Handle SQLITE_SCHEMA AND SQLITE_BUSY. */
-    rc = sqlite3_step(c->pStmt);
-    switch( rc ){
-      case SQLITE_ROW:
-        c->eof = 0;
-        return SQLITE_OK;
-      case SQLITE_DONE:
-        c->eof = 1;
-        return SQLITE_OK;
-      default:
-        c->eof = 1;
-        return rc;
-    }
-  } else {  /* full-text query */
-    rc = sqlite3_reset(c->pStmt);
-    if( rc!=SQLITE_OK ) return rc;
-
-    if( c->result.nData==0 || dlrAtEnd(&c->reader) ){
-      c->eof = 1;
-      return SQLITE_OK;
-    }
-    rc = sqlite3_bind_int64(c->pStmt, 1, dlrDocid(&c->reader));
-    if( rc!=SQLITE_OK ) return rc;
-    rc = dlrStep(&c->reader);
-    if( rc!=SQLITE_OK ) return rc;
-    /* TODO(shess) Handle SQLITE_SCHEMA AND SQLITE_BUSY. */
-    rc = sqlite3_step(c->pStmt);
-    if( rc==SQLITE_ROW ){   /* the case we expect */
-      c->eof = 0;
-      return SQLITE_OK;
-    }
-    /* Corrupt if the index refers to missing document. */
-    if( rc==SQLITE_DONE ) return SQLITE_CORRUPT_BKPT;
-
-    return rc;
-  }
-}
-
-
-/* TODO(shess) If we pushed LeafReader to the top of the file, or to
-** another file, term_select() could be pushed above
-** docListOfTerm().
-*/
-static int termSelect(fulltext_vtab *v, int iColumn,
-                      const char *pTerm, int nTerm, int isPrefix,
-                      DocListType iType, DataBuffer *out);
-
-/* 
-** Return a DocList corresponding to the phrase *pPhrase.
-**
-** The resulting DL_DOCIDS doclist is stored in pResult, which is
-** overwritten.
-*/
-static int docListOfPhrase(
-  fulltext_vtab *pTab,   /* The full text index */
-  Fts3Phrase *pPhrase,   /* Phrase to return a doclist corresponding to */
-  DocListType eListType, /* Either DL_DOCIDS or DL_POSITIONS */
-  DataBuffer *pResult    /* Write the result here */
-){
-  int ii;
-  int rc = SQLITE_OK;
-  int iCol = pPhrase->iColumn;
-  DocListType eType = eListType;
-  assert( eType==DL_POSITIONS || eType==DL_DOCIDS );
-  if( pPhrase->nToken>1 ){
-    eType = DL_POSITIONS;
-  }
-
-  /* This code should never be called with buffered updates. */
-  assert( pTab->nPendingData<0 );
-
-  for(ii=0; rc==SQLITE_OK && ii<pPhrase->nToken; ii++){
-    DataBuffer tmp;
-    struct PhraseToken *p = &pPhrase->aToken[ii];
-    rc = termSelect(pTab, iCol, p->z, p->n, p->isPrefix, eType, &tmp);
-    if( rc==SQLITE_OK ){
-      if( ii==0 ){
-        *pResult = tmp;
-      }else{
-        DataBuffer res = *pResult;
-        dataBufferInit(pResult, 0);
-        if( ii==(pPhrase->nToken-1) ){
-          eType = eListType;
-        }
-        rc = docListPhraseMerge(
-          res.pData, res.nData, tmp.pData, tmp.nData, 0, 0, eType, pResult
-        );
-        dataBufferDestroy(&res);
-        dataBufferDestroy(&tmp);
-        if( rc!= SQLITE_OK ) return rc;
-      }
-    }
-  }
-
-  return rc;
-}
-
-/*
-** Evaluate the full-text expression pExpr against fts3 table pTab. Write
-** the results into pRes.
-*/
-static int evalFts3Expr(
-  fulltext_vtab *pTab,           /* Fts3 Virtual table object */
-  Fts3Expr *pExpr,               /* Parsed fts3 expression */
-  DataBuffer *pRes               /* OUT: Write results of the expression here */
-){
-  int rc = SQLITE_OK;
-
-  /* Initialize the output buffer. If this is an empty query (pExpr==0), 
-  ** this is all that needs to be done. Empty queries produce empty 
-  ** result sets.
-  */
-  dataBufferInit(pRes, 0);
-
-  if( pExpr ){
-    if( pExpr->eType==FTSQUERY_PHRASE ){
-      DocListType eType = DL_DOCIDS;
-      if( pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR ){
-        eType = DL_POSITIONS;
-      }
-      rc = docListOfPhrase(pTab, pExpr->pPhrase, eType, pRes);
-    }else{
-      DataBuffer lhs;
-      DataBuffer rhs;
-
-      dataBufferInit(&rhs, 0);
-      if( SQLITE_OK==(rc = evalFts3Expr(pTab, pExpr->pLeft, &lhs)) 
-       && SQLITE_OK==(rc = evalFts3Expr(pTab, pExpr->pRight, &rhs)) 
+      char *aLeft;
+      char *aRight;
+      int nLeft;
+      int nRight;
+
+      assert( pExpr->eType==FTSQUERY_NEAR 
+           || pExpr->eType==FTSQUERY_OR
+           || pExpr->eType==FTSQUERY_NOT
+           || (pExpr->eType==FTSQUERY_AND && p->eEvalmode==FTS3_EVAL_NEXT)
+      );
+
+      if( 0==(rc = fts3EvalExpr(p, pExpr->pRight, &aRight, &nRight, isReqPos))
+       && 0==(rc = fts3EvalExpr(p, pExpr->pLeft, &aLeft, &nLeft, isReqPos))
       ){
         switch( pExpr->eType ){
           case FTSQUERY_NEAR: {
-            int nToken;
             Fts3Expr *pLeft;
-            DocListType eType = DL_DOCIDS;
+            Fts3Expr *pRight;
+            int mergetype = MERGE_NEAR;
             if( pExpr->pParent && pExpr->pParent->eType==FTSQUERY_NEAR ){
-              eType = DL_POSITIONS;
+              mergetype = MERGE_POS_NEAR;
             }
             pLeft = pExpr->pLeft;
             while( pLeft->eType==FTSQUERY_NEAR ){ 
               pLeft=pLeft->pRight;
             }
-            assert( pExpr->pRight->eType==FTSQUERY_PHRASE );
+            pRight = pExpr->pRight;
+            assert( pRight->eType==FTSQUERY_PHRASE );
             assert( pLeft->eType==FTSQUERY_PHRASE );
-            nToken = pLeft->pPhrase->nToken + pExpr->pRight->pPhrase->nToken;
-            rc = docListPhraseMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData, 
-                pExpr->nNear+1, nToken, eType, pRes
+
+            rc = fts3NearMerge(mergetype, pExpr->nNear, 
+                pLeft->pPhrase->nToken, aLeft, nLeft,
+                pRight->pPhrase->nToken, aRight, nRight,
+                paOut, pnOut
             );
+            sqlite3_free(aLeft);
             break;
           }
-          case FTSQUERY_NOT: {
-            rc = docListExceptMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData,pRes);
+
+          case FTSQUERY_OR: {
+            /* Allocate a buffer for the output. The maximum size is the
+            ** sum of the sizes of the two input buffers. The +1 term is
+            ** so that a buffer of zero bytes is never allocated - this can
+            ** cause fts3DoclistMerge() to incorrectly return SQLITE_NOMEM.
+            */
+            char *aBuffer = sqlite3_malloc(nRight+nLeft+1);
+            rc = fts3DoclistMerge(MERGE_OR, 0, 0, aBuffer, pnOut,
+                aLeft, nLeft, aRight, nRight, 0
+            );
+            *paOut = aBuffer;
+            sqlite3_free(aLeft);
             break;
           }
-          case FTSQUERY_AND: {
-            rc = docListAndMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData, pRes);
-            break;
-          }
-          case FTSQUERY_OR: {
-            rc = docListOrMerge(lhs.pData, lhs.nData, rhs.pData, rhs.nData, pRes);
+
+          default: {
+            assert( FTSQUERY_NOT==MERGE_NOT && FTSQUERY_AND==MERGE_AND );
+            fts3DoclistMerge(pExpr->eType, 0, 0, aLeft, pnOut,
+                aLeft, nLeft, aRight, nRight, 0
+            );
+            *paOut = aLeft;
             break;
           }
         }
       }
-      dataBufferDestroy(&lhs);
-      dataBufferDestroy(&rhs);
-    }
-  }
-
+      sqlite3_free(aRight);
+    }
+  }
+
+  assert( rc==SQLITE_OK || *paOut==0 );
   return rc;
 }
 
-/* TODO(shess) Refactor the code to remove this forward decl. */
-static int flushPendingTerms(fulltext_vtab *v);
-
-/* Perform a full-text query using the search expression in
-** zInput[0..nInput-1].  Return a list of matching documents
-** in pResult.
-**
-** Queries must match column iColumn.  Or if iColumn>=nColumn
-** they are allowed to match against any column.
-*/
-static int fulltextQuery(
-  fulltext_vtab *v,      /* The full text index */
-  int iColumn,           /* Match against this column by default */
-  const char *zInput,    /* The query string */
-  int nInput,            /* Number of bytes in zInput[] */
-  DataBuffer *pResult,   /* Write the result doclist here */
-  Fts3Expr **ppExpr        /* Put parsed query string here */
-){
-  int rc;
-
-  /* TODO(shess) Instead of flushing pendingTerms, we could query for
-  ** the relevant term and merge the doclist into what we receive from
-  ** the database.  Wait and see if this is a common issue, first.
-  **
-  ** A good reason not to flush is to not generate update-related
-  ** error codes from here.
-  */
-
-  /* Flush any buffered updates before executing the query. */
-  rc = flushPendingTerms(v);
-  if( rc!=SQLITE_OK ){
-    return rc;
-  }
-
-  /* Parse the query passed to the MATCH operator. */
-  rc = sqlite3Fts3ExprParse(v->pTokenizer, 
-      v->azColumn, v->nColumn, iColumn, zInput, nInput, ppExpr
-  );
-  if( rc!=SQLITE_OK ){
-    assert( 0==(*ppExpr) );
-    return rc;
-  }
-
-  return evalFts3Expr(v, *ppExpr, pResult);
+/*
+** This function is called from within xNext() for each row visited by
+** an FTS3 query. If evaluating the FTS3 query expression within xFilter()
+** was able to determine the exact set of matching rows, this function sets
+** *pbRes to true and returns SQLITE_IO immediately.
+**
+** Otherwise, if evaluating the query expression within xFilter() returned a
+** superset of the matching documents instead of an exact set (this happens
+** when the query includes very common tokens and it is deemed too expensive to
+** load their doclists from disk), this function tests if the current row
+** really does match the FTS3 query.
+**
+** If an error occurs, an SQLite error code is returned. Otherwise, SQLITE_OK
+** is returned and *pbRes is set to true if the current row matches the
+** FTS3 query (and should be included in the results returned to SQLite), or
+** false otherwise.
+*/
+static int fts3EvalDeferred(
+  Fts3Cursor *pCsr,               /* FTS3 cursor pointing at row to test */
+  int *pbRes                      /* OUT: Set to true if row is a match */
+){
+  int rc = SQLITE_OK;
+  if( pCsr->pDeferred==0 ){
+    *pbRes = 1;
+  }else{
+    rc = fts3CursorSeek(0, pCsr);
+    if( rc==SQLITE_OK ){
+      sqlite3Fts3FreeDeferredDoclists(pCsr);
+      rc = sqlite3Fts3CacheDeferredDoclists(pCsr);
+    }
+    if( rc==SQLITE_OK ){
+      char *a = 0;
+      int n = 0;
+      rc = fts3EvalExpr(pCsr, pCsr->pExpr, &a, &n, 0);
+      assert( n>=0 );
+      *pbRes = (n>0);
+      sqlite3_free(a);
+    }
+  }
+  return rc;
+}
+
+/*
+** Advance the cursor to the next row in the %_content table that
+** matches the search criteria.  For a MATCH search, this will be
+** the next row that matches. For a full-table scan, this will be
+** simply the next row in the %_content table.  For a docid lookup,
+** this routine simply sets the EOF flag.
+**
+** Return SQLITE_OK if nothing goes wrong.  SQLITE_OK is returned
+** even if we reach end-of-file.  The fts3EofMethod() will be called
+** subsequently to determine whether or not an EOF was hit.
+*/
+static int fts3NextMethod(sqlite3_vtab_cursor *pCursor){
+  int res;
+  int rc = SQLITE_OK;             /* Return code */
+  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
+
+  pCsr->eEvalmode = FTS3_EVAL_NEXT;
+  do {
+    if( pCsr->aDoclist==0 ){
+      if( SQLITE_ROW!=sqlite3_step(pCsr->pStmt) ){
+        pCsr->isEof = 1;
+        rc = sqlite3_reset(pCsr->pStmt);
+        break;
+      }
+      pCsr->iPrevId = sqlite3_column_int64(pCsr->pStmt, 0);
+    }else{
+      if( pCsr->pNextId>=&pCsr->aDoclist[pCsr->nDoclist] ){
+        pCsr->isEof = 1;
+        break;
+      }
+      sqlite3_reset(pCsr->pStmt);
+      fts3GetDeltaVarint(&pCsr->pNextId, &pCsr->iPrevId);
+      pCsr->isRequireSeek = 1;
+      pCsr->isMatchinfoNeeded = 1;
+    }
+  }while( SQLITE_OK==(rc = fts3EvalDeferred(pCsr, &res)) && res==0 );
+
+  return rc;
 }
 
 /*
 ** This is the xFilter interface for the virtual table.  See
 ** the virtual table xFilter method documentation for additional
 ** information.
 **
-** If idxNum==QUERY_GENERIC then do a full table scan against
+** If idxNum==FTS3_FULLSCAN_SEARCH then do a full table scan against
 ** the %_content table.
 **
-** If idxNum==QUERY_DOCID then do a docid lookup for a single entry
+** If idxNum==FTS3_DOCID_SEARCH then do a docid lookup for a single entry
 ** in the %_content table.
 **
-** If idxNum>=QUERY_FULLTEXT then use the full text index.  The
+** If idxNum>=FTS3_FULLTEXT_SEARCH then use the full text index.  The
 ** column on the left-hand side of the MATCH operator is column
-** number idxNum-QUERY_FULLTEXT, 0 indexed.  argv[0] is the right-hand
+** number idxNum-FTS3_FULLTEXT_SEARCH, 0 indexed.  argv[0] is the right-hand
 ** side of the MATCH operator.
 */
-/* TODO(shess) Upgrade the cursor initialization and destruction to
-** account for fulltextFilter() being called multiple times on the
-** same cursor.  The current solution is very fragile.  Apply fix to
-** fts3 as appropriate.
-*/
-static int fulltextFilter(
-  sqlite3_vtab_cursor *pCursor,     /* The cursor used for this query */
-  int idxNum, const char *idxStr,   /* Which indexing scheme to use */
-  int argc, sqlite3_value **argv    /* Arguments for the indexing scheme */
-){
-  fulltext_cursor *c = (fulltext_cursor *) pCursor;
-  fulltext_vtab *v = cursor_vtab(c);
+static int fts3FilterMethod(
+  sqlite3_vtab_cursor *pCursor,   /* The cursor used for this query */
+  int idxNum,                     /* Strategy index */
+  const char *idxStr,             /* Unused */
+  int nVal,                       /* Number of elements in apVal */
+  sqlite3_value **apVal           /* Arguments for the indexing scheme */
+){
+  const char *azSql[] = {
+    "SELECT %s FROM %Q.'%q_content' AS x WHERE docid = ?", /* non-full-scan */
+    "SELECT %s FROM %Q.'%q_content' AS x ",                /* full-scan */
+  };
+  int rc;                         /* Return code */
+  char *zSql;                     /* SQL statement used to access %_content */
+  Fts3Table *p = (Fts3Table *)pCursor->pVtab;
+  Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
+
+  UNUSED_PARAMETER(idxStr);
+  UNUSED_PARAMETER(nVal);
+
+  assert( idxNum>=0 && idxNum<=(FTS3_FULLTEXT_SEARCH+p->nColumn) );
+  assert( nVal==0 || nVal==1 );
+  assert( (nVal==0)==(idxNum==FTS3_FULLSCAN_SEARCH) );
+  assert( p->pSegments==0 );
+
+  /* In case the cursor has been used before, clear it now. */
+  sqlite3_finalize(pCsr->pStmt);
+  sqlite3_free(pCsr->aDoclist);
+  sqlite3Fts3ExprFree(pCsr->pExpr);
+  memset(&pCursor[1], 0, sizeof(Fts3Cursor)-sizeof(sqlite3_vtab_cursor));
+
+  if( idxNum!=FTS3_DOCID_SEARCH && idxNum!=FTS3_FULLSCAN_SEARCH ){
+    int iCol = idxNum-FTS3_FULLTEXT_SEARCH;
+    const char *zQuery = (const char *)sqlite3_value_text(apVal[0]);
+
+    if( zQuery==0 && sqlite3_value_type(apVal[0])!=SQLITE_NULL ){
+      return SQLITE_NOMEM;
+    }
+
+    rc = sqlite3Fts3ExprParse(p->pTokenizer, p->azColumn, p->nColumn, 
+        iCol, zQuery, -1, &pCsr->pExpr
+    );
+    if( rc!=SQLITE_OK ){
+      if( rc==SQLITE_ERROR ){
+        p->base.zErrMsg = sqlite3_mprintf("malformed MATCH expression: [%s]",
+                                          zQuery);
+      }
+      return rc;
+    }
+
+    rc = sqlite3Fts3ReadLock(p);
+    if( rc!=SQLITE_OK ) return rc;
+
+    rc = fts3EvalExpr(pCsr, pCsr->pExpr, &pCsr->aDoclist, &pCsr->nDoclist, 0);
+    sqlite3Fts3SegmentsClose(p);
+    if( rc!=SQLITE_OK ) return rc;
+    pCsr->pNextId = pCsr->aDoclist;
+    pCsr->iPrevId = 0;
+  }
+
+  /* Compile a SELECT statement for this cursor. For a full-table-scan, the
+  ** statement loops through all rows of the %_content table. For a
+  ** full-text query or docid lookup, the statement retrieves a single
+  ** row by docid.
+  */
+  zSql = (char *)azSql[idxNum==FTS3_FULLSCAN_SEARCH];
+  zSql = sqlite3_mprintf(zSql, p->zReadExprlist, p->zDb, p->zName);
+  if( !zSql ){
+    rc = SQLITE_NOMEM;
+  }else{
+    rc = sqlite3_prepare_v2(p->db, zSql, -1, &pCsr->pStmt, 0);
+    sqlite3_free(zSql);
+  }
+  if( rc==SQLITE_OK && idxNum==FTS3_DOCID_SEARCH ){
+    rc = sqlite3_bind_value(pCsr->pStmt, 1, apVal[0]);
+  }
+  pCsr->eSearch = (i16)idxNum;
+
+  if( rc!=SQLITE_OK ) return rc;
+  return fts3NextMethod(pCursor);
+}
+
+/* 
+** This is the xEof method of the virtual table. SQLite calls this 
+** routine to find out if it has reached the end of a result set.
+*/
+static int fts3EofMethod(sqlite3_vtab_cursor *pCursor){
+  return ((Fts3Cursor *)pCursor)->isEof;
+}
+
+/* 
+** This is the xRowid method. The SQLite core calls this routine to
+** retrieve the rowid for the current row of the result set. fts3
+** exposes %_content.docid as the rowid for the virtual table. The
+** rowid should be written to *pRowid.
+*/
+static int fts3RowidMethod(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
+  Fts3Cursor *pCsr = (Fts3Cursor *) pCursor;
+  if( pCsr->aDoclist ){
+    *pRowid = pCsr->iPrevId;
+  }else{
+    /* This branch runs if the query is implemented using a full-table scan
+    ** (not using the full-text index). In this case grab the rowid from the
+    ** SELECT statement.
+    */
+    assert( pCsr->isRequireSeek==0 );
+    *pRowid = sqlite3_column_int64(pCsr->pStmt, 0);
+  }
+  return SQLITE_OK;
+}
+
+/* 
+** This is the xColumn method, called by SQLite to request a value from
+** the row that the supplied cursor currently points to.
+*/
+static int fts3ColumnMethod(
+  sqlite3_vtab_cursor *pCursor,   /* Cursor to retrieve value from */
+  sqlite3_context *pContext,      /* Context for sqlite3_result_xxx() calls */
+  int iCol                        /* Index of column to read value from */
+){
+  int rc;                         /* Return Code */
+  Fts3Cursor *pCsr = (Fts3Cursor *) pCursor;
+  Fts3Table *p = (Fts3Table *)pCursor->pVtab;
+
+  /* The column value supplied by SQLite must be in range. */
+  assert( iCol>=0 && iCol<=p->nColumn+1 );
+
+  if( iCol==p->nColumn+1 ){
+    /* This call is a request for the "docid" column. Since "docid" is an 
+    ** alias for "rowid", use the xRowid() method to obtain the value.
+    */
+    sqlite3_int64 iRowid;
+    rc = fts3RowidMethod(pCursor, &iRowid);
+    sqlite3_result_int64(pContext, iRowid);
+  }else if( iCol==p->nColumn ){
+    /* The extra column whose name is the same as the table.
+    ** Return a blob which is a pointer to the cursor.
+    */
+    sqlite3_result_blob(pContext, &pCsr, sizeof(pCsr), SQLITE_TRANSIENT);
+    rc = SQLITE_OK;
+  }else{
+    rc = fts3CursorSeek(0, pCsr);
+    if( rc==SQLITE_OK ){
+      sqlite3_result_value(pContext, sqlite3_column_value(pCsr->pStmt, iCol+1));
+    }
+  }
+  return rc;
+}
+
+/* 
+** This function is the implementation of the xUpdate callback used by 
+** FTS3 virtual tables. It is invoked by SQLite each time a row is to be
+** inserted, updated or deleted.
+*/
+static int fts3UpdateMethod(
+  sqlite3_vtab *pVtab,            /* Virtual table handle */
+  int nArg,                       /* Size of argument array */
+  sqlite3_value **apVal,          /* Array of arguments */
+  sqlite_int64 *pRowid            /* OUT: The affected (or effected) rowid */
+){
+  return sqlite3Fts3UpdateMethod(pVtab, nArg, apVal, pRowid);
+}
+
+/*
+** Implementation of xSync() method. Flush the contents of the pending-terms
+** hash-table to the database.
+*/
+static int fts3SyncMethod(sqlite3_vtab *pVtab){
+  int rc = sqlite3Fts3PendingTermsFlush((Fts3Table *)pVtab);
+  sqlite3Fts3SegmentsClose((Fts3Table *)pVtab);
+  return rc;
+}
+
+/*
+** Implementation of xBegin() method. This is a no-op.
+*/
+static int fts3BeginMethod(sqlite3_vtab *pVtab){
+  UNUSED_PARAMETER(pVtab);
+  assert( ((Fts3Table *)pVtab)->nPendingData==0 );
+  return SQLITE_OK;
+}
+
+/*
+** Implementation of xCommit() method. This is a no-op. The contents of
+** the pending-terms hash-table have already been flushed into the database
+** by fts3SyncMethod().
+*/
+static int fts3CommitMethod(sqlite3_vtab *pVtab){
+  UNUSED_PARAMETER(pVtab);
+  assert( ((Fts3Table *)pVtab)->nPendingData==0 );
+  return SQLITE_OK;
+}
+
+/*
+** Implementation of xRollback(). Discard the contents of the pending-terms
+** hash-table. Any changes made to the database are reverted by SQLite.
+*/
+static int fts3RollbackMethod(sqlite3_vtab *pVtab){
+  sqlite3Fts3PendingTermsClear((Fts3Table *)pVtab);
+  return SQLITE_OK;
+}
+
+/*
+** Load the doclist associated with expression pExpr to pExpr->aDoclist.
+** The loaded doclist contains positions as well as the document ids.
+** This is used by the matchinfo(), snippet() and offsets() auxillary
+** functions.
+*/
+int sqlite3Fts3ExprLoadDoclist(Fts3Cursor *pCsr, Fts3Expr *pExpr){
   int rc;
-
-  FTSTRACE(("FTS3 Filter %p\n",pCursor));
-
-  /* If the cursor has a statement that was not prepared according to
-  ** idxNum, clear it.  I believe all calls to fulltextFilter with a
-  ** given cursor will have the same idxNum , but in this case it's
-  ** easy to be safe.
+  assert( pExpr->eType==FTSQUERY_PHRASE && pExpr->pPhrase );
+  assert( pCsr->eEvalmode==FTS3_EVAL_NEXT );
+  rc = fts3EvalExpr(pCsr, pExpr, &pExpr->aDoclist, &pExpr->nDoclist, 1);
+  return rc;
+}
+
+int sqlite3Fts3ExprLoadFtDoclist(
+  Fts3Cursor *pCsr, 
+  Fts3Expr *pExpr,
+  char **paDoclist,
+  int *pnDoclist
+){
+  int rc;
+  assert( pCsr->eEvalmode==FTS3_EVAL_NEXT );
+  assert( pExpr->eType==FTSQUERY_PHRASE && pExpr->pPhrase );
+  pCsr->eEvalmode = FTS3_EVAL_MATCHINFO;
+  rc = fts3EvalExpr(pCsr, pExpr, paDoclist, pnDoclist, 1);
+  pCsr->eEvalmode = FTS3_EVAL_NEXT;
+  return rc;
+}
+
+/*
+** After ExprLoadDoclist() (see above) has been called, this function is
+** used to iterate/search through the position lists that make up the doclist
+** stored in pExpr->aDoclist.
+*/
+char *sqlite3Fts3FindPositions(
+  Fts3Expr *pExpr,                /* Access this expressions doclist */
+  sqlite3_int64 iDocid,           /* Docid associated with requested pos-list */
+  int iCol                        /* Column of requested pos-list */
+){
+  assert( pExpr->isLoaded );
+  if( pExpr->aDoclist ){
+    char *pEnd = &pExpr->aDoclist[pExpr->nDoclist];
+    char *pCsr;
+
+    if( pExpr->pCurrent==0 ){
+      pExpr->pCurrent = pExpr->aDoclist;
+      pExpr->iCurrent = 0;
+      pExpr->pCurrent += sqlite3Fts3GetVarint(pExpr->pCurrent,&pExpr->iCurrent);
+    }
+    pCsr = pExpr->pCurrent;
+    assert( pCsr );
+
+    while( pCsr<pEnd ){
+      if( pExpr->iCurrent<iDocid ){
+        fts3PoslistCopy(0, &pCsr);
+        if( pCsr<pEnd ){
+          fts3GetDeltaVarint(&pCsr, &pExpr->iCurrent);
+        }
+        pExpr->pCurrent = pCsr;
+      }else{
+        if( pExpr->iCurrent==iDocid ){
+          int iThis = 0;
+          if( iCol<0 ){
+            /* If iCol is negative, return a pointer to the start of the
+            ** position-list (instead of a pointer to the start of a list
+            ** of offsets associated with a specific column).
+            */
+            return pCsr;
+          }
+          while( iThis<iCol ){
+            fts3ColumnlistCopy(0, &pCsr);
+            if( *pCsr==0x00 ) return 0;
+            pCsr++;
+            pCsr += sqlite3Fts3GetVarint32(pCsr, &iThis);
+          }
+          if( iCol==iThis && (*pCsr&0xFE) ) return pCsr;
+        }
+        return 0;
+      }
+    }
+  }
+
+  return 0;
+}
+
+/*
+** Helper function used by the implementation of the overloaded snippet(),
+** offsets() and optimize() SQL functions.
+**
+** If the value passed as the third argument is a blob of size
+** sizeof(Fts3Cursor*), then the blob contents are copied to the 
+** output variable *ppCsr and SQLITE_OK is returned. Otherwise, an error
+** message is written to context pContext and SQLITE_ERROR returned. The
+** string passed via zFunc is used as part of the error message.
+*/
+static int fts3FunctionArg(
+  sqlite3_context *pContext,      /* SQL function call context */
+  const char *zFunc,              /* Function name */
+  sqlite3_value *pVal,            /* argv[0] passed to function */
+  Fts3Cursor **ppCsr              /* OUT: Store cursor handle here */
+){
+  Fts3Cursor *pRet;
+  if( sqlite3_value_type(pVal)!=SQLITE_BLOB 
+   || sqlite3_value_bytes(pVal)!=sizeof(Fts3Cursor *)
+  ){
+    char *zErr = sqlite3_mprintf("illegal first argument to %s", zFunc);
+    sqlite3_result_error(pContext, zErr, -1);
+    sqlite3_free(zErr);
+    return SQLITE_ERROR;
+  }
+  memcpy(&pRet, sqlite3_value_blob(pVal), sizeof(Fts3Cursor *));
+  *ppCsr = pRet;
+  return SQLITE_OK;
+}
+
+/*
+** Implementation of the snippet() function for FTS3
+*/
+static void fts3SnippetFunc(
+  sqlite3_context *pContext,      /* SQLite function call context */
+  int nVal,                       /* Size of apVal[] array */
+  sqlite3_value **apVal           /* Array of arguments */
+){
+  Fts3Cursor *pCsr;               /* Cursor handle passed through apVal[0] */
+  const char *zStart = "<b>";
+  const char *zEnd = "</b>";
+  const char *zEllipsis = "<b>...</b>";
+  int iCol = -1;
+  int nToken = 15;                /* Default number of tokens in snippet */
+
+  /* There must be at least one argument passed to this function (otherwise
+  ** the non-overloaded version would have been called instead of this one).
   */
-  if( c->pStmt && c->iCursorType!=idxNum ){
-    sqlite3_finalize(c->pStmt);
-    c->pStmt = NULL;
-  }
-
-  /* Get a fresh statement appropriate to idxNum. */
-  /* TODO(shess): Add a prepared-statement cache in the vt structure.
-  ** The cache must handle multiple open cursors.  Easier to cache the
-  ** statement variants at the vt to reduce malloc/realloc/free here.
-  ** Or we could have a StringBuffer variant which allowed stack
-  ** construction for small values.
-  */
-  if( !c->pStmt ){
-    StringBuffer sb;
-    initStringBuffer(&sb);
-    append(&sb, "SELECT docid, ");
-    appendList(&sb, v->nColumn, v->azContentColumn);
-    append(&sb, " FROM %_content");
-    if( idxNum!=QUERY_GENERIC ) append(&sb, " WHERE docid = ?");
-    rc = sql_prepare(v->db, v->zDb, v->zName, &c->pStmt,
-                     stringBufferData(&sb));
-    stringBufferDestroy(&sb);
-    if( rc!=SQLITE_OK ) return rc;
-    c->iCursorType = idxNum;
-  }else{
-    sqlite3_reset(c->pStmt);
-    assert( c->iCursorType==idxNum );
-  }
-
-  switch( idxNum ){
-    case QUERY_GENERIC:
+  assert( nVal>=1 );
+
+  if( nVal>6 ){
+    sqlite3_result_error(pContext, 
+        "wrong number of arguments to function snippet()", -1);
+    return;
+  }
+  if( fts3FunctionArg(pContext, "snippet", apVal[0], &pCsr) ) return;
+
+  switch( nVal ){
+    case 6: nToken = sqlite3_value_int(apVal[5]);
+    case 5: iCol = sqlite3_value_int(apVal[4]);
+    case 4: zEllipsis = (const char*)sqlite3_value_text(apVal[3]);
+    case 3: zEnd = (const char*)sqlite3_value_text(apVal[2]);
+    case 2: zStart = (const char*)sqlite3_value_text(apVal[1]);
+  }
+  if( !zEllipsis || !zEnd || !zStart ){
+    sqlite3_result_error_nomem(pContext);
+  }else if( SQLITE_OK==fts3CursorSeek(pContext, pCsr) ){
+    sqlite3Fts3Snippet(pContext, pCsr, zStart, zEnd, zEllipsis, iCol, nToken);
+  }
+}
+
+/*
+** Implementation of the offsets() function for FTS3
+*/
+static void fts3OffsetsFunc(
+  sqlite3_context *pContext,      /* SQLite function call context */
+  int nVal,                       /* Size of argument array */
+  sqlite3_value **apVal           /* Array of arguments */
+){
+  Fts3Cursor *pCsr;               /* Cursor handle passed through apVal[0] */
+
+  UNUSED_PARAMETER(nVal);
+
+  assert( nVal==1 );
+  if( fts3FunctionArg(pContext, "offsets", apVal[0], &pCsr) ) return;
+  assert( pCsr );
+  if( SQLITE_OK==fts3CursorSeek(pContext, pCsr) ){
+    sqlite3Fts3Offsets(pContext, pCsr);
+  }
+}
+
+/* 
+** Implementation of the special optimize() function for FTS3. This 
+** function merges all segments in the database to a single segment.
+** Example usage is:
+**
+**   SELECT optimize(t) FROM t LIMIT 1;
+**
+** where 't' is the name of an FTS3 table.
+*/
+static void fts3OptimizeFunc(
+  sqlite3_context *pContext,      /* SQLite function call context */
+  int nVal,                       /* Size of argument array */
+  sqlite3_value **apVal           /* Array of arguments */
+){
+  int rc;                         /* Return code */
+  Fts3Table *p;                   /* Virtual table handle */
+  Fts3Cursor *pCursor;            /* Cursor handle passed through apVal[0] */
+
+  UNUSED_PARAMETER(nVal);
+
+  assert( nVal==1 );
+  if( fts3FunctionArg(pContext, "optimize", apVal[0], &pCursor) ) return;
+  p = (Fts3Table *)pCursor->base.pVtab;
+  assert( p );
+
+  rc = sqlite3Fts3Optimize(p);
+
+  switch( rc ){
+    case SQLITE_OK:
+      sqlite3_result_text(pContext, "Index optimized", -1, SQLITE_STATIC);
       break;
-
-    case QUERY_DOCID:
-      rc = sqlite3_bind_int64(c->pStmt, 1, sqlite3_value_int64(argv[0]));
-      if( rc!=SQLITE_OK ) return rc;
+    case SQLITE_DONE:
+      sqlite3_result_text(pContext, "Index already optimal", -1, SQLITE_STATIC);
       break;
-
-    default:   /* full-text search */
-    {
-      int iCol = idxNum-QUERY_FULLTEXT;
-      const char *zQuery = (const char *)sqlite3_value_text(argv[0]);
-      assert( idxNum<=QUERY_FULLTEXT+v->nColumn);
-      assert( argc==1 );
-      if( c->result.nData!=0 ){
-        /* This case happens if the same cursor is used repeatedly. */
-        dlrDestroy(&c->reader);
-        dataBufferReset(&c->result);
-      }else{
-        dataBufferInit(&c->result, 0);
-      }
-      rc = fulltextQuery(v, iCol, zQuery, -1, &c->result, &c->pExpr);
-      if( rc!=SQLITE_OK ) return rc;
-      if( c->result.nData!=0 ){
-        dlrInit(&c->reader, DL_DOCIDS, c->result.pData, c->result.nData);
-      }
+    default:
+      sqlite3_result_error_code(pContext, rc);
       break;
-    }
-  }
-
-  return fulltextNext(pCursor);
-}
-
-/* This is the xEof method of the virtual table.  The SQLite core
-** calls this routine to find out if it has reached the end of
-** a query's results set.
-*/
-static int fulltextEof(sqlite3_vtab_cursor *pCursor){
-  fulltext_cursor *c = (fulltext_cursor *) pCursor;
-  return c->eof;
-}
-
-/* This is the xColumn method of the virtual table.  The SQLite
-** core calls this method during a query when it needs the value
-** of a column from the virtual table.  This method needs to use
-** one of the sqlite3_result_*() routines to store the requested
-** value back in the pContext.
-*/
-static int fulltextColumn(sqlite3_vtab_cursor *pCursor,
-                          sqlite3_context *pContext, int idxCol){
-  fulltext_cursor *c = (fulltext_cursor *) pCursor;
-  fulltext_vtab *v = cursor_vtab(c);
-
-  if( idxCol<v->nColumn ){
-    sqlite3_value *pVal = sqlite3_column_value(c->pStmt, idxCol+1);
-    sqlite3_result_value(pContext, pVal);
-  }else if( idxCol==v->nColumn ){
-    /* The extra column whose name is the same as the table.
-    ** Return a blob which is a pointer to the cursor
-    */
-    sqlite3_result_blob(pContext, &c, sizeof(c), SQLITE_TRANSIENT);
-  }else if( idxCol==v->nColumn+1 ){
-    /* The docid column, which is an alias for rowid. */
-    sqlite3_value *pVal = sqlite3_column_value(c->pStmt, 0);
-    sqlite3_result_value(pContext, pVal);
-  }
-  return SQLITE_OK;
-}
-
-/* This is the xRowid method.  The SQLite core calls this routine to
-** retrieve the rowid for the current row of the result set.  fts3
-** exposes %_content.docid as the rowid for the virtual table.  The
-** rowid should be written to *pRowid.
-*/
-static int fulltextRowid(sqlite3_vtab_cursor *pCursor, sqlite_int64 *pRowid){
-  fulltext_cursor *c = (fulltext_cursor *) pCursor;
-
-  *pRowid = sqlite3_column_int64(c->pStmt, 0);
-  return SQLITE_OK;
-}
-
-/* Add all terms in [zText] to pendingTerms table.  If [iColumn] > 0,
-** we also store positions and offsets in the hash table using that
-** column number.
-*/
-static int buildTerms(fulltext_vtab *v, sqlite_int64 iDocid,
-                      const char *zText, int iColumn){
-  sqlite3_tokenizer *pTokenizer = v->pTokenizer;
-  sqlite3_tokenizer_cursor *pCursor;
-  const char *pToken;
-  int nTokenBytes;
-  int iStartOffset, iEndOffset, iPosition;
-  int rc;
-
-  rc = pTokenizer->pModule->xOpen(pTokenizer, zText, -1, &pCursor);
-  if( rc!=SQLITE_OK ) return rc;
-
-  pCursor->pTokenizer = pTokenizer;
-  while( SQLITE_OK==(rc=pTokenizer->pModule->xNext(pCursor,
-                                                   &pToken, &nTokenBytes,
-                                                   &iStartOffset, &iEndOffset,
-                                                   &iPosition)) ){
-    DLCollector *p;
-    int nData;                   /* Size of doclist before our update. */
-
-    /* Positions can't be negative; we use -1 as a terminator
-     * internally.  Token can't be NULL or empty. */
-    if( iPosition<0 || pToken == NULL || nTokenBytes == 0 ){
-      rc = SQLITE_ERROR;
-      break;
-    }
-
-    p = fts3HashFind(&v->pendingTerms, pToken, nTokenBytes);
-    if( p==NULL ){
-      nData = 0;
-      p = dlcNew(iDocid, DL_DEFAULT);
-      fts3HashInsert(&v->pendingTerms, pToken, nTokenBytes, p);
-
-      /* Overhead for our hash table entry, the key, and the value. */
-      v->nPendingData += sizeof(struct fts3HashElem)+sizeof(*p)+nTokenBytes;
-    }else{
-      nData = p->b.nData;
-      if( p->dlw.iPrevDocid!=iDocid ) dlcNext(p, iDocid);
-    }
-    if( iColumn>=0 ){
-      dlcAddPos(p, iColumn, iPosition, iStartOffset, iEndOffset);
-    }
-
-    /* Accumulate data added by dlcNew or dlcNext, and dlcAddPos. */
-    v->nPendingData += p->b.nData-nData;
-  }
-
-  /* TODO(shess) Check return?  Should this be able to cause errors at
-  ** this point?  Actually, same question about sqlite3_finalize(),
-  ** though one could argue that failure there means that the data is
-  ** not durable.  *ponder*
-  */
-  pTokenizer->pModule->xClose(pCursor);
-  if( SQLITE_DONE == rc ) return SQLITE_OK;
-  return rc;
-}
-
-/* Add doclists for all terms in [pValues] to pendingTerms table. */
-static int insertTerms(fulltext_vtab *v, sqlite_int64 iDocid,
-                       sqlite3_value **pValues){
-  int i;
-  for(i = 0; i < v->nColumn ; ++i){
-    char *zText = (char*)sqlite3_value_text(pValues[i]);
-    int rc = buildTerms(v, iDocid, zText, i);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-  return SQLITE_OK;
-}
-
-/* Add empty doclists for all terms in the given row's content to
-** pendingTerms.
-*/
-static int deleteTerms(fulltext_vtab *v, sqlite_int64 iDocid){
-  const char **pValues;
-  int i, rc;
-
-  /* TODO(shess) Should we allow such tables at all? */
-  if( DL_DEFAULT==DL_DOCIDS ) return SQLITE_ERROR;
-
-  rc = content_select(v, iDocid, &pValues);
-  if( rc!=SQLITE_OK ) return rc;
-
-  for(i = 0 ; i < v->nColumn; ++i) {
-    rc = buildTerms(v, iDocid, pValues[i], -1);
-    if( rc!=SQLITE_OK ) break;
-  }
-
-  freeStringArray(v->nColumn, pValues);
-  return SQLITE_OK;
-}
-
-/* TODO(shess) Refactor the code to remove this forward decl. */
-static int initPendingTerms(fulltext_vtab *v, sqlite_int64 iDocid);
-
-/* Insert a row into the %_content table; set *piDocid to be the ID of the
-** new row.  Add doclists for terms to pendingTerms.
-*/
-static int index_insert(fulltext_vtab *v, sqlite3_value *pRequestDocid,
-                        sqlite3_value **pValues, sqlite_int64 *piDocid){
-  int rc;
-
-  rc = content_insert(v, pRequestDocid, pValues);  /* execute an SQL INSERT */
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* docid column is an alias for rowid. */
-  *piDocid = sqlite3_last_insert_rowid(v->db);
-  rc = initPendingTerms(v, *piDocid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return insertTerms(v, *piDocid, pValues);
-}
-
-/* Delete a row from the %_content table; add empty doclists for terms
-** to pendingTerms.
-*/
-static int index_delete(fulltext_vtab *v, sqlite_int64 iRow){
-  int rc = initPendingTerms(v, iRow);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = deleteTerms(v, iRow);
-  if( rc!=SQLITE_OK ) return rc;
-
-  return content_delete(v, iRow);  /* execute an SQL DELETE */
-}
-
-/* Update a row in the %_content table; add delete doclists to
-** pendingTerms for old terms not in the new data, add insert doclists
-** to pendingTerms for terms in the new data.
-*/
-static int index_update(fulltext_vtab *v, sqlite_int64 iRow,
-                        sqlite3_value **pValues){
-  int rc = initPendingTerms(v, iRow);
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* Generate an empty doclist for each term that previously appeared in this
-   * row. */
-  rc = deleteTerms(v, iRow);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = content_update(v, pValues, iRow);  /* execute an SQL UPDATE */
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* Now add positions for terms which appear in the updated row. */
-  return insertTerms(v, iRow, pValues);
-}
-
-/*******************************************************************/
-/* InteriorWriter is used to collect terms and block references into
-** interior nodes in %_segments.  See commentary at top of file for
-** format.
-*/
-
-/* How large interior nodes can grow. */
-#define INTERIOR_MAX 2048
-
-/* Minimum number of terms per interior node (except the root). This
-** prevents large terms from making the tree too skinny - must be >0
-** so that the tree always makes progress.  Note that the min tree
-** fanout will be INTERIOR_MIN_TERMS+1.
-*/
-#define INTERIOR_MIN_TERMS 7
-#if INTERIOR_MIN_TERMS<1
-# error INTERIOR_MIN_TERMS must be greater than 0.
-#endif
-
-/* ROOT_MAX controls how much data is stored inline in the segment
-** directory.
-*/
-/* TODO(shess) Push ROOT_MAX down to whoever is writing things.  It's
-** only here so that interiorWriterRootInfo() and leafWriterRootInfo()
-** can both see it, but if the caller passed it in, we wouldn't even
-** need a define.
-*/
-#define ROOT_MAX 1024
-#if ROOT_MAX<VARINT_MAX*2
-# error ROOT_MAX must have enough space for a header.
-#endif
-
-/* InteriorBlock stores a linked-list of interior blocks while a lower
-** layer is being constructed.
-*/
-typedef struct InteriorBlock {
-  DataBuffer term;           /* Leftmost term in block's subtree. */
-  DataBuffer data;           /* Accumulated data for the block. */
-  struct InteriorBlock *next;
-} InteriorBlock;
-
-static InteriorBlock *interiorBlockNew(int iHeight, sqlite_int64 iChildBlock,
-                                       const char *pTerm, int nTerm){
-  InteriorBlock *block = sqlite3_malloc(sizeof(InteriorBlock));
-  char c[VARINT_MAX+VARINT_MAX];
-  int n;
-
-  if( block ){
-    memset(block, 0, sizeof(*block));
-    dataBufferInit(&block->term, 0);
-    dataBufferReplace(&block->term, pTerm, nTerm);
-
-    n = fts3PutVarint(c, iHeight);
-    n += fts3PutVarint(c+n, iChildBlock);
-    dataBufferInit(&block->data, INTERIOR_MAX);
-    dataBufferReplace(&block->data, c, n);
-  }
-  return block;
-}
-
-#ifndef NDEBUG
-/* Verify that the data is readable as an interior node. */
-static void interiorBlockValidate(InteriorBlock *pBlock){
-  const char *pData = pBlock->data.pData;
-  int nData = pBlock->data.nData;
-  int n, iDummy;
-  sqlite_int64 iBlockid;
-
-  assert( nData>0 );
-  assert( pData!=0 );
-  assert( pData+nData>pData );
-
-  /* Must lead with height of node as a varint(n), n>0 */
-  n = fts3GetVarint32(pData, &iDummy);
-  assert( n>0 );
-  assert( iDummy>0 );
-  assert( n<nData );
-  pData += n;
-  nData -= n;
-
-  /* Must contain iBlockid. */
-  n = fts3GetVarint(pData, &iBlockid);
-  assert( n>0 );
-  assert( n<=nData );
-  pData += n;
-  nData -= n;
-
-  /* Zero or more terms of positive length */
-  if( nData!=0 ){
-    /* First term is not delta-encoded. */
-    n = fts3GetVarint32(pData, &iDummy);
-    assert( n>0 );
-    assert( iDummy>0 );
-    assert( n+iDummy>0);
-    assert( n+iDummy<=nData );
-    pData += n+iDummy;
-    nData -= n+iDummy;
-
-    /* Following terms delta-encoded. */
-    while( nData!=0 ){
-      /* Length of shared prefix. */
-      n = fts3GetVarint32(pData, &iDummy);
-      assert( n>0 );
-      assert( iDummy>=0 );
-      assert( n<nData );
-      pData += n;
-      nData -= n;
-
-      /* Length and data of distinct suffix. */
-      n = fts3GetVarint32(pData, &iDummy);
-      assert( n>0 );
-      assert( iDummy>0 );
-      assert( n+iDummy>0);
-      assert( n+iDummy<=nData );
-      pData += n+iDummy;
-      nData -= n+iDummy;
-    }
-  }
-}
-#define ASSERT_VALID_INTERIOR_BLOCK(x) interiorBlockValidate(x)
-#else
-#define ASSERT_VALID_INTERIOR_BLOCK(x) assert( 1 )
-#endif
-
-typedef struct InteriorWriter {
-  int iHeight;                   /* from 0 at leaves. */
-  InteriorBlock *first, *last;
-  struct InteriorWriter *parentWriter;
-
-  DataBuffer term;               /* Last term written to block "last". */
-  sqlite_int64 iOpeningChildBlock; /* First child block in block "last". */
-#ifndef NDEBUG
-  sqlite_int64 iLastChildBlock;  /* for consistency checks. */
-#endif
-} InteriorWriter;
-
-/* Initialize an interior node where pTerm[nTerm] marks the leftmost
-** term in the tree.  iChildBlock is the leftmost child block at the
-** next level down the tree.
-*/
-static void interiorWriterInit(int iHeight, const char *pTerm, int nTerm,
-                               sqlite_int64 iChildBlock,
-                               InteriorWriter *pWriter){
-  InteriorBlock *block;
-  assert( iHeight>0 );
-  CLEAR(pWriter);
-
-  pWriter->iHeight = iHeight;
-  pWriter->iOpeningChildBlock = iChildBlock;
-#ifndef NDEBUG
-  pWriter->iLastChildBlock = iChildBlock;
-#endif
-  block = interiorBlockNew(iHeight, iChildBlock, pTerm, nTerm);
-  pWriter->last = pWriter->first = block;
-  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);
-  dataBufferInit(&pWriter->term, 0);
-}
-
-/* Append the child node rooted at iChildBlock to the interior node,
-** with pTerm[nTerm] as the leftmost term in iChildBlock's subtree.
-*/
-static void interiorWriterAppend(InteriorWriter *pWriter,
-                                 const char *pTerm, int nTerm,
-                                 sqlite_int64 iChildBlock){
-  char c[VARINT_MAX+VARINT_MAX];
-  int n, nPrefix = 0;
-
-  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);
-
-  /* The first term written into an interior node is actually
-  ** associated with the second child added (the first child was added
-  ** in interiorWriterInit, or in the if clause at the bottom of this
-  ** function).  That term gets encoded straight up, with nPrefix left
-  ** at 0.
-  */
-  if( pWriter->term.nData==0 ){
-    n = fts3PutVarint(c, nTerm);
-  }else{
-    while( nPrefix<pWriter->term.nData &&
-           pTerm[nPrefix]==pWriter->term.pData[nPrefix] ){
-      nPrefix++;
-    }
-
-    n = fts3PutVarint(c, nPrefix);
-    n += fts3PutVarint(c+n, nTerm-nPrefix);
-  }
-
-#ifndef NDEBUG
-  pWriter->iLastChildBlock++;
-#endif
-  assert( pWriter->iLastChildBlock==iChildBlock );
-
-  /* Overflow to a new block if the new term makes the current block
-  ** too big, and the current block already has enough terms.
-  */
-  if( pWriter->last->data.nData+n+nTerm-nPrefix>INTERIOR_MAX &&
-      iChildBlock-pWriter->iOpeningChildBlock>INTERIOR_MIN_TERMS ){
-    pWriter->last->next = interiorBlockNew(pWriter->iHeight, iChildBlock,
-                                           pTerm, nTerm);
-    pWriter->last = pWriter->last->next;
-    pWriter->iOpeningChildBlock = iChildBlock;
-    dataBufferReset(&pWriter->term);
-  }else{
-    dataBufferAppend2(&pWriter->last->data, c, n,
-                      pTerm+nPrefix, nTerm-nPrefix);
-    dataBufferReplace(&pWriter->term, pTerm, nTerm);
-  }
-  ASSERT_VALID_INTERIOR_BLOCK(pWriter->last);
-}
-
-/* Free the space used by pWriter, including the linked-list of
-** InteriorBlocks, and parentWriter, if present.
-*/
-static int interiorWriterDestroy(InteriorWriter *pWriter){
-  InteriorBlock *block = pWriter->first;
-
-  while( block!=NULL ){
-    InteriorBlock *b = block;
-    block = block->next;
-    dataBufferDestroy(&b->term);
-    dataBufferDestroy(&b->data);
-    sqlite3_free(b);
-  }
-  if( pWriter->parentWriter!=NULL ){
-    interiorWriterDestroy(pWriter->parentWriter);
-    sqlite3_free(pWriter->parentWriter);
-  }
-  dataBufferDestroy(&pWriter->term);
-  SCRAMBLE(pWriter);
-  return SQLITE_OK;
-}
-
-/* If pWriter can fit entirely in ROOT_MAX, return it as the root info
-** directly, leaving *piEndBlockid unchanged.  Otherwise, flush
-** pWriter to %_segments, building a new layer of interior nodes, and
-** recursively ask for their root into.
-*/
-static int interiorWriterRootInfo(fulltext_vtab *v, InteriorWriter *pWriter,
-                                  char **ppRootInfo, int *pnRootInfo,
-                                  sqlite_int64 *piEndBlockid){
-  InteriorBlock *block = pWriter->first;
-  sqlite_int64 iBlockid = 0;
-  int rc;
-
-  /* If we can fit the segment inline */
-  if( block==pWriter->last && block->data.nData<ROOT_MAX ){
-    *ppRootInfo = block->data.pData;
-    *pnRootInfo = block->data.nData;
-    return SQLITE_OK;
-  }
-
-  /* Flush the first block to %_segments, and create a new level of
-  ** interior node.
-  */
-  ASSERT_VALID_INTERIOR_BLOCK(block);
-  rc = block_insert(v, block->data.pData, block->data.nData, &iBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-  *piEndBlockid = iBlockid;
-
-  pWriter->parentWriter = sqlite3_malloc(sizeof(*pWriter->parentWriter));
-  interiorWriterInit(pWriter->iHeight+1,
-                     block->term.pData, block->term.nData,
-                     iBlockid, pWriter->parentWriter);
-
-  /* Flush additional blocks and append to the higher interior
-  ** node.
-  */
-  for(block=block->next; block!=NULL; block=block->next){
-    ASSERT_VALID_INTERIOR_BLOCK(block);
-    rc = block_insert(v, block->data.pData, block->data.nData, &iBlockid);
-    if( rc!=SQLITE_OK ) return rc;
-    *piEndBlockid = iBlockid;
-
-    interiorWriterAppend(pWriter->parentWriter,
-                         block->term.pData, block->term.nData, iBlockid);
-  }
-
-  /* Parent node gets the chance to be the root. */
-  return interiorWriterRootInfo(v, pWriter->parentWriter,
-                                ppRootInfo, pnRootInfo, piEndBlockid);
-}
-
-/****************************************************************/
-/* InteriorReader is used to read off the data from an interior node
-** (see comment at top of file for the format).
-*/
-typedef struct InteriorReader {
-  const char *pData;
-  int nData;
-
-  DataBuffer term;          /* previous term, for decoding term delta. */
-
-  sqlite_int64 iBlockid;
-} InteriorReader;
-
-static void interiorReaderDestroy(InteriorReader *pReader){
-  dataBufferDestroy(&pReader->term);
-  SCRAMBLE(pReader);
-}
-
-static int interiorReaderInit(const char *pData, int nData,
-                              InteriorReader *pReader){
-  int n, nTerm;
-
-  /* These conditions are checked and met by the callers. */
-  assert( nData>0 );
-  assert( pData[0]!='\0' );
-
-  CLEAR(pReader);
-
-  /* Decode the base blockid, and set the cursor to the first term. */
-  n = fts3GetVarintSafe(pData+1, &pReader->iBlockid, nData-1);
-  if( !n ) return SQLITE_CORRUPT_BKPT;
-  pReader->pData = pData+1+n;
-  pReader->nData = nData-(1+n);
-
-  /* A single-child interior node (such as when a leaf node was too
-  ** large for the segment directory) won't have any terms.
-  ** Otherwise, decode the first term.
-  */
-  if( pReader->nData==0 ){
-    dataBufferInit(&pReader->term, 0);
-  }else{
-    n = fts3GetVarint32Safe(pReader->pData, &nTerm, pReader->nData);
-    if( !n || nTerm<0 || nTerm>pReader->nData-n) return SQLITE_CORRUPT_BKPT;
-    dataBufferInit(&pReader->term, nTerm);
-    dataBufferReplace(&pReader->term, pReader->pData+n, nTerm);
-    pReader->pData += n+nTerm;
-    pReader->nData -= n+nTerm;
-  }
-  return SQLITE_OK;
-}
-
-static int interiorReaderAtEnd(InteriorReader *pReader){
-  return pReader->term.nData<=0;
-}
-
-static sqlite_int64 interiorReaderCurrentBlockid(InteriorReader *pReader){
-  return pReader->iBlockid;
-}
-
-static int interiorReaderTermBytes(InteriorReader *pReader){
-  assert( !interiorReaderAtEnd(pReader) );
-  return pReader->term.nData;
-}
-static const char *interiorReaderTerm(InteriorReader *pReader){
-  assert( !interiorReaderAtEnd(pReader) );
-  return pReader->term.pData;
-}
-
-/* Step forward to the next term in the node. */
-static int interiorReaderStep(InteriorReader *pReader){
-  assert( !interiorReaderAtEnd(pReader) );
-
-  /* If the last term has been read, signal eof, else construct the
-  ** next term.
-  */
-  if( pReader->nData==0 ){
-    dataBufferReset(&pReader->term);
-  }else{
-    int n, nPrefix, nSuffix;
-
-    n = fts3GetVarint32Safe(pReader->pData, &nPrefix, pReader->nData);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    pReader->nData -= n;
-    pReader->pData += n;
-    n = fts3GetVarint32Safe(pReader->pData, &nSuffix, pReader->nData);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    pReader->nData -= n;
-    pReader->pData += n;
-    if( nSuffix<0 || nSuffix>pReader->nData ) return SQLITE_CORRUPT_BKPT;
-    if( nPrefix<0 || nPrefix>pReader->term.nData ) return SQLITE_CORRUPT_BKPT;
-
-    /* Truncate the current term and append suffix data. */
-    pReader->term.nData = nPrefix;
-    dataBufferAppend(&pReader->term, pReader->pData, nSuffix);
-
-    pReader->pData += nSuffix;
-    pReader->nData -= nSuffix;
-  }
-  pReader->iBlockid++;
-  return SQLITE_OK;
-}
-
-/* Compare the current term to pTerm[nTerm], returning strcmp-style
-** results.  If isPrefix, equality means equal through nTerm bytes.
-*/
-static int interiorReaderTermCmp(InteriorReader *pReader,
-                                 const char *pTerm, int nTerm, int isPrefix){
-  const char *pReaderTerm = interiorReaderTerm(pReader);
-  int nReaderTerm = interiorReaderTermBytes(pReader);
-  int c, n = nReaderTerm<nTerm ? nReaderTerm : nTerm;
-
-  if( n==0 ){
-    if( nReaderTerm>0 ) return -1;
-    if( nTerm>0 ) return 1;
-    return 0;
-  }
-
-  c = memcmp(pReaderTerm, pTerm, n);
-  if( c!=0 ) return c;
-  if( isPrefix && n==nTerm ) return 0;
-  return nReaderTerm - nTerm;
-}
-
-/****************************************************************/
-/* LeafWriter is used to collect terms and associated doclist data
-** into leaf blocks in %_segments (see top of file for format info).
-** Expected usage is:
-**
-** LeafWriter writer;
-** leafWriterInit(0, 0, &writer);
-** while( sorted_terms_left_to_process ){
-**   // data is doclist data for that term.
-**   rc = leafWriterStep(v, &writer, pTerm, nTerm, pData, nData);
-**   if( rc!=SQLITE_OK ) goto err;
-** }
-** rc = leafWriterFinalize(v, &writer);
-**err:
-** leafWriterDestroy(&writer);
-** return rc;
-**
-** leafWriterStep() may write a collected leaf out to %_segments.
-** leafWriterFinalize() finishes writing any buffered data and stores
-** a root node in %_segdir.  leafWriterDestroy() frees all buffers and
-** InteriorWriters allocated as part of writing this segment.
-**
-** TODO(shess) Document leafWriterStepMerge().
-*/
-
-/* Put terms with data this big in their own block. */
-#define STANDALONE_MIN 1024
-
-/* Keep leaf blocks below this size. */
-#define LEAF_MAX 2048
-
-typedef struct LeafWriter {
-  int iLevel;
-  int idx;
-  sqlite_int64 iStartBlockid;     /* needed to create the root info */
-  sqlite_int64 iEndBlockid;       /* when we're done writing. */
-
-  DataBuffer term;                /* previous encoded term */
-  DataBuffer data;                /* encoding buffer */
-
-  /* bytes of first term in the current node which distinguishes that
-  ** term from the last term of the previous node.
-  */
-  int nTermDistinct;
-
-  InteriorWriter parentWriter;    /* if we overflow */
-  int has_parent;
-} LeafWriter;
-
-static void leafWriterInit(int iLevel, int idx, LeafWriter *pWriter){
-  CLEAR(pWriter);
-  pWriter->iLevel = iLevel;
-  pWriter->idx = idx;
-
-  dataBufferInit(&pWriter->term, 32);
-
-  /* Start out with a reasonably sized block, though it can grow. */
-  dataBufferInit(&pWriter->data, LEAF_MAX);
-}
-
-#ifndef NDEBUG
-/* Verify that the data is readable as a leaf node. */
-static void leafNodeValidate(const char *pData, int nData){
-  int n, iDummy;
-
-  if( nData==0 ) return;
-  assert( nData>0 );
-  assert( pData!=0 );
-  assert( pData+nData>pData );
-
-  /* Must lead with a varint(0) */
-  n = fts3GetVarint32(pData, &iDummy);
-  assert( iDummy==0 );
-  assert( n>0 );
-  assert( n<nData );
-  pData += n;
-  nData -= n;
-
-  /* Leading term length and data must fit in buffer. */
-  n = fts3GetVarint32(pData, &iDummy);
-  assert( n>0 );
-  assert( iDummy>0 );
-  assert( n+iDummy>0 );
-  assert( n+iDummy<nData );
-  pData += n+iDummy;
-  nData -= n+iDummy;
-
-  /* Leading term's doclist length and data must fit. */
-  n = fts3GetVarint32(pData, &iDummy);
-  assert( n>0 );
-  assert( iDummy>0 );
-  assert( n+iDummy>0 );
-  assert( n+iDummy<=nData );
-  ASSERT_VALID_DOCLIST(DL_DEFAULT, pData+n, iDummy, NULL);
-  pData += n+iDummy;
-  nData -= n+iDummy;
-
-  /* Verify that trailing terms and doclists also are readable. */
-  while( nData!=0 ){
-    n = fts3GetVarint32(pData, &iDummy);
-    assert( n>0 );
-    assert( iDummy>=0 );
-    assert( n<nData );
-    pData += n;
-    nData -= n;
-    n = fts3GetVarint32(pData, &iDummy);
-    assert( n>0 );
-    assert( iDummy>0 );
-    assert( n+iDummy>0 );
-    assert( n+iDummy<nData );
-    pData += n+iDummy;
-    nData -= n+iDummy;
-
-    n = fts3GetVarint32(pData, &iDummy);
-    assert( n>0 );
-    assert( iDummy>0 );
-    assert( n+iDummy>0 );
-    assert( n+iDummy<=nData );
-    ASSERT_VALID_DOCLIST(DL_DEFAULT, pData+n, iDummy, NULL);
-    pData += n+iDummy;
-    nData -= n+iDummy;
-  }
-}
-#define ASSERT_VALID_LEAF_NODE(p, n) leafNodeValidate(p, n)
-#else
-#define ASSERT_VALID_LEAF_NODE(p, n) assert( 1 )
-#endif
-
-/* Flush the current leaf node to %_segments, and adding the resulting
-** blockid and the starting term to the interior node which will
-** contain it.
-*/
-static int leafWriterInternalFlush(fulltext_vtab *v, LeafWriter *pWriter,
-                                   int iData, int nData){
-  sqlite_int64 iBlockid = 0;
-  const char *pStartingTerm;
-  int nStartingTerm, rc, n;
-
-  /* Must have the leading varint(0) flag, plus at least some
-  ** valid-looking data.
-  */
-  assert( nData>2 );
-  assert( iData>=0 );
-  assert( iData+nData<=pWriter->data.nData );
-  ASSERT_VALID_LEAF_NODE(pWriter->data.pData+iData, nData);
-
-  rc = block_insert(v, pWriter->data.pData+iData, nData, &iBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-  assert( iBlockid!=0 );
-
-  /* Reconstruct the first term in the leaf for purposes of building
-  ** the interior node.
-  */
-  n = fts3GetVarint32(pWriter->data.pData+iData+1, &nStartingTerm);
-  pStartingTerm = pWriter->data.pData+iData+1+n;
-  assert( pWriter->data.nData>iData+1+n+nStartingTerm );
-  assert( pWriter->nTermDistinct>0 );
-  assert( pWriter->nTermDistinct<=nStartingTerm );
-  nStartingTerm = pWriter->nTermDistinct;
-
-  if( pWriter->has_parent ){
-    interiorWriterAppend(&pWriter->parentWriter,
-                         pStartingTerm, nStartingTerm, iBlockid);
-  }else{
-    interiorWriterInit(1, pStartingTerm, nStartingTerm, iBlockid,
-                       &pWriter->parentWriter);
-    pWriter->has_parent = 1;
-  }
-
-  /* Track the span of this segment's leaf nodes. */
-  if( pWriter->iEndBlockid==0 ){
-    pWriter->iEndBlockid = pWriter->iStartBlockid = iBlockid;
-  }else{
-    pWriter->iEndBlockid++;
-    assert( iBlockid==pWriter->iEndBlockid );
-  }
-
-  return SQLITE_OK;
-}
-static int leafWriterFlush(fulltext_vtab *v, LeafWriter *pWriter){
-  int rc = leafWriterInternalFlush(v, pWriter, 0, pWriter->data.nData);
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* Re-initialize the output buffer. */
-  dataBufferReset(&pWriter->data);
-
-  return SQLITE_OK;
-}
-
-/* Fetch the root info for the segment.  If the entire leaf fits
-** within ROOT_MAX, then it will be returned directly, otherwise it
-** will be flushed and the root info will be returned from the
-** interior node.  *piEndBlockid is set to the blockid of the last
-** interior or leaf node written to disk (0 if none are written at
-** all).
-*/
-static int leafWriterRootInfo(fulltext_vtab *v, LeafWriter *pWriter,
-                              char **ppRootInfo, int *pnRootInfo,
-                              sqlite_int64 *piEndBlockid){
-  /* we can fit the segment entirely inline */
-  if( !pWriter->has_parent && pWriter->data.nData<ROOT_MAX ){
-    *ppRootInfo = pWriter->data.pData;
-    *pnRootInfo = pWriter->data.nData;
-    *piEndBlockid = 0;
-    return SQLITE_OK;
-  }
-
-  /* Flush remaining leaf data. */
-  if( pWriter->data.nData>0 ){
-    int rc = leafWriterFlush(v, pWriter);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-
-  /* We must have flushed a leaf at some point. */
-  assert( pWriter->has_parent );
-
-  /* Tenatively set the end leaf blockid as the end blockid.  If the
-  ** interior node can be returned inline, this will be the final
-  ** blockid, otherwise it will be overwritten by
-  ** interiorWriterRootInfo().
-  */
-  *piEndBlockid = pWriter->iEndBlockid;
-
-  return interiorWriterRootInfo(v, &pWriter->parentWriter,
-                                ppRootInfo, pnRootInfo, piEndBlockid);
-}
-
-/* Collect the rootInfo data and store it into the segment directory.
-** This has the effect of flushing the segment's leaf data to
-** %_segments, and also flushing any interior nodes to %_segments.
-*/
-static int leafWriterFinalize(fulltext_vtab *v, LeafWriter *pWriter){
-  sqlite_int64 iEndBlockid;
-  char *pRootInfo;
-  int rc, nRootInfo;
-
-  rc = leafWriterRootInfo(v, pWriter, &pRootInfo, &nRootInfo, &iEndBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* Don't bother storing an entirely empty segment. */
-  if( iEndBlockid==0 && nRootInfo==0 ) return SQLITE_OK;
-
-  return segdir_set(v, pWriter->iLevel, pWriter->idx,
-                    pWriter->iStartBlockid, pWriter->iEndBlockid,
-                    iEndBlockid, pRootInfo, nRootInfo);
-}
-
-static void leafWriterDestroy(LeafWriter *pWriter){
-  if( pWriter->has_parent ) interiorWriterDestroy(&pWriter->parentWriter);
-  dataBufferDestroy(&pWriter->term);
-  dataBufferDestroy(&pWriter->data);
-}
-
-/* Encode a term into the leafWriter, delta-encoding as appropriate.
-** Returns the length of the new term which distinguishes it from the
-** previous term, which can be used to set nTermDistinct when a node
-** boundary is crossed.
-*/
-static int leafWriterEncodeTerm(LeafWriter *pWriter,
-                                const char *pTerm, int nTerm){
-  char c[VARINT_MAX+VARINT_MAX];
-  int n, nPrefix = 0;
-
-  assert( nTerm>0 );
-  while( nPrefix<pWriter->term.nData &&
-         pTerm[nPrefix]==pWriter->term.pData[nPrefix] ){
-    nPrefix++;
-    /* Failing this implies that the terms weren't in order. */
-    assert( nPrefix<nTerm );
-  }
-
-  if( pWriter->data.nData==0 ){
-    /* Encode the node header and leading term as:
-    **  varint(0)
-    **  varint(nTerm)
-    **  char pTerm[nTerm]
-    */
-    n = fts3PutVarint(c, '\0');
-    n += fts3PutVarint(c+n, nTerm);
-    dataBufferAppend2(&pWriter->data, c, n, pTerm, nTerm);
-  }else{
-    /* Delta-encode the term as:
-    **  varint(nPrefix)
-    **  varint(nSuffix)
-    **  char pTermSuffix[nSuffix]
-    */
-    n = fts3PutVarint(c, nPrefix);
-    n += fts3PutVarint(c+n, nTerm-nPrefix);
-    dataBufferAppend2(&pWriter->data, c, n, pTerm+nPrefix, nTerm-nPrefix);
-  }
-  dataBufferReplace(&pWriter->term, pTerm, nTerm);
-
-  return nPrefix+1;
-}
-
-/* Used to avoid a memmove when a large amount of doclist data is in
-** the buffer.  This constructs a node and term header before
-** iDoclistData and flushes the resulting complete node using
-** leafWriterInternalFlush().
-*/
-static int leafWriterInlineFlush(fulltext_vtab *v, LeafWriter *pWriter,
-                                 const char *pTerm, int nTerm,
-                                 int iDoclistData){
-  char c[VARINT_MAX+VARINT_MAX];
-  int iData, n = fts3PutVarint(c, 0);
-  n += fts3PutVarint(c+n, nTerm);
-
-  /* There should always be room for the header.  Even if pTerm shared
-  ** a substantial prefix with the previous term, the entire prefix
-  ** could be constructed from earlier data in the doclist, so there
-  ** should be room.
-  */
-  assert( iDoclistData>=n+nTerm );
-
-  iData = iDoclistData-(n+nTerm);
-  memcpy(pWriter->data.pData+iData, c, n);
-  memcpy(pWriter->data.pData+iData+n, pTerm, nTerm);
-
-  return leafWriterInternalFlush(v, pWriter, iData, pWriter->data.nData-iData);
-}
-
-/* Push pTerm[nTerm] along with the doclist data to the leaf layer of
-** %_segments.
-*/
-static int leafWriterStepMerge(fulltext_vtab *v, LeafWriter *pWriter,
-                               const char *pTerm, int nTerm,
-                               DLReader *pReaders, int nReaders){
-  char c[VARINT_MAX+VARINT_MAX];
-  int iTermData = pWriter->data.nData, iDoclistData;
-  int i, nData, n, nActualData, nActual, rc, nTermDistinct;
-
-  ASSERT_VALID_LEAF_NODE(pWriter->data.pData, pWriter->data.nData);
-  nTermDistinct = leafWriterEncodeTerm(pWriter, pTerm, nTerm);
-
-  /* Remember nTermDistinct if opening a new node. */
-  if( iTermData==0 ) pWriter->nTermDistinct = nTermDistinct;
-
-  iDoclistData = pWriter->data.nData;
-
-  /* Estimate the length of the merged doclist so we can leave space
-  ** to encode it.
-  */
-  for(i=0, nData=0; i<nReaders; i++){
-    nData += dlrAllDataBytes(&pReaders[i]);
-  }
-  n = fts3PutVarint(c, nData);
-  dataBufferAppend(&pWriter->data, c, n);
-
-  rc = docListMerge(&pWriter->data, pReaders, nReaders);
-  if( rc!=SQLITE_OK ) return rc;
-  ASSERT_VALID_DOCLIST(DL_DEFAULT,
-                       pWriter->data.pData+iDoclistData+n,
-                       pWriter->data.nData-iDoclistData-n, NULL);
-
-  /* The actual amount of doclist data at this point could be smaller
-  ** than the length we encoded.  Additionally, the space required to
-  ** encode this length could be smaller.  For small doclists, this is
-  ** not a big deal, we can just use memmove() to adjust things.
-  */
-  nActualData = pWriter->data.nData-(iDoclistData+n);
-  nActual = fts3PutVarint(c, nActualData);
-  assert( nActualData<=nData );
-  assert( nActual<=n );
-
-  /* If the new doclist is big enough for force a standalone leaf
-  ** node, we can immediately flush it inline without doing the
-  ** memmove().
-  */
-  /* TODO(shess) This test matches leafWriterStep(), which does this
-  ** test before it knows the cost to varint-encode the term and
-  ** doclist lengths.  At some point, change to
-  ** pWriter->data.nData-iTermData>STANDALONE_MIN.
-  */
-  if( nTerm+nActualData>STANDALONE_MIN ){
-    /* Push leaf node from before this term. */
-    if( iTermData>0 ){
-      rc = leafWriterInternalFlush(v, pWriter, 0, iTermData);
-      if( rc!=SQLITE_OK ) return rc;
-
-      pWriter->nTermDistinct = nTermDistinct;
-    }
-
-    /* Fix the encoded doclist length. */
-    iDoclistData += n - nActual;
-    memcpy(pWriter->data.pData+iDoclistData, c, nActual);
-
-    /* Push the standalone leaf node. */
-    rc = leafWriterInlineFlush(v, pWriter, pTerm, nTerm, iDoclistData);
-    if( rc!=SQLITE_OK ) return rc;
-
-    /* Leave the node empty. */
-    dataBufferReset(&pWriter->data);
-
-    return rc;
-  }
-
-  /* At this point, we know that the doclist was small, so do the
-  ** memmove if indicated.
-  */
-  if( nActual<n ){
-    memmove(pWriter->data.pData+iDoclistData+nActual,
-            pWriter->data.pData+iDoclistData+n,
-            pWriter->data.nData-(iDoclistData+n));
-    pWriter->data.nData -= n-nActual;
-  }
-
-  /* Replace written length with actual length. */
-  memcpy(pWriter->data.pData+iDoclistData, c, nActual);
-
-  /* If the node is too large, break things up. */
-  /* TODO(shess) This test matches leafWriterStep(), which does this
-  ** test before it knows the cost to varint-encode the term and
-  ** doclist lengths.  At some point, change to
-  ** pWriter->data.nData>LEAF_MAX.
-  */
-  if( iTermData+nTerm+nActualData>LEAF_MAX ){
-    /* Flush out the leading data as a node */
-    rc = leafWriterInternalFlush(v, pWriter, 0, iTermData);
-    if( rc!=SQLITE_OK ) return rc;
-
-    pWriter->nTermDistinct = nTermDistinct;
-
-    /* Rebuild header using the current term */
-    n = fts3PutVarint(pWriter->data.pData, 0);
-    n += fts3PutVarint(pWriter->data.pData+n, nTerm);
-    memcpy(pWriter->data.pData+n, pTerm, nTerm);
-    n += nTerm;
-
-    /* There should always be room, because the previous encoding
-    ** included all data necessary to construct the term.
-    */
-    assert( n<iDoclistData );
-    /* So long as STANDALONE_MIN is half or less of LEAF_MAX, the
-    ** following memcpy() is safe (as opposed to needing a memmove).
-    */
-    assert( 2*STANDALONE_MIN<=LEAF_MAX );
-    assert( n+pWriter->data.nData-iDoclistData<iDoclistData );
-    memcpy(pWriter->data.pData+n,
-           pWriter->data.pData+iDoclistData,
-           pWriter->data.nData-iDoclistData);
-    pWriter->data.nData -= iDoclistData-n;
-  }
-  ASSERT_VALID_LEAF_NODE(pWriter->data.pData, pWriter->data.nData);
-
-  return SQLITE_OK;
-}
-
-/* Push pTerm[nTerm] along with the doclist data to the leaf layer of
-** %_segments.
-*/
-/* TODO(shess) Revise writeZeroSegment() so that doclists are
-** constructed directly in pWriter->data.
-*/
-static int leafWriterStep(fulltext_vtab *v, LeafWriter *pWriter,
-                          const char *pTerm, int nTerm,
-                          const char *pData, int nData){
-  int rc;
-  DLReader reader;
-
-  rc = dlrInit(&reader, DL_DEFAULT, pData, nData);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = leafWriterStepMerge(v, pWriter, pTerm, nTerm, &reader, 1);
-  dlrDestroy(&reader);
-
-  return rc;
-}
-
-
-/****************************************************************/
-/* LeafReader is used to iterate over an individual leaf node. */
-typedef struct LeafReader {
-  DataBuffer term;          /* copy of current term. */
-
-  const char *pData;        /* data for current term. */
-  int nData;
-} LeafReader;
-
-static void leafReaderDestroy(LeafReader *pReader){
-  dataBufferDestroy(&pReader->term);
-  SCRAMBLE(pReader);
-}
-
-static int leafReaderAtEnd(LeafReader *pReader){
-  return pReader->nData<=0;
-}
-
-/* Access the current term. */
-static int leafReaderTermBytes(LeafReader *pReader){
-  return pReader->term.nData;
-}
-static const char *leafReaderTerm(LeafReader *pReader){
-  assert( pReader->term.nData>0 );
-  return pReader->term.pData;
-}
-
-/* Access the doclist data for the current term. */
-static int leafReaderDataBytes(LeafReader *pReader){
-  int nData;
-  assert( pReader->term.nData>0 );
-  fts3GetVarint32(pReader->pData, &nData);
-  return nData;
-}
-static const char *leafReaderData(LeafReader *pReader){
-  int n, nData;
-  assert( pReader->term.nData>0 );
-  n = fts3GetVarint32Safe(pReader->pData, &nData, pReader->nData);
-  if( !n || nData>pReader->nData-n ) return NULL;
-  return pReader->pData+n;
-}
-
-static int leafReaderInit(const char *pData, int nData,
-                          LeafReader *pReader){
-  int nTerm, n;
-
-  /* All callers check this precondition. */
-  assert( nData>0 );
-  assert( pData[0]=='\0' );
-
-  CLEAR(pReader);
-
-  /* Read the first term, skipping the header byte. */
-  n = fts3GetVarint32Safe(pData+1, &nTerm, nData-1);
-  if( !n || nTerm<0 || nTerm>nData-1-n ) return SQLITE_CORRUPT_BKPT;
-  dataBufferInit(&pReader->term, nTerm);
-  dataBufferReplace(&pReader->term, pData+1+n, nTerm);
-
-  /* Position after the first term. */
-  pReader->pData = pData+1+n+nTerm;
-  pReader->nData = nData-1-n-nTerm;
-  return SQLITE_OK;
-}
-
-/* Step the reader forward to the next term. */
-static int leafReaderStep(LeafReader *pReader){
-  int n, nData, nPrefix, nSuffix;
-  assert( !leafReaderAtEnd(pReader) );
-
-  /* Skip previous entry's data block. */
-  n = fts3GetVarint32Safe(pReader->pData, &nData, pReader->nData);
-  if( !n || nData<0 || nData>pReader->nData-n ) return SQLITE_CORRUPT_BKPT;
-  pReader->pData += n+nData;
-  pReader->nData -= n+nData;
-
-  if( !leafReaderAtEnd(pReader) ){
-    /* Construct the new term using a prefix from the old term plus a
-    ** suffix from the leaf data.
-    */
-    n = fts3GetVarint32Safe(pReader->pData, &nPrefix, pReader->nData);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    pReader->nData -= n;
-    pReader->pData += n;
-    n = fts3GetVarint32Safe(pReader->pData, &nSuffix, pReader->nData);
-    if( !n ) return SQLITE_CORRUPT_BKPT;
-    pReader->nData -= n;
-    pReader->pData += n;
-    if( nSuffix<0 || nSuffix>pReader->nData ) return SQLITE_CORRUPT_BKPT;
-    if( nPrefix<0 || nPrefix>pReader->term.nData ) return SQLITE_CORRUPT_BKPT;
-    pReader->term.nData = nPrefix;
-    dataBufferAppend(&pReader->term, pReader->pData, nSuffix);
-
-    pReader->pData += nSuffix;
-    pReader->nData -= nSuffix;
-  }
-  return SQLITE_OK;
-}
-
-/* strcmp-style comparison of pReader's current term against pTerm.
-** If isPrefix, equality means equal through nTerm bytes.
-*/
-static int leafReaderTermCmp(LeafReader *pReader,
-                             const char *pTerm, int nTerm, int isPrefix){
-  int c, n = pReader->term.nData<nTerm ? pReader->term.nData : nTerm;
-  if( n==0 ){
-    if( pReader->term.nData>0 ) return -1;
-    if(nTerm>0 ) return 1;
-    return 0;
-  }
-
-  c = memcmp(pReader->term.pData, pTerm, n);
-  if( c!=0 ) return c;
-  if( isPrefix && n==nTerm ) return 0;
-  return pReader->term.nData - nTerm;
-}
-
-
-/****************************************************************/
-/* LeavesReader wraps LeafReader to allow iterating over the entire
-** leaf layer of the tree.
-*/
-typedef struct LeavesReader {
-  int idx;                  /* Index within the segment. */
-
-  sqlite3_stmt *pStmt;      /* Statement we're streaming leaves from. */
-  int eof;                  /* we've seen SQLITE_DONE from pStmt. */
-
-  LeafReader leafReader;    /* reader for the current leaf. */
-  DataBuffer rootData;      /* root data for inline. */
-} LeavesReader;
-
-/* Access the current term. */
-static int leavesReaderTermBytes(LeavesReader *pReader){
-  assert( !pReader->eof );
-  return leafReaderTermBytes(&pReader->leafReader);
-}
-static const char *leavesReaderTerm(LeavesReader *pReader){
-  assert( !pReader->eof );
-  return leafReaderTerm(&pReader->leafReader);
-}
-
-/* Access the doclist data for the current term. */
-static int leavesReaderDataBytes(LeavesReader *pReader){
-  assert( !pReader->eof );
-  return leafReaderDataBytes(&pReader->leafReader);
-}
-static const char *leavesReaderData(LeavesReader *pReader){
-  assert( !pReader->eof );
-  return leafReaderData(&pReader->leafReader);
-}
-
-static int leavesReaderAtEnd(LeavesReader *pReader){
-  return pReader->eof;
-}
-
-/* loadSegmentLeaves() may not read all the way to SQLITE_DONE, thus
-** leaving the statement handle open, which locks the table.
-*/
-/* TODO(shess) This "solution" is not satisfactory.  Really, there
-** should be check-in function for all statement handles which
-** arranges to call sqlite3_reset().  This most likely will require
-** modification to control flow all over the place, though, so for now
-** just punt.
-**
-** Note the the current system assumes that segment merges will run to
-** completion, which is why this particular probably hasn't arisen in
-** this case.  Probably a brittle assumption.
-*/
-static int leavesReaderReset(LeavesReader *pReader){
-  return sqlite3_reset(pReader->pStmt);
-}
-
-static void leavesReaderDestroy(LeavesReader *pReader){
-  /* If idx is -1, that means we're using a non-cached statement
-  ** handle in the optimize() case, so we need to release it.
-  */
-  if( pReader->pStmt!=NULL && pReader->idx==-1 ){
-    sqlite3_finalize(pReader->pStmt);
-  }
-  leafReaderDestroy(&pReader->leafReader);
-  dataBufferDestroy(&pReader->rootData);
-  SCRAMBLE(pReader);
-}
-
-/* Initialize pReader with the given root data (if iStartBlockid==0
-** the leaf data was entirely contained in the root), or from the
-** stream of blocks between iStartBlockid and iEndBlockid, inclusive.
-*/
-static int leavesReaderInit(fulltext_vtab *v,
-                            int idx,
-                            sqlite_int64 iStartBlockid,
-                            sqlite_int64 iEndBlockid,
-                            const char *pRootData, int nRootData,
-                            LeavesReader *pReader){
-  CLEAR(pReader);
-  pReader->idx = idx;
-
-  dataBufferInit(&pReader->rootData, 0);
-  if( iStartBlockid==0 ){
-    int rc;
-    /* Corrupt if this can't be a leaf node. */
-    if( pRootData==NULL || nRootData<1 || pRootData[0]!='\0' ){
-      return SQLITE_CORRUPT_BKPT;
-    }
-    /* Entire leaf level fit in root data. */
-    dataBufferReplace(&pReader->rootData, pRootData, nRootData);
-    rc = leafReaderInit(pReader->rootData.pData, pReader->rootData.nData,
-                        &pReader->leafReader);
-    if( rc!=SQLITE_OK ){
-      dataBufferDestroy(&pReader->rootData);
-      return rc;
-    }
-  }else{
-    sqlite3_stmt *s;
-    int rc = sql_get_leaf_statement(v, idx, &s);
-    if( rc!=SQLITE_OK ) return rc;
-
-    rc = sqlite3_bind_int64(s, 1, iStartBlockid);
-    if( rc!=SQLITE_OK ) goto err;
-
-    rc = sqlite3_bind_int64(s, 2, iEndBlockid);
-    if( rc!=SQLITE_OK ) goto err;
-
-    rc = sqlite3_step(s);
-
-    /* Corrupt if interior node referenced missing leaf node. */
-    if( rc==SQLITE_DONE ){
-      rc = SQLITE_CORRUPT_BKPT;
-      goto err;
-    }
-
-    if( rc!=SQLITE_ROW ) goto err;
-    rc = SQLITE_OK;
-
-    /* Corrupt if leaf data isn't a blob. */
-    if( sqlite3_column_type(s, 0)!=SQLITE_BLOB ){
-      rc = SQLITE_CORRUPT_BKPT;
-    }else{
-      const char *pLeafData = sqlite3_column_blob(s, 0);
-      int nLeafData = sqlite3_column_bytes(s, 0);
-
-      /* Corrupt if this can't be a leaf node. */
-      if( pLeafData==NULL || nLeafData<1 || pLeafData[0]!='\0' ){
-        rc = SQLITE_CORRUPT_BKPT;
-      }else{
-        rc = leafReaderInit(pLeafData, nLeafData, &pReader->leafReader);
-      }
-    }
-
- err:
-    if( rc!=SQLITE_OK ){
-      if( idx==-1 ){
-        sqlite3_finalize(s);
-      }else{
-        sqlite3_reset(s);
-      }
-      return rc;
-    }
-
-    pReader->pStmt = s;
-  }
-  return SQLITE_OK;
-}
-
-/* Step the current leaf forward to the next term.  If we reach the
-** end of the current leaf, step forward to the next leaf block.
-*/
-static int leavesReaderStep(fulltext_vtab *v, LeavesReader *pReader){
-  int rc;
-  assert( !leavesReaderAtEnd(pReader) );
-  rc = leafReaderStep(&pReader->leafReader);
-  if( rc!=SQLITE_OK ) return rc;
-
-  if( leafReaderAtEnd(&pReader->leafReader) ){
-    if( pReader->rootData.pData ){
-      pReader->eof = 1;
-      return SQLITE_OK;
-    }
-    rc = sqlite3_step(pReader->pStmt);
-    if( rc!=SQLITE_ROW ){
-      pReader->eof = 1;
-      return rc==SQLITE_DONE ? SQLITE_OK : rc;
-    }
-
-    /* Corrupt if leaf data isn't a blob. */
-    if( sqlite3_column_type(pReader->pStmt, 0)!=SQLITE_BLOB ){
-      return SQLITE_CORRUPT_BKPT;
-    }else{
-      LeafReader tmp;
-      const char *pLeafData = sqlite3_column_blob(pReader->pStmt, 0);
-      int nLeafData = sqlite3_column_bytes(pReader->pStmt, 0);
-
-      /* Corrupt if this can't be a leaf node. */
-      if( pLeafData==NULL || nLeafData<1 || pLeafData[0]!='\0' ){
-        return SQLITE_CORRUPT_BKPT;
-      }
-
-      rc = leafReaderInit(pLeafData, nLeafData, &tmp);
-      if( rc!=SQLITE_OK ) return rc;
-      leafReaderDestroy(&pReader->leafReader);
-      pReader->leafReader = tmp;
-    }
-  }
-  return SQLITE_OK;
-}
-
-/* Order LeavesReaders by their term, ignoring idx.  Readers at eof
-** always sort to the end.
-*/
-static int leavesReaderTermCmp(LeavesReader *lr1, LeavesReader *lr2){
-  if( leavesReaderAtEnd(lr1) ){
-    if( leavesReaderAtEnd(lr2) ) return 0;
-    return 1;
-  }
-  if( leavesReaderAtEnd(lr2) ) return -1;
-
-  return leafReaderTermCmp(&lr1->leafReader,
-                           leavesReaderTerm(lr2), leavesReaderTermBytes(lr2),
-                           0);
-}
-
-/* Similar to leavesReaderTermCmp(), with additional ordering by idx
-** so that older segments sort before newer segments.
-*/
-static int leavesReaderCmp(LeavesReader *lr1, LeavesReader *lr2){
-  int c = leavesReaderTermCmp(lr1, lr2);
-  if( c!=0 ) return c;
-  return lr1->idx-lr2->idx;
-}
-
-/* Assume that pLr[1]..pLr[nLr] are sorted.  Bubble pLr[0] into its
-** sorted position.
-*/
-static void leavesReaderReorder(LeavesReader *pLr, int nLr){
-  while( nLr>1 && leavesReaderCmp(pLr, pLr+1)>0 ){
-    LeavesReader tmp = pLr[0];
-    pLr[0] = pLr[1];
-    pLr[1] = tmp;
-    nLr--;
-    pLr++;
-  }
-}
-
-/* Initializes pReaders with the segments from level iLevel, returning
-** the number of segments in *piReaders.  Leaves pReaders in sorted
-** order.
-*/
-static int leavesReadersInit(fulltext_vtab *v, int iLevel,
-                             LeavesReader *pReaders, int *piReaders){
-  sqlite3_stmt *s;
-  int i, rc = sql_get_statement(v, SEGDIR_SELECT_LEVEL_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int(s, 1, iLevel);
-  if( rc!=SQLITE_OK ) return rc;
-
-  i = 0;
-  while( (rc = sqlite3_step(s))==SQLITE_ROW ){
-    sqlite_int64 iStart = sqlite3_column_int64(s, 0);
-    sqlite_int64 iEnd = sqlite3_column_int64(s, 1);
-    const char *pRootData = sqlite3_column_blob(s, 2);
-    int nRootData = sqlite3_column_bytes(s, 2);
-    sqlite_int64 iIndex = sqlite3_column_int64(s, 3);
-
-    /* Corrupt if we get back different types than we stored. */
-    /* Also corrupt if the index is not sequential starting at 0. */
-    if( sqlite3_column_type(s, 0)!=SQLITE_INTEGER ||
-        sqlite3_column_type(s, 1)!=SQLITE_INTEGER ||
-        sqlite3_column_type(s, 2)!=SQLITE_BLOB ||
-        i!=iIndex ||
-        i>=MERGE_COUNT ){
-      rc = SQLITE_CORRUPT_BKPT;
-      break;
-    }
-
-    rc = leavesReaderInit(v, i, iStart, iEnd, pRootData, nRootData,
-                          &pReaders[i]);
-    if( rc!=SQLITE_OK ) break;
-
-    i++;
-  }
-  if( rc!=SQLITE_DONE ){
-    while( i-->0 ){
-      leavesReaderDestroy(&pReaders[i]);
-    }
-    sqlite3_reset(s);  /* So we don't leave a lock. */
-    return rc;
-  }
-
-  *piReaders = i;
-
-  /* Leave our results sorted by term, then age. */
-  while( i-- ){
-    leavesReaderReorder(pReaders+i, *piReaders-i);
-  }
-  return SQLITE_OK;
-}
-
-/* Merge doclists from pReaders[nReaders] into a single doclist, which
-** is written to pWriter.  Assumes pReaders is ordered oldest to
-** newest.
-*/
-/* TODO(shess) Consider putting this inline in segmentMerge(). */
-static int leavesReadersMerge(fulltext_vtab *v,
-                              LeavesReader *pReaders, int nReaders,
-                              LeafWriter *pWriter){
-  DLReader dlReaders[MERGE_COUNT];
-  const char *pTerm = leavesReaderTerm(pReaders);
-  int i, nTerm = leavesReaderTermBytes(pReaders);
-  int rc;
-
-  assert( nReaders<=MERGE_COUNT );
-
-  for(i=0; i<nReaders; i++){
-    const char *pData = leavesReaderData(pReaders+i);
-    if( pData==NULL ){
-      rc = SQLITE_CORRUPT_BKPT;
-      break;
-    }
-    rc = dlrInit(&dlReaders[i], DL_DEFAULT,
-                 pData,
-                 leavesReaderDataBytes(pReaders+i));
-    if( rc!=SQLITE_OK ) break;
-  }
-  if( rc!=SQLITE_OK ){
-    while( i-->0 ){
-      dlrDestroy(&dlReaders[i]);
-    }
-    return rc;
-  }
-
-  return leafWriterStepMerge(v, pWriter, pTerm, nTerm, dlReaders, nReaders);
-}
-
-/* Forward ref due to mutual recursion with segdirNextIndex(). */
-static int segmentMerge(fulltext_vtab *v, int iLevel);
-
-/* Put the next available index at iLevel into *pidx.  If iLevel
-** already has MERGE_COUNT segments, they are merged to a higher
-** level to make room.
-*/
-static int segdirNextIndex(fulltext_vtab *v, int iLevel, int *pidx){
-  int rc = segdir_max_index(v, iLevel, pidx);
-  if( rc==SQLITE_DONE ){              /* No segments at iLevel. */
-    *pidx = 0;
-  }else if( rc==SQLITE_ROW ){
-    if( *pidx==(MERGE_COUNT-1) ){
-      rc = segmentMerge(v, iLevel);
-      if( rc!=SQLITE_OK ) return rc;
-      *pidx = 0;
-    }else{
-      (*pidx)++;
-    }
-  }else{
-    return rc;
-  }
-  return SQLITE_OK;
-}
-
-/* Merge MERGE_COUNT segments at iLevel into a new segment at
-** iLevel+1.  If iLevel+1 is already full of segments, those will be
-** merged to make room.
-*/
-static int segmentMerge(fulltext_vtab *v, int iLevel){
-  LeafWriter writer;
-  LeavesReader lrs[MERGE_COUNT];
-  int i, rc, idx = 0;
-
-  /* Determine the next available segment index at the next level,
-  ** merging as necessary.
-  */
-  rc = segdirNextIndex(v, iLevel+1, &idx);
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* TODO(shess) This assumes that we'll always see exactly
-  ** MERGE_COUNT segments to merge at a given level.  That will be
-  ** broken if we allow the developer to request preemptive or
-  ** deferred merging.
-  */
-  memset(&lrs, '\0', sizeof(lrs));
-  rc = leavesReadersInit(v, iLevel, lrs, &i);
-  if( rc!=SQLITE_OK ) return rc;
-
-  leafWriterInit(iLevel+1, idx, &writer);
-
-  if( i!=MERGE_COUNT ){
-    rc = SQLITE_CORRUPT_BKPT;
-    goto err;
-  }
-
-  /* Since leavesReaderReorder() pushes readers at eof to the end,
-  ** when the first reader is empty, all will be empty.
-  */
-  while( !leavesReaderAtEnd(lrs) ){
-    /* Figure out how many readers share their next term. */
-    for(i=1; i<MERGE_COUNT && !leavesReaderAtEnd(lrs+i); i++){
-      if( 0!=leavesReaderTermCmp(lrs, lrs+i) ) break;
-    }
-
-    rc = leavesReadersMerge(v, lrs, i, &writer);
-    if( rc!=SQLITE_OK ) goto err;
-
-    /* Step forward those that were merged. */
-    while( i-->0 ){
-      rc = leavesReaderStep(v, lrs+i);
-      if( rc!=SQLITE_OK ) goto err;
-
-      /* Reorder by term, then by age. */
-      leavesReaderReorder(lrs+i, MERGE_COUNT-i);
-    }
-  }
-
-  for(i=0; i<MERGE_COUNT; i++){
-    leavesReaderDestroy(&lrs[i]);
-  }
-
-  rc = leafWriterFinalize(v, &writer);
-  leafWriterDestroy(&writer);
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* Delete the merged segment data. */
-  return segdir_delete(v, iLevel);
-
- err:
-  for(i=0; i<MERGE_COUNT; i++){
-    leavesReaderDestroy(&lrs[i]);
-  }
-  leafWriterDestroy(&writer);
-  return rc;
-}
-
-/* Accumulate the union of *acc and *pData into *acc. */
-static int docListAccumulateUnion(DataBuffer *acc,
-                                  const char *pData, int nData) {
-  DataBuffer tmp = *acc;
-  int rc;
-  dataBufferInit(acc, tmp.nData+nData);
-  rc = docListUnion(tmp.pData, tmp.nData, pData, nData, acc);
-  dataBufferDestroy(&tmp);
-  return rc;
-}
-
-/* TODO(shess) It might be interesting to explore different merge
-** strategies, here.  For instance, since this is a sorted merge, we
-** could easily merge many doclists in parallel.  With some
-** comprehension of the storage format, we could merge all of the
-** doclists within a leaf node directly from the leaf node's storage.
-** It may be worthwhile to merge smaller doclists before larger
-** doclists, since they can be traversed more quickly - but the
-** results may have less overlap, making them more expensive in a
-** different way.
-*/
-
-/* Scan pReader for pTerm/nTerm, and merge the term's doclist over
-** *out (any doclists with duplicate docids overwrite those in *out).
-** Internal function for loadSegmentLeaf().
-*/
-static int loadSegmentLeavesInt(fulltext_vtab *v, LeavesReader *pReader,
-                                const char *pTerm, int nTerm, int isPrefix,
-                                DataBuffer *out){
-  /* doclist data is accumulated into pBuffers similar to how one does
-  ** increment in binary arithmetic.  If index 0 is empty, the data is
-  ** stored there.  If there is data there, it is merged and the
-  ** results carried into position 1, with further merge-and-carry
-  ** until an empty position is found.
-  */
-  DataBuffer *pBuffers = NULL;
-  int nBuffers = 0, nMaxBuffers = 0, rc;
-
-  assert( nTerm>0 );
-
-  for(rc=SQLITE_OK; rc==SQLITE_OK && !leavesReaderAtEnd(pReader);
-      rc=leavesReaderStep(v, pReader)){
-    /* TODO(shess) Really want leavesReaderTermCmp(), but that name is
-    ** already taken to compare the terms of two LeavesReaders.  Think
-    ** on a better name.  [Meanwhile, break encapsulation rather than
-    ** use a confusing name.]
-    */
-    int c = leafReaderTermCmp(&pReader->leafReader, pTerm, nTerm, isPrefix);
-    if( c>0 ) break;      /* Past any possible matches. */
-    if( c==0 ){
-      int iBuffer, nData;
-      const char *pData = leavesReaderData(pReader);
-      if( pData==NULL ){
-        rc = SQLITE_CORRUPT_BKPT;
-        break;
-      }
-      nData = leavesReaderDataBytes(pReader);
-
-      /* Find the first empty buffer. */
-      for(iBuffer=0; iBuffer<nBuffers; ++iBuffer){
-        if( 0==pBuffers[iBuffer].nData ) break;
-      }
-
-      /* Out of buffers, add an empty one. */
-      if( iBuffer==nBuffers ){
-        if( nBuffers==nMaxBuffers ){
-          DataBuffer *p;
-          nMaxBuffers += 20;
-
-          /* Manual realloc so we can handle NULL appropriately. */
-          p = sqlite3_malloc(nMaxBuffers*sizeof(*pBuffers));
-          if( p==NULL ){
-            rc = SQLITE_NOMEM;
-            break;
-          }
-
-          if( nBuffers>0 ){
-            assert(pBuffers!=NULL);
-            memcpy(p, pBuffers, nBuffers*sizeof(*pBuffers));
-            sqlite3_free(pBuffers);
-          }
-          pBuffers = p;
-        }
-        dataBufferInit(&(pBuffers[nBuffers]), 0);
-        nBuffers++;
-      }
-
-      /* At this point, must have an empty at iBuffer. */
-      assert(iBuffer<nBuffers && pBuffers[iBuffer].nData==0);
-
-      /* If empty was first buffer, no need for merge logic. */
-      if( iBuffer==0 ){
-        dataBufferReplace(&(pBuffers[0]), pData, nData);
-      }else{
-        /* pAcc is the empty buffer the merged data will end up in. */
-        DataBuffer *pAcc = &(pBuffers[iBuffer]);
-        DataBuffer *p = &(pBuffers[0]);
-
-        /* Handle position 0 specially to avoid need to prime pAcc
-        ** with pData/nData.
-        */
-        dataBufferSwap(p, pAcc);
-        rc = docListAccumulateUnion(pAcc, pData, nData);
-        if( rc!=SQLITE_OK ) goto err;
-
-        /* Accumulate remaining doclists into pAcc. */
-        for(++p; p<pAcc; ++p){
-          rc = docListAccumulateUnion(pAcc, p->pData, p->nData);
-          if( rc!=SQLITE_OK ) goto err;
-
-          /* dataBufferReset() could allow a large doclist to blow up
-          ** our memory requirements.
-          */
-          if( p->nCapacity<1024 ){
-            dataBufferReset(p);
-          }else{
-            dataBufferDestroy(p);
-            dataBufferInit(p, 0);
-          }
-        }
-      }
-    }
-  }
-
-  /* Union all the doclists together into *out. */
-  /* TODO(shess) What if *out is big?  Sigh. */
-  if( rc==SQLITE_OK && nBuffers>0 ){
-    int iBuffer;
-    for(iBuffer=0; iBuffer<nBuffers; ++iBuffer){
-      if( pBuffers[iBuffer].nData>0 ){
-        if( out->nData==0 ){
-          dataBufferSwap(out, &(pBuffers[iBuffer]));
-        }else{
-          rc = docListAccumulateUnion(out, pBuffers[iBuffer].pData,
-                                      pBuffers[iBuffer].nData);
-          if( rc!=SQLITE_OK ) break;
-        }
-      }
-    }
-  }
-
-err:
-  while( nBuffers-- ){
-    dataBufferDestroy(&(pBuffers[nBuffers]));
-  }
-  if( pBuffers!=NULL ) sqlite3_free(pBuffers);
-
-  return rc;
-}
-
-/* Call loadSegmentLeavesInt() with pData/nData as input. */
-static int loadSegmentLeaf(fulltext_vtab *v, const char *pData, int nData,
-                           const char *pTerm, int nTerm, int isPrefix,
-                           DataBuffer *out){
-  LeavesReader reader;
-  int rc;
-
-  assert( nData>1 );
-  assert( *pData=='\0' );
-  rc = leavesReaderInit(v, 0, 0, 0, pData, nData, &reader);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = loadSegmentLeavesInt(v, &reader, pTerm, nTerm, isPrefix, out);
-  leavesReaderReset(&reader);
-  leavesReaderDestroy(&reader);
-  return rc;
-}
-
-/* Call loadSegmentLeavesInt() with the leaf nodes from iStartLeaf to
-** iEndLeaf (inclusive) as input, and merge the resulting doclist into
-** out.
-*/
-static int loadSegmentLeaves(fulltext_vtab *v,
-                             sqlite_int64 iStartLeaf, sqlite_int64 iEndLeaf,
-                             const char *pTerm, int nTerm, int isPrefix,
-                             DataBuffer *out){
-  int rc;
-  LeavesReader reader;
-
-  assert( iStartLeaf<=iEndLeaf );
-  rc = leavesReaderInit(v, 0, iStartLeaf, iEndLeaf, NULL, 0, &reader);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = loadSegmentLeavesInt(v, &reader, pTerm, nTerm, isPrefix, out);
-  leavesReaderReset(&reader);
-  leavesReaderDestroy(&reader);
-  return rc;
-}
-
-/* Taking pData/nData as an interior node, find the sequence of child
-** nodes which could include pTerm/nTerm/isPrefix.  Note that the
-** interior node terms logically come between the blocks, so there is
-** one more blockid than there are terms (that block contains terms >=
-** the last interior-node term).
-*/
-/* TODO(shess) The calling code may already know that the end child is
-** not worth calculating, because the end may be in a later sibling
-** node.  Consider whether breaking symmetry is worthwhile.  I suspect
-** it is not worthwhile.
-*/
-static int getChildrenContaining(const char *pData, int nData,
-                                 const char *pTerm, int nTerm, int isPrefix,
-                                 sqlite_int64 *piStartChild,
-                                 sqlite_int64 *piEndChild){
-  InteriorReader reader;
-  int rc;
-
-  assert( nData>1 );
-  assert( *pData!='\0' );
-  rc = interiorReaderInit(pData, nData, &reader);
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* Scan for the first child which could contain pTerm/nTerm. */
-  while( !interiorReaderAtEnd(&reader) ){
-    if( interiorReaderTermCmp(&reader, pTerm, nTerm, 0)>0 ) break;
-    rc = interiorReaderStep(&reader);
-    if( rc!=SQLITE_OK ){
-      interiorReaderDestroy(&reader);
-      return rc;
-    }
-  }
-  *piStartChild = interiorReaderCurrentBlockid(&reader);
-
-  /* Keep scanning to find a term greater than our term, using prefix
-  ** comparison if indicated.  If isPrefix is false, this will be the
-  ** same blockid as the starting block.
-  */
-  while( !interiorReaderAtEnd(&reader) ){
-    if( interiorReaderTermCmp(&reader, pTerm, nTerm, isPrefix)>0 ) break;
-    rc = interiorReaderStep(&reader);
-    if( rc!=SQLITE_OK ){
-      interiorReaderDestroy(&reader);
-      return rc;
-    }
-  }
-  *piEndChild = interiorReaderCurrentBlockid(&reader);
-
-  interiorReaderDestroy(&reader);
-
-  /* Children must ascend, and if !prefix, both must be the same. */
-  assert( *piEndChild>=*piStartChild );
-  assert( isPrefix || *piStartChild==*piEndChild );
-  return rc;
-}
-
-/* Read block at iBlockid and pass it with other params to
-** getChildrenContaining().
-*/
-static int loadAndGetChildrenContaining(
-  fulltext_vtab *v,
-  sqlite_int64 iBlockid,
-  const char *pTerm, int nTerm, int isPrefix,
-  sqlite_int64 *piStartChild, sqlite_int64 *piEndChild
-){
-  sqlite3_stmt *s = NULL;
-  int rc;
-
-  assert( iBlockid!=0 );
-  assert( pTerm!=NULL );
-  assert( nTerm!=0 );        /* TODO(shess) Why not allow this? */
-  assert( piStartChild!=NULL );
-  assert( piEndChild!=NULL );
-
-  rc = sql_get_statement(v, BLOCK_SELECT_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_bind_int64(s, 1, iBlockid);
-  if( rc!=SQLITE_OK ) return rc;
-
-  rc = sqlite3_step(s);
-  /* Corrupt if interior node references missing child node. */
-  if( rc==SQLITE_DONE ) return SQLITE_CORRUPT_BKPT;
-  if( rc!=SQLITE_ROW ) return rc;
-
-  /* Corrupt if child node isn't a blob. */
-  if( sqlite3_column_type(s, 0)!=SQLITE_BLOB ){
-    sqlite3_reset(s);  /* So we don't leave a lock. */
-    return SQLITE_CORRUPT_BKPT;
-  }else{
-    const char *pData = sqlite3_column_blob(s, 0);
-    int nData = sqlite3_column_bytes(s, 0);
-
-    /* Corrupt if child is not a valid interior node. */
-    if( pData==NULL || nData<1 || pData[0]=='\0' ){
-      sqlite3_reset(s);  /* So we don't leave a lock. */
-      return SQLITE_CORRUPT_BKPT;
-    }
-
-    rc = getChildrenContaining(pData, nData, pTerm, nTerm,
-                               isPrefix, piStartChild, piEndChild);
-    if( rc!=SQLITE_OK ){
-      sqlite3_reset(s);
-      return rc;
-    }
-  }
-
-  /* We expect only one row.  We must execute another sqlite3_step()
-   * to complete the iteration; otherwise the table will remain
-   * locked. */
-  rc = sqlite3_step(s);
-  if( rc==SQLITE_ROW ) return SQLITE_ERROR;
-  if( rc!=SQLITE_DONE ) return rc;
-
-  return SQLITE_OK;
-}
-
-/* Traverse the tree represented by pData[nData] looking for
-** pTerm[nTerm], placing its doclist into *out.  This is internal to
-** loadSegment() to make error-handling cleaner.
-*/
-static int loadSegmentInt(fulltext_vtab *v, const char *pData, int nData,
-                          sqlite_int64 iLeavesEnd,
-                          const char *pTerm, int nTerm, int isPrefix,
-                          DataBuffer *out){
-  /* Special case where root is a leaf. */
-  if( *pData=='\0' ){
-    return loadSegmentLeaf(v, pData, nData, pTerm, nTerm, isPrefix, out);
-  }else{
-    int rc;
-    sqlite_int64 iStartChild, iEndChild;
-
-    /* Process pData as an interior node, then loop down the tree
-    ** until we find the set of leaf nodes to scan for the term.
-    */
-    rc = getChildrenContaining(pData, nData, pTerm, nTerm, isPrefix,
-                               &iStartChild, &iEndChild);
-    if( rc!=SQLITE_OK ) return rc;
-    while( iStartChild>iLeavesEnd ){
-      sqlite_int64 iNextStart, iNextEnd;
-      rc = loadAndGetChildrenContaining(v, iStartChild, pTerm, nTerm, isPrefix,
-                                        &iNextStart, &iNextEnd);
-      if( rc!=SQLITE_OK ) return rc;
-
-      /* If we've branched, follow the end branch, too. */
-      if( iStartChild!=iEndChild ){
-        sqlite_int64 iDummy;
-        rc = loadAndGetChildrenContaining(v, iEndChild, pTerm, nTerm, isPrefix,
-                                          &iDummy, &iNextEnd);
-        if( rc!=SQLITE_OK ) return rc;
-      }
-
-      assert( iNextStart<=iNextEnd );
-      iStartChild = iNextStart;
-      iEndChild = iNextEnd;
-    }
-    assert( iStartChild<=iLeavesEnd );
-    assert( iEndChild<=iLeavesEnd );
-
-    /* Scan through the leaf segments for doclists. */
-    return loadSegmentLeaves(v, iStartChild, iEndChild,
-                             pTerm, nTerm, isPrefix, out);
-  }
-}
-
-/* Call loadSegmentInt() to collect the doclist for pTerm/nTerm, then
-** merge its doclist over *out (any duplicate doclists read from the
-** segment rooted at pData will overwrite those in *out).
-*/
-/* TODO(shess) Consider changing this to determine the depth of the
-** leaves using either the first characters of interior nodes (when
-** ==1, we're one level above the leaves), or the first character of
-** the root (which will describe the height of the tree directly).
-** Either feels somewhat tricky to me.
-*/
-/* TODO(shess) The current merge is likely to be slow for large
-** doclists (though it should process from newest/smallest to
-** oldest/largest, so it may not be that bad).  It might be useful to
-** modify things to allow for N-way merging.  This could either be
-** within a segment, with pairwise merges across segments, or across
-** all segments at once.
-*/
-static int loadSegment(fulltext_vtab *v, const char *pData, int nData,
-                       sqlite_int64 iLeavesEnd,
-                       const char *pTerm, int nTerm, int isPrefix,
-                       DataBuffer *out){
-  DataBuffer result;
-  int rc;
-
-  /* Corrupt if segment root can't be valid. */
-  if( pData==NULL || nData<1 ) return SQLITE_CORRUPT_BKPT;
-
-  /* This code should never be called with buffered updates. */
-  assert( v->nPendingData<0 );
-
-  dataBufferInit(&result, 0);
-  rc = loadSegmentInt(v, pData, nData, iLeavesEnd,
-                      pTerm, nTerm, isPrefix, &result);
-  if( rc==SQLITE_OK && result.nData>0 ){
-    if( out->nData==0 ){
-      DataBuffer tmp = *out;
-      *out = result;
-      result = tmp;
-    }else{
-      DataBuffer merged;
-      DLReader readers[2];
-
-      rc = dlrInit(&readers[0], DL_DEFAULT, out->pData, out->nData);
-      if( rc==SQLITE_OK ){
-        rc = dlrInit(&readers[1], DL_DEFAULT, result.pData, result.nData);
-        if( rc==SQLITE_OK ){
-          dataBufferInit(&merged, out->nData+result.nData);
-          rc = docListMerge(&merged, readers, 2);
-          dataBufferDestroy(out);
-          *out = merged;
-          dlrDestroy(&readers[1]);
-        }
-        dlrDestroy(&readers[0]);
-      }
-    }
-  }
-
-  dataBufferDestroy(&result);
-  return rc;
-}
-
-/* Scan the database and merge together the posting lists for the term
-** into *out.
-*/
-static int termSelect(
-  fulltext_vtab *v, 
-  int iColumn,
-  const char *pTerm, int nTerm,             /* Term to query for */
-  int isPrefix,                             /* True for a prefix search */
-  DocListType iType, 
-  DataBuffer *out                           /* Write results here */
-){
-  DataBuffer doclist;
-  sqlite3_stmt *s;
-  int rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
-  if( rc!=SQLITE_OK ) return rc;
-
-  /* This code should never be called with buffered updates. */
-  assert( v->nPendingData<0 );
-
-  dataBufferInit(&doclist, 0);
-  dataBufferInit(out, 0);
-
-  /* Traverse the segments from oldest to newest so that newer doclist
-  ** elements for given docids overwrite older elements.
-  */
-  while( (rc = sqlite3_step(s))==SQLITE_ROW ){
-    const char *pData = sqlite3_column_blob(s, 2);
-    const int nData = sqlite3_column_bytes(s, 2);
-    const sqlite_int64 iLeavesEnd = sqlite3_column_int64(s, 1);
-
-    /* Corrupt if we get back different types than we stored. */
-    if( sqlite3_column_type(s, 1)!=SQLITE_INTEGER ||
-        sqlite3_column_type(s, 2)!=SQLITE_BLOB ){
-      rc = SQLITE_CORRUPT_BKPT;
-      goto err;
-    }
-
-    rc = loadSegment(v, pData, nData, iLeavesEnd, pTerm, nTerm, isPrefix,
-                     &doclist);
-    if( rc!=SQLITE_OK ) goto err;
-  }
-  if( rc==SQLITE_DONE ){
-    rc = SQLITE_OK;
-    if( doclist.nData!=0 ){
-      /* TODO(shess) The old term_select_all() code applied the column
-      ** restrict as we merged segments, leading to smaller buffers.
-      ** This is probably worthwhile to bring back, once the new storage
-      ** system is checked in.
-      */
-      if( iColumn==v->nColumn) iColumn = -1;
-      rc = docListTrim(DL_DEFAULT, doclist.pData, doclist.nData,
-                       iColumn, iType, out);
-    }
-  }
-
- err:
-  sqlite3_reset(s);  /* So we don't leave a lock. */
-  dataBufferDestroy(&doclist);
-  return rc;
-}
-
-/****************************************************************/
-/* Used to hold hashtable data for sorting. */
-typedef struct TermData {
-  const char *pTerm;
-  int nTerm;
-  DLCollector *pCollector;
-} TermData;
-
-/* Orders TermData elements in strcmp fashion ( <0 for less-than, 0
-** for equal, >0 for greater-than).
-*/
-static int termDataCmp(const void *av, const void *bv){
-  const TermData *a = (const TermData *)av;
-  const TermData *b = (const TermData *)bv;
-  int n = a->nTerm<b->nTerm ? a->nTerm : b->nTerm;
-  int c = memcmp(a->pTerm, b->pTerm, n);
-  if( c!=0 ) return c;
-  return a->nTerm-b->nTerm;
-}
-
-/* Order pTerms data by term, then write a new level 0 segment using
-** LeafWriter.
-*/
-static int writeZeroSegment(fulltext_vtab *v, fts3Hash *pTerms){
-  fts3HashElem *e;
-  int idx, rc, i, n;
-  TermData *pData;
-  LeafWriter writer;
-  DataBuffer dl;
-
-  /* Determine the next index at level 0, merging as necessary. */
-  rc = segdirNextIndex(v, 0, &idx);
-  if( rc!=SQLITE_OK ) return rc;
-
-  n = fts3HashCount(pTerms);
-  pData = sqlite3_malloc(n*sizeof(TermData));
-
-  for(i = 0, e = fts3HashFirst(pTerms); e; i++, e = fts3HashNext(e)){
-    assert( i<n );
-    pData[i].pTerm = fts3HashKey(e);
-    pData[i].nTerm = fts3HashKeysize(e);
-    pData[i].pCollector = fts3HashData(e);
-  }
-  assert( i==n );
-
-  /* TODO(shess) Should we allow user-defined collation sequences,
-  ** here?  I think we only need that once we support prefix searches.
-  */
-  if( n>1 ) qsort(pData, n, sizeof(*pData), termDataCmp);
-
-  /* TODO(shess) Refactor so that we can write directly to the segment
-  ** DataBuffer, as happens for segment merges.
-  */
-  leafWriterInit(0, idx, &writer);
-  dataBufferInit(&dl, 0);
-  for(i=0; i<n; i++){
-    dataBufferReset(&dl);
-    dlcAddDoclist(pData[i].pCollector, &dl);
-    rc = leafWriterStep(v, &writer,
-                        pData[i].pTerm, pData[i].nTerm, dl.pData, dl.nData);
-    if( rc!=SQLITE_OK ) goto err;
-  }
-  rc = leafWriterFinalize(v, &writer);
-
- err:
-  dataBufferDestroy(&dl);
-  sqlite3_free(pData);
-  leafWriterDestroy(&writer);
-  return rc;
-}
-
-/* If pendingTerms has data, free it. */
-static int clearPendingTerms(fulltext_vtab *v){
-  if( v->nPendingData>=0 ){
-    fts3HashElem *e;
-    for(e=fts3HashFirst(&v->pendingTerms); e; e=fts3HashNext(e)){
-      dlcDelete(fts3HashData(e));
-    }
-    fts3HashClear(&v->pendingTerms);
-    v->nPendingData = -1;
-  }
-  return SQLITE_OK;
-}
-
-/* If pendingTerms has data, flush it to a level-zero segment, and
-** free it.
-*/
-static int flushPendingTerms(fulltext_vtab *v){
-  if( v->nPendingData>=0 ){
-    int rc = writeZeroSegment(v, &v->pendingTerms);
-    if( rc==SQLITE_OK ) clearPendingTerms(v);
-    return rc;
-  }
-  return SQLITE_OK;
-}
-
-/* If pendingTerms is "too big", or docid is out of order, flush it.
-** Regardless, be certain that pendingTerms is initialized for use.
-*/
-static int initPendingTerms(fulltext_vtab *v, sqlite_int64 iDocid){
-  /* TODO(shess) Explore whether partially flushing the buffer on
-  ** forced-flush would provide better performance.  I suspect that if
-  ** we ordered the doclists by size and flushed the largest until the
-  ** buffer was half empty, that would let the less frequent terms
-  ** generate longer doclists.
-  */
-  if( iDocid<=v->iPrevDocid || v->nPendingData>kPendingThreshold ){
-    int rc = flushPendingTerms(v);
-    if( rc!=SQLITE_OK ) return rc;
-  }
-  if( v->nPendingData<0 ){
-    fts3HashInit(&v->pendingTerms, FTS3_HASH_STRING, 1);
-    v->nPendingData = 0;
-  }
-  v->iPrevDocid = iDocid;
-  return SQLITE_OK;
-}
-
-/* This function implements the xUpdate callback; it is the top-level entry
- * point for inserting, deleting or updating a row in a full-text table. */
-static int fulltextUpdate(sqlite3_vtab *pVtab, int nArg, sqlite3_value **ppArg,
-                          sqlite_int64 *pRowid){
-  fulltext_vtab *v = (fulltext_vtab *) pVtab;
-  int rc;
-
-  FTSTRACE(("FTS3 Update %p\n", pVtab));
-
-  if( nArg<2 ){
-    rc = index_delete(v, sqlite3_value_int64(ppArg[0]));
-    if( rc==SQLITE_OK ){
-      /* If we just deleted the last row in the table, clear out the
-      ** index data.
-      */
-      rc = content_exists(v);
-      if( rc==SQLITE_ROW ){
-        rc = SQLITE_OK;
-      }else if( rc==SQLITE_DONE ){
-        /* Clear the pending terms so we don't flush a useless level-0
-        ** segment when the transaction closes.
-        */
-        rc = clearPendingTerms(v);
-        if( rc==SQLITE_OK ){
-          rc = segdir_delete_all(v);
-        }
-      }
-    }
-  } else if( sqlite3_value_type(ppArg[0]) != SQLITE_NULL ){
-    /* An update:
-     * ppArg[0] = old rowid
-     * ppArg[1] = new rowid
-     * ppArg[2..2+v->nColumn-1] = values
-     * ppArg[2+v->nColumn] = value for magic column (we ignore this)
-     * ppArg[2+v->nColumn+1] = value for docid
-     */
-    sqlite_int64 rowid = sqlite3_value_int64(ppArg[0]);
-    if( sqlite3_value_type(ppArg[1]) != SQLITE_INTEGER ||
-        sqlite3_value_int64(ppArg[1]) != rowid ){
-      rc = SQLITE_ERROR;  /* we don't allow changing the rowid */
-    }else if( sqlite3_value_type(ppArg[2+v->nColumn+1]) != SQLITE_INTEGER ||
-              sqlite3_value_int64(ppArg[2+v->nColumn+1]) != rowid ){
-      rc = SQLITE_ERROR;  /* we don't allow changing the docid */
-    }else{
-      assert( nArg==2+v->nColumn+2);
-      rc = index_update(v, rowid, &ppArg[2]);
-    }
-  } else {
-    /* An insert:
-     * ppArg[1] = requested rowid
-     * ppArg[2..2+v->nColumn-1] = values
-     * ppArg[2+v->nColumn] = value for magic column (we ignore this)
-     * ppArg[2+v->nColumn+1] = value for docid
-     */
-    sqlite3_value *pRequestDocid = ppArg[2+v->nColumn+1];
-    assert( nArg==2+v->nColumn+2);
-    if( SQLITE_NULL != sqlite3_value_type(pRequestDocid) &&
-        SQLITE_NULL != sqlite3_value_type(ppArg[1]) ){
-      /* TODO(shess) Consider allowing this to work if the values are
-      ** identical.  I'm inclined to discourage that usage, though,
-      ** given that both rowid and docid are special columns.  Better
-      ** would be to define one or the other as the default winner,
-      ** but should it be fts3-centric (docid) or SQLite-centric
-      ** (rowid)?
-      */
-      rc = SQLITE_ERROR;
-    }else{
-      if( SQLITE_NULL == sqlite3_value_type(pRequestDocid) ){
-        pRequestDocid = ppArg[1];
-      }
-      rc = index_insert(v, pRequestDocid, &ppArg[2], pRowid);
-    }
-  }
-
-  return rc;
-}
-
-static int fulltextSync(sqlite3_vtab *pVtab){
-  FTSTRACE(("FTS3 xSync()\n"));
-  return flushPendingTerms((fulltext_vtab *)pVtab);
-}
-
-static int fulltextBegin(sqlite3_vtab *pVtab){
-  fulltext_vtab *v = (fulltext_vtab *) pVtab;
-  FTSTRACE(("FTS3 xBegin()\n"));
-
-  /* Any buffered updates should have been cleared by the previous
-  ** transaction.
-  */
-  assert( v->nPendingData<0 );
-  return clearPendingTerms(v);
-}
-
-static int fulltextCommit(sqlite3_vtab *pVtab){
-  fulltext_vtab *v = (fulltext_vtab *) pVtab;
-  FTSTRACE(("FTS3 xCommit()\n"));
-
-  /* Buffered updates should have been cleared by fulltextSync(). */
-  assert( v->nPendingData<0 );
-  return clearPendingTerms(v);
-}
-
-static int fulltextRollback(sqlite3_vtab *pVtab){
-  FTSTRACE(("FTS3 xRollback()\n"));
-  return clearPendingTerms((fulltext_vtab *)pVtab);
-}
-
-/*
-** Implementation of the snippet() function for FTS3
-*/
-static void snippetFunc(
-  sqlite3_context *pContext,
-  int argc,
-  sqlite3_value **argv
-){
-  fulltext_cursor *pCursor;
-  if( argc<1 ) return;
-  if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
-      sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
-    sqlite3_result_error(pContext, "illegal first argument to html_snippet",-1);
-  }else{
-    const char *zStart = "<b>";
-    const char *zEnd = "</b>";
-    const char *zEllipsis = "<b>...</b>";
-    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
-    if( argc>=2 ){
-      zStart = (const char*)sqlite3_value_text(argv[1]);
-      if( argc>=3 ){
-        zEnd = (const char*)sqlite3_value_text(argv[2]);
-        if( argc>=4 ){
-          zEllipsis = (const char*)sqlite3_value_text(argv[3]);
-        }
-      }
-    }
-    snippetAllOffsets(pCursor);
-    snippetText(pCursor, zStart, zEnd, zEllipsis);
-    sqlite3_result_text(pContext, pCursor->snippet.zSnippet,
-                        pCursor->snippet.nSnippet, SQLITE_STATIC);
-  }
-}
-
-/*
-** Implementation of the offsets() function for FTS3
-*/
-static void snippetOffsetsFunc(
-  sqlite3_context *pContext,
-  int argc,
-  sqlite3_value **argv
-){
-  fulltext_cursor *pCursor;
-  if( argc<1 ) return;
-  if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
-      sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
-    sqlite3_result_error(pContext, "illegal first argument to offsets",-1);
-  }else{
-    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
-    snippetAllOffsets(pCursor);
-    snippetOffsetText(&pCursor->snippet);
-    sqlite3_result_text(pContext,
-                        pCursor->snippet.zOffset, pCursor->snippet.nOffset,
-                        SQLITE_STATIC);
-  }
-}
-
-/* OptLeavesReader is nearly identical to LeavesReader, except that
-** where LeavesReader is geared towards the merging of complete
-** segment levels (with exactly MERGE_COUNT segments), OptLeavesReader
-** is geared towards implementation of the optimize() function, and
-** can merge all segments simultaneously.  This version may be
-** somewhat less efficient than LeavesReader because it merges into an
-** accumulator rather than doing an N-way merge, but since segment
-** size grows exponentially (so segment count logrithmically) this is
-** probably not an immediate problem.
-*/
-/* TODO(shess): Prove that assertion, or extend the merge code to
-** merge tree fashion (like the prefix-searching code does).
-*/
-/* TODO(shess): OptLeavesReader and LeavesReader could probably be
-** merged with little or no loss of performance for LeavesReader.  The
-** merged code would need to handle >MERGE_COUNT segments, and would
-** also need to be able to optionally optimize away deletes.
-*/
-typedef struct OptLeavesReader {
-  /* Segment number, to order readers by age. */
-  int segment;
-  LeavesReader reader;
-} OptLeavesReader;
-
-static int optLeavesReaderAtEnd(OptLeavesReader *pReader){
-  return leavesReaderAtEnd(&pReader->reader);
-}
-static int optLeavesReaderTermBytes(OptLeavesReader *pReader){
-  return leavesReaderTermBytes(&pReader->reader);
-}
-static const char *optLeavesReaderData(OptLeavesReader *pReader){
-  return leavesReaderData(&pReader->reader);
-}
-static int optLeavesReaderDataBytes(OptLeavesReader *pReader){
-  return leavesReaderDataBytes(&pReader->reader);
-}
-static const char *optLeavesReaderTerm(OptLeavesReader *pReader){
-  return leavesReaderTerm(&pReader->reader);
-}
-static int optLeavesReaderStep(fulltext_vtab *v, OptLeavesReader *pReader){
-  return leavesReaderStep(v, &pReader->reader);
-}
-static int optLeavesReaderTermCmp(OptLeavesReader *lr1, OptLeavesReader *lr2){
-  return leavesReaderTermCmp(&lr1->reader, &lr2->reader);
-}
-/* Order by term ascending, segment ascending (oldest to newest), with
-** exhausted readers to the end.
-*/
-static int optLeavesReaderCmp(OptLeavesReader *lr1, OptLeavesReader *lr2){
-  int c = optLeavesReaderTermCmp(lr1, lr2);
-  if( c!=0 ) return c;
-  return lr1->segment-lr2->segment;
-}
-/* Bubble pLr[0] to appropriate place in pLr[1..nLr-1].  Assumes that
-** pLr[1..nLr-1] is already sorted.
-*/
-static void optLeavesReaderReorder(OptLeavesReader *pLr, int nLr){
-  while( nLr>1 && optLeavesReaderCmp(pLr, pLr+1)>0 ){
-    OptLeavesReader tmp = pLr[0];
-    pLr[0] = pLr[1];
-    pLr[1] = tmp;
-    nLr--;
-    pLr++;
-  }
-}
-
-/* optimize() helper function.  Put the readers in order and iterate
-** through them, merging doclists for matching terms into pWriter.
-** Returns SQLITE_OK on success, or the SQLite error code which
-** prevented success.
-*/
-static int optimizeInternal(fulltext_vtab *v,
-                            OptLeavesReader *readers, int nReaders,
-                            LeafWriter *pWriter){
-  int i, rc = SQLITE_OK;
-  DataBuffer doclist, merged, tmp;
-  const char *pData;
-
-  /* Order the readers. */
-  i = nReaders;
-  while( i-- > 0 ){
-    optLeavesReaderReorder(&readers[i], nReaders-i);
-  }
-
-  dataBufferInit(&doclist, LEAF_MAX);
-  dataBufferInit(&merged, LEAF_MAX);
-
-  /* Exhausted readers bubble to the end, so when the first reader is
-  ** at eof, all are at eof.
-  */
-  while( !optLeavesReaderAtEnd(&readers[0]) ){
-
-    /* Figure out how many readers share the next term. */
-    for(i=1; i<nReaders && !optLeavesReaderAtEnd(&readers[i]); i++){
-      if( 0!=optLeavesReaderTermCmp(&readers[0], &readers[i]) ) break;
-    }
-
-    pData = optLeavesReaderData(&readers[0]);
-    if( pData==NULL ){
-      rc = SQLITE_CORRUPT_BKPT;
-      break;
-    }
-
-    /* Special-case for no merge. */
-    if( i==1 ){
-      /* Trim deletions from the doclist. */
-      dataBufferReset(&merged);
-      rc = docListTrim(DL_DEFAULT, pData,
-                       optLeavesReaderDataBytes(&readers[0]),
-                       -1, DL_DEFAULT, &merged);
-      if( rc!=SQLITE_OK ) break;
-    }else{
-      DLReader dlReaders[MERGE_COUNT];
-      int iReader, nReaders;
-
-      /* Prime the pipeline with the first reader's doclist.  After
-      ** one pass index 0 will reference the accumulated doclist.
-      */
-      rc = dlrInit(&dlReaders[0], DL_DEFAULT,
-                   pData,
-                   optLeavesReaderDataBytes(&readers[0]));
-      if( rc!=SQLITE_OK ) break;
-      iReader = 1;
-
-      assert( iReader<i );  /* Must execute the loop at least once. */
-      while( iReader<i ){
-        /* Merge 16 inputs per pass. */
-        for( nReaders=1; iReader<i && nReaders<MERGE_COUNT;
-             iReader++, nReaders++ ){
-          pData = optLeavesReaderData(&readers[iReader]);
-          if( pData==NULL ){
-            rc = SQLITE_CORRUPT_BKPT;
-            break;
-          }
-          rc = dlrInit(&dlReaders[nReaders], DL_DEFAULT, pData,
-                       optLeavesReaderDataBytes(&readers[iReader]));
-          if( rc!=SQLITE_OK ) break;
-        }
-
-        /* Merge doclists and swap result into accumulator. */
-        if( rc==SQLITE_OK ){
-          dataBufferReset(&merged);
-          rc = docListMerge(&merged, dlReaders, nReaders);
-          tmp = merged;
-          merged = doclist;
-          doclist = tmp;
-        }
-
-        while( nReaders-- > 0 ){
-          dlrDestroy(&dlReaders[nReaders]);
-        }
-
-        if( rc!=SQLITE_OK ) goto err;
-
-        /* Accumulated doclist to reader 0 for next pass. */
-        rc = dlrInit(&dlReaders[0], DL_DEFAULT, doclist.pData, doclist.nData);
-        if( rc!=SQLITE_OK ) goto err;
-      }
-
-      /* Destroy reader that was left in the pipeline. */
-      dlrDestroy(&dlReaders[0]);
-
-      /* Trim deletions from the doclist. */
-      dataBufferReset(&merged);
-      rc = docListTrim(DL_DEFAULT, doclist.pData, doclist.nData,
-                       -1, DL_DEFAULT, &merged);
-      if( rc!=SQLITE_OK ) goto err;
-    }
-
-    /* Only pass doclists with hits (skip if all hits deleted). */
-    if( merged.nData>0 ){
-      rc = leafWriterStep(v, pWriter,
-                          optLeavesReaderTerm(&readers[0]),
-                          optLeavesReaderTermBytes(&readers[0]),
-                          merged.pData, merged.nData);
-      if( rc!=SQLITE_OK ) goto err;
-    }
-
-    /* Step merged readers to next term and reorder. */
-    while( i-- > 0 ){
-      rc = optLeavesReaderStep(v, &readers[i]);
-      if( rc!=SQLITE_OK ) goto err;
-
-      optLeavesReaderReorder(&readers[i], nReaders-i);
-    }
-  }
-
- err:
-  dataBufferDestroy(&doclist);
-  dataBufferDestroy(&merged);
-  return rc;
-}
-
-/* Implement optimize() function for FTS3.  optimize(t) merges all
-** segments in the fts index into a single segment.  't' is the magic
-** table-named column.
-*/
-static void optimizeFunc(sqlite3_context *pContext,
-                         int argc, sqlite3_value **argv){
-  fulltext_cursor *pCursor;
-  if( argc>1 ){
-    sqlite3_result_error(pContext, "excess arguments to optimize()",-1);
-  }else if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
-            sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
-    sqlite3_result_error(pContext, "illegal first argument to optimize",-1);
-  }else{
-    fulltext_vtab *v;
-    int i, rc, iMaxLevel;
-    OptLeavesReader *readers;
-    int nReaders;
-    LeafWriter writer;
-    sqlite3_stmt *s;
-
-    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
-    v = cursor_vtab(pCursor);
-
-    /* Flush any buffered updates before optimizing. */
-    rc = flushPendingTerms(v);
-    if( rc!=SQLITE_OK ) goto err;
-
-    rc = segdir_count(v, &nReaders, &iMaxLevel);
-    if( rc!=SQLITE_OK ) goto err;
-    if( nReaders==0 || nReaders==1 ){
-      sqlite3_result_text(pContext, "Index already optimal", -1,
-                          SQLITE_STATIC);
-      return;
-    }
-
-    rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
-    if( rc!=SQLITE_OK ) goto err;
-
-    readers = sqlite3_malloc(nReaders*sizeof(readers[0]));
-    if( readers==NULL ) goto err;
-
-    /* Note that there will already be a segment at this position
-    ** until we call segdir_delete() on iMaxLevel.
-    */
-    leafWriterInit(iMaxLevel, 0, &writer);
-
-    i = 0;
-    while( (rc = sqlite3_step(s))==SQLITE_ROW ){
-      sqlite_int64 iStart = sqlite3_column_int64(s, 0);
-      sqlite_int64 iEnd = sqlite3_column_int64(s, 1);
-      const char *pRootData = sqlite3_column_blob(s, 2);
-      int nRootData = sqlite3_column_bytes(s, 2);
-
-      /* Corrupt if we get back different types than we stored. */
-      if( sqlite3_column_type(s, 0)!=SQLITE_INTEGER ||
-          sqlite3_column_type(s, 1)!=SQLITE_INTEGER ||
-          sqlite3_column_type(s, 2)!=SQLITE_BLOB ){
-        rc = SQLITE_CORRUPT_BKPT;
-        break;
-      }
-
-      assert( i<nReaders );
-      rc = leavesReaderInit(v, -1, iStart, iEnd, pRootData, nRootData,
-                            &readers[i].reader);
-      if( rc!=SQLITE_OK ) break;
-
-      readers[i].segment = i;
-      i++;
-    }
-
-    /* If we managed to successfully read them all, optimize them. */
-    if( rc==SQLITE_DONE ){
-      assert( i==nReaders );
-      rc = optimizeInternal(v, readers, nReaders, &writer);
-    }else{
-      sqlite3_reset(s);  /* So we don't leave a lock. */
-    }
-
-    while( i-- > 0 ){
-      leavesReaderDestroy(&readers[i].reader);
-    }
-    sqlite3_free(readers);
-
-    /* If we've successfully gotten to here, delete the old segments
-    ** and flush the interior structure of the new segment.
-    */
-    if( rc==SQLITE_OK ){
-      for( i=0; i<=iMaxLevel; i++ ){
-        rc = segdir_delete(v, i);
-        if( rc!=SQLITE_OK ) break;
-      }
-
-      if( rc==SQLITE_OK ) rc = leafWriterFinalize(v, &writer);
-    }
-
-    leafWriterDestroy(&writer);
-
-    if( rc!=SQLITE_OK ) goto err;
-
-    sqlite3_result_text(pContext, "Index optimized", -1, SQLITE_STATIC);
-    return;
-
-    /* TODO(shess): Error-handling needs to be improved along the
-    ** lines of the dump_ functions.
-    */
- err:
-    {
-      char buf[512];
-      sqlite3_snprintf(sizeof(buf), buf, "Error in optimize: %s",
-                       sqlite3_errmsg(sqlite3_context_db_handle(pContext)));
-      sqlite3_result_error(pContext, buf, -1);
-    }
-  }
-}
-
-#ifdef SQLITE_TEST
-/* Generate an error of the form "<prefix>: <msg>".  If msg is NULL,
-** pull the error from the context's db handle.
-*/
-static void generateError(sqlite3_context *pContext,
-                          const char *prefix, const char *msg){
-  char buf[512];
-  if( msg==NULL ) msg = sqlite3_errmsg(sqlite3_context_db_handle(pContext));
-  sqlite3_snprintf(sizeof(buf), buf, "%s: %s", prefix, msg);
-  sqlite3_result_error(pContext, buf, -1);
-}
-
-/* Helper function to collect the set of terms in the segment into
-** pTerms.  The segment is defined by the leaf nodes between
-** iStartBlockid and iEndBlockid, inclusive, or by the contents of
-** pRootData if iStartBlockid is 0 (in which case the entire segment
-** fit in a leaf).
-*/
-static int collectSegmentTerms(fulltext_vtab *v, sqlite3_stmt *s,
-                               fts3Hash *pTerms){
-  const sqlite_int64 iStartBlockid = sqlite3_column_int64(s, 0);
-  const sqlite_int64 iEndBlockid = sqlite3_column_int64(s, 1);
-  const char *pRootData = sqlite3_column_blob(s, 2);
-  const int nRootData = sqlite3_column_bytes(s, 2);
-  int rc;
-  LeavesReader reader;
-
-  /* Corrupt if we get back different types than we stored. */
-  if( sqlite3_column_type(s, 0)!=SQLITE_INTEGER ||
-      sqlite3_column_type(s, 1)!=SQLITE_INTEGER ||
-      sqlite3_column_type(s, 2)!=SQLITE_BLOB ){
-    return SQLITE_CORRUPT_BKPT;
-  }
-
-  rc = leavesReaderInit(v, 0, iStartBlockid, iEndBlockid,
-                        pRootData, nRootData, &reader);
-  if( rc!=SQLITE_OK ) return rc;
-
-  while( rc==SQLITE_OK && !leavesReaderAtEnd(&reader) ){
-    const char *pTerm = leavesReaderTerm(&reader);
-    const int nTerm = leavesReaderTermBytes(&reader);
-    void *oldValue = sqlite3Fts3HashFind(pTerms, pTerm, nTerm);
-    void *newValue = (void *)((char *)oldValue+1);
-
-    /* From the comment before sqlite3Fts3HashInsert in fts3_hash.c,
-    ** the data value passed is returned in case of malloc failure.
-    */
-    if( newValue==sqlite3Fts3HashInsert(pTerms, pTerm, nTerm, newValue) ){
-      rc = SQLITE_NOMEM;
-    }else{
-      rc = leavesReaderStep(v, &reader);
-    }
-  }
-
-  leavesReaderDestroy(&reader);
-  return rc;
-}
-
-/* Helper function to build the result string for dump_terms(). */
-static int generateTermsResult(sqlite3_context *pContext, fts3Hash *pTerms){
-  int iTerm, nTerms, nResultBytes, iByte;
-  char *result;
-  TermData *pData;
-  fts3HashElem *e;
-
-  /* Iterate pTerms to generate an array of terms in pData for
-  ** sorting.
-  */
-  nTerms = fts3HashCount(pTerms);
-  assert( nTerms>0 );
-  pData = sqlite3_malloc(nTerms*sizeof(TermData));
-  if( pData==NULL ) return SQLITE_NOMEM;
-
-  nResultBytes = 0;
-  for(iTerm = 0, e = fts3HashFirst(pTerms); e; iTerm++, e = fts3HashNext(e)){
-    nResultBytes += fts3HashKeysize(e)+1;   /* Term plus trailing space */
-    assert( iTerm<nTerms );
-    pData[iTerm].pTerm = fts3HashKey(e);
-    pData[iTerm].nTerm = fts3HashKeysize(e);
-    pData[iTerm].pCollector = fts3HashData(e);  /* unused */
-  }
-  assert( iTerm==nTerms );
-
-  assert( nResultBytes>0 );   /* nTerms>0, nResultsBytes must be, too. */
-  result = sqlite3_malloc(nResultBytes);
-  if( result==NULL ){
-    sqlite3_free(pData);
-    return SQLITE_NOMEM;
-  }
-
-  if( nTerms>1 ) qsort(pData, nTerms, sizeof(*pData), termDataCmp);
-
-  /* Read the terms in order to build the result. */
-  iByte = 0;
-  for(iTerm=0; iTerm<nTerms; ++iTerm){
-    memcpy(result+iByte, pData[iTerm].pTerm, pData[iTerm].nTerm);
-    iByte += pData[iTerm].nTerm;
-    result[iByte++] = ' ';
-  }
-  assert( iByte==nResultBytes );
-  assert( result[nResultBytes-1]==' ' );
-  result[nResultBytes-1] = '\0';
-
-  /* Passes away ownership of result. */
-  sqlite3_result_text(pContext, result, nResultBytes-1, sqlite3_free);
-  sqlite3_free(pData);
-  return SQLITE_OK;
-}
-
-/* Implements dump_terms() for use in inspecting the fts3 index from
-** tests.  TEXT result containing the ordered list of terms joined by
-** spaces.  dump_terms(t, level, idx) dumps the terms for the segment
-** specified by level, idx (in %_segdir), while dump_terms(t) dumps
-** all terms in the index.  In both cases t is the fts table's magic
-** table-named column.
-*/
-static void dumpTermsFunc(
-  sqlite3_context *pContext,
-  int argc, sqlite3_value **argv
-){
-  fulltext_cursor *pCursor;
-  if( argc!=3 && argc!=1 ){
-    generateError(pContext, "dump_terms", "incorrect arguments");
-  }else if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
-            sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
-    generateError(pContext, "dump_terms", "illegal first argument");
-  }else{
-    fulltext_vtab *v;
-    fts3Hash terms;
-    sqlite3_stmt *s = NULL;
-    int rc;
-
-    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
-    v = cursor_vtab(pCursor);
-
-    /* If passed only the cursor column, get all segments.  Otherwise
-    ** get the segment described by the following two arguments.
-    */
-    if( argc==1 ){
-      rc = sql_get_statement(v, SEGDIR_SELECT_ALL_STMT, &s);
-    }else{
-      rc = sql_get_statement(v, SEGDIR_SELECT_SEGMENT_STMT, &s);
-      if( rc==SQLITE_OK ){
-        rc = sqlite3_bind_int(s, 1, sqlite3_value_int(argv[1]));
-        if( rc==SQLITE_OK ){
-          rc = sqlite3_bind_int(s, 2, sqlite3_value_int(argv[2]));
-        }
-      }
-    }
-
-    if( rc!=SQLITE_OK ){
-      generateError(pContext, "dump_terms", NULL);
-      return;
-    }
-
-    /* Collect the terms for each segment. */
-    sqlite3Fts3HashInit(&terms, FTS3_HASH_STRING, 1);
-    while( (rc = sqlite3_step(s))==SQLITE_ROW ){
-      rc = collectSegmentTerms(v, s, &terms);
-      if( rc!=SQLITE_OK ) break;
-    }
-
-    if( rc!=SQLITE_DONE ){
-      sqlite3_reset(s);
-      generateError(pContext, "dump_terms", NULL);
-    }else{
-      const int nTerms = fts3HashCount(&terms);
-      if( nTerms>0 ){
-        rc = generateTermsResult(pContext, &terms);
-        if( rc==SQLITE_NOMEM ){
-          generateError(pContext, "dump_terms", "out of memory");
-        }else{
-          assert( rc==SQLITE_OK );
-        }
-      }else if( argc==3 ){
-        /* The specific segment asked for could not be found. */
-        generateError(pContext, "dump_terms", "segment not found");
-      }else{
-        /* No segments found. */
-        /* TODO(shess): It should be impossible to reach this.  This
-        ** case can only happen for an empty table, in which case
-        ** SQLite has no rows to call this function on.
-        */
-        sqlite3_result_null(pContext);
-      }
-    }
-    sqlite3Fts3HashClear(&terms);
-  }
-}
-
-/* Expand the DL_DEFAULT doclist in pData into a text result in
-** pContext.
-*/
-static void createDoclistResult(sqlite3_context *pContext,
-                                const char *pData, int nData){
-  DataBuffer dump;
-  DLReader dlReader;
-  int rc;
-
-  assert( pData!=NULL && nData>0 );
-
-  rc = dlrInit(&dlReader, DL_DEFAULT, pData, nData);
-  if( rc!=SQLITE_OK ) return rc;
-  dataBufferInit(&dump, 0);
-  for( ; rc==SQLITE_OK && !dlrAtEnd(&dlReader); rc = dlrStep(&dlReader) ){
-    char buf[256];
-    PLReader plReader;
-
-    rc = plrInit(&plReader, &dlReader);
-    if( rc!=SQLITE_OK ) break;
-    if( DL_DEFAULT==DL_DOCIDS || plrAtEnd(&plReader) ){
-      sqlite3_snprintf(sizeof(buf), buf, "[%lld] ", dlrDocid(&dlReader));
-      dataBufferAppend(&dump, buf, strlen(buf));
-    }else{
-      int iColumn = plrColumn(&plReader);
-
-      sqlite3_snprintf(sizeof(buf), buf, "[%lld %d[",
-                       dlrDocid(&dlReader), iColumn);
-      dataBufferAppend(&dump, buf, strlen(buf));
-
-      for( ; !plrAtEnd(&plReader); rc = plrStep(&plReader) ){
-        if( rc!=SQLITE_OK ) break;
-        if( plrColumn(&plReader)!=iColumn ){
-          iColumn = plrColumn(&plReader);
-          sqlite3_snprintf(sizeof(buf), buf, "] %d[", iColumn);
-          assert( dump.nData>0 );
-          dump.nData--;                     /* Overwrite trailing space. */
-          assert( dump.pData[dump.nData]==' ');
-          dataBufferAppend(&dump, buf, strlen(buf));
-        }
-        if( DL_DEFAULT==DL_POSITIONS_OFFSETS ){
-          sqlite3_snprintf(sizeof(buf), buf, "%d,%d,%d ",
-                           plrPosition(&plReader),
-                           plrStartOffset(&plReader), plrEndOffset(&plReader));
-        }else if( DL_DEFAULT==DL_POSITIONS ){
-          sqlite3_snprintf(sizeof(buf), buf, "%d ", plrPosition(&plReader));
-        }else{
-          assert( NULL=="Unhandled DL_DEFAULT value");
-        }
-        dataBufferAppend(&dump, buf, strlen(buf));
-      }
-      plrDestroy(&plReader);
-      if( rc!= SQLITE_OK ) break;
-
-      assert( dump.nData>0 );
-      dump.nData--;                     /* Overwrite trailing space. */
-      assert( dump.pData[dump.nData]==' ');
-      dataBufferAppend(&dump, "]] ", 3);
-    }
-  }
-  dlrDestroy(&dlReader);
-  if( rc!=SQLITE_OK ){
-    dataBufferDestroy(&dump);
-    return rc;
-  }
-
-  assert( dump.nData>0 );
-  dump.nData--;                     /* Overwrite trailing space. */
-  assert( dump.pData[dump.nData]==' ');
-  dump.pData[dump.nData] = '\0';
-  assert( dump.nData>0 );
-
-  /* Passes ownership of dump's buffer to pContext. */
-  sqlite3_result_text(pContext, dump.pData, dump.nData, sqlite3_free);
-  dump.pData = NULL;
-  dump.nData = dump.nCapacity = 0;
-  return SQLITE_OK;
-}
-
-/* Implements dump_doclist() for use in inspecting the fts3 index from
-** tests.  TEXT result containing a string representation of the
-** doclist for the indicated term.  dump_doclist(t, term, level, idx)
-** dumps the doclist for term from the segment specified by level, idx
-** (in %_segdir), while dump_doclist(t, term) dumps the logical
-** doclist for the term across all segments.  The per-segment doclist
-** can contain deletions, while the full-index doclist will not
-** (deletions are omitted).
-**
-** Result formats differ with the setting of DL_DEFAULTS.  Examples:
-**
-** DL_DOCIDS: [1] [3] [7]
-** DL_POSITIONS: [1 0[0 4] 1[17]] [3 1[5]]
-** DL_POSITIONS_OFFSETS: [1 0[0,0,3 4,23,26] 1[17,102,105]] [3 1[5,20,23]]
-**
-** In each case the number after the outer '[' is the docid.  In the
-** latter two cases, the number before the inner '[' is the column
-** associated with the values within.  For DL_POSITIONS the numbers
-** within are the positions, for DL_POSITIONS_OFFSETS they are the
-** position, the start offset, and the end offset.
-*/
-static void dumpDoclistFunc(
-  sqlite3_context *pContext,
-  int argc, sqlite3_value **argv
-){
-  fulltext_cursor *pCursor;
-  if( argc!=2 && argc!=4 ){
-    generateError(pContext, "dump_doclist", "incorrect arguments");
-  }else if( sqlite3_value_type(argv[0])!=SQLITE_BLOB ||
-            sqlite3_value_bytes(argv[0])!=sizeof(pCursor) ){
-    generateError(pContext, "dump_doclist", "illegal first argument");
-  }else if( sqlite3_value_text(argv[1])==NULL ||
-            sqlite3_value_text(argv[1])[0]=='\0' ){
-    generateError(pContext, "dump_doclist", "empty second argument");
-  }else{
-    const char *pTerm = (const char *)sqlite3_value_text(argv[1]);
-    const int nTerm = strlen(pTerm);
-    fulltext_vtab *v;
-    int rc;
-    DataBuffer doclist;
-
-    memcpy(&pCursor, sqlite3_value_blob(argv[0]), sizeof(pCursor));
-    v = cursor_vtab(pCursor);
-
-    dataBufferInit(&doclist, 0);
-
-    /* termSelect() yields the same logical doclist that queries are
-    ** run against.
-    */
-    if( argc==2 ){
-      rc = termSelect(v, v->nColumn, pTerm, nTerm, 0, DL_DEFAULT, &doclist);
-    }else{
-      sqlite3_stmt *s = NULL;
-
-      /* Get our specific segment's information. */
-      rc = sql_get_statement(v, SEGDIR_SELECT_SEGMENT_STMT, &s);
-      if( rc==SQLITE_OK ){
-        rc = sqlite3_bind_int(s, 1, sqlite3_value_int(argv[2]));
-        if( rc==SQLITE_OK ){
-          rc = sqlite3_bind_int(s, 2, sqlite3_value_int(argv[3]));
-        }
-      }
-
-      if( rc==SQLITE_OK ){
-        rc = sqlite3_step(s);
-
-        if( rc==SQLITE_DONE ){
-          dataBufferDestroy(&doclist);
-          generateError(pContext, "dump_doclist", "segment not found");
-          return;
-        }
-
-        /* Found a segment, load it into doclist. */
-        if( rc==SQLITE_ROW ){
-          const sqlite_int64 iLeavesEnd = sqlite3_column_int64(s, 1);
-          const char *pData = sqlite3_column_blob(s, 2);
-          const int nData = sqlite3_column_bytes(s, 2);
-
-          /* loadSegment() is used by termSelect() to load each
-          ** segment's data.
-          */
-          rc = loadSegment(v, pData, nData, iLeavesEnd, pTerm, nTerm, 0,
-                           &doclist);
-          if( rc==SQLITE_OK ){
-            rc = sqlite3_step(s);
-
-            /* Should not have more than one matching segment. */
-            if( rc!=SQLITE_DONE ){
-              sqlite3_reset(s);
-              dataBufferDestroy(&doclist);
-              generateError(pContext, "dump_doclist", "invalid segdir");
-              return;
-            }
-            rc = SQLITE_OK;
-          }
-        }
-      }
-
-      sqlite3_reset(s);
-    }
-
-    if( rc==SQLITE_OK ){
-      if( doclist.nData>0 ){
-        createDoclistResult(pContext, doclist.pData, doclist.nData);
-      }else{
-        /* TODO(shess): This can happen if the term is not present, or
-        ** if all instances of the term have been deleted and this is
-        ** an all-index dump.  It may be interesting to distinguish
-        ** these cases.
-        */
-        sqlite3_result_text(pContext, "", 0, SQLITE_STATIC);
-      }
-    }else if( rc==SQLITE_NOMEM ){
-      /* Handle out-of-memory cases specially because if they are
-      ** generated in fts3 code they may not be reflected in the db
-      ** handle.
-      */
-      /* TODO(shess): Handle this more comprehensively.
-      ** sqlite3ErrStr() has what I need, but is internal.
-      */
-      generateError(pContext, "dump_doclist", "out of memory");
-    }else{
-      generateError(pContext, "dump_doclist", NULL);
-    }
-
-    dataBufferDestroy(&doclist);
-  }
-}
-#endif
+  }
+}
+
+/*
+** Implementation of the matchinfo() function for FTS3
+*/
+static void fts3MatchinfoFunc(
+  sqlite3_context *pContext,      /* SQLite function call context */
+  int nVal,                       /* Size of argument array */
+  sqlite3_value **apVal           /* Array of arguments */
+){
+  Fts3Cursor *pCsr;               /* Cursor handle passed through apVal[0] */
+  assert( nVal==1 || nVal==2 );
+  if( SQLITE_OK==fts3FunctionArg(pContext, "matchinfo", apVal[0], &pCsr) ){
+    const char *zArg = 0;
+    if( nVal>1 ){
+      zArg = (const char *)sqlite3_value_text(apVal[1]);
+    }
+    sqlite3Fts3Matchinfo(pContext, pCsr, zArg);
+  }
+}
 
 /*
 ** This routine implements the xFindFunction method for the FTS3
 ** virtual table.
 */
-static int fulltextFindFunction(
-  sqlite3_vtab *pVtab,
-  int nArg,
-  const char *zName,
-  void (**pxFunc)(sqlite3_context*,int,sqlite3_value**),
-  void **ppArg
-){
-  if( strcmp(zName,"snippet")==0 ){
-    *pxFunc = snippetFunc;
-    return 1;
-  }else if( strcmp(zName,"offsets")==0 ){
-    *pxFunc = snippetOffsetsFunc;
-    return 1;
-  }else if( strcmp(zName,"optimize")==0 ){
-    *pxFunc = optimizeFunc;
-    return 1;
-#ifdef SQLITE_TEST
-    /* NOTE(shess): These functions are present only for testing
-    ** purposes.  No particular effort is made to optimize their
-    ** execution or how they build their results.
-    */
-  }else if( strcmp(zName,"dump_terms")==0 ){
-    /* fprintf(stderr, "Found dump_terms\n"); */
-    *pxFunc = dumpTermsFunc;
-    return 1;
-  }else if( strcmp(zName,"dump_doclist")==0 ){
-    /* fprintf(stderr, "Found dump_doclist\n"); */
-    *pxFunc = dumpDoclistFunc;
-    return 1;
-#endif
-  }
+static int fts3FindFunctionMethod(
+  sqlite3_vtab *pVtab,            /* Virtual table handle */
+  int nArg,                       /* Number of SQL function arguments */
+  const char *zName,              /* Name of SQL function */
+  void (**pxFunc)(sqlite3_context*,int,sqlite3_value**), /* OUT: Result */
+  void **ppArg                    /* Unused */
+){
+  struct Overloaded {
+    const char *zName;
+    void (*xFunc)(sqlite3_context*,int,sqlite3_value**);
+  } aOverload[] = {
+    { "snippet", fts3SnippetFunc },
+    { "offsets", fts3OffsetsFunc },
+    { "optimize", fts3OptimizeFunc },
+    { "matchinfo", fts3MatchinfoFunc },
+  };
+  int i;                          /* Iterator variable */
+
+  UNUSED_PARAMETER(pVtab);
+  UNUSED_PARAMETER(nArg);
+  UNUSED_PARAMETER(ppArg);
+
+  for(i=0; i<SizeofArray(aOverload); i++){
+    if( strcmp(zName, aOverload[i].zName)==0 ){
+      *pxFunc = aOverload[i].xFunc;
+      return 1;
+    }
+  }
+
+  /* No function of the specified name was found. Return 0. */
   return 0;
 }
 
 /*
-** Rename an fts3 table.
-*/
-static int fulltextRename(
-  sqlite3_vtab *pVtab,
-  const char *zName
-){
-  fulltext_vtab *p = (fulltext_vtab *)pVtab;
-  int rc = SQLITE_NOMEM;
-  char *zSql = sqlite3_mprintf(
-    "ALTER TABLE %Q.'%q_content'  RENAME TO '%q_content';"
-    "ALTER TABLE %Q.'%q_segments' RENAME TO '%q_segments';"
-    "ALTER TABLE %Q.'%q_segdir'   RENAME TO '%q_segdir';"
-    , p->zDb, p->zName, zName 
-    , p->zDb, p->zName, zName 
-    , p->zDb, p->zName, zName
+** Implementation of FTS3 xRename method. Rename an fts3 table.
+*/
+static int fts3RenameMethod(
+  sqlite3_vtab *pVtab,            /* Virtual table handle */
+  const char *zName               /* New name of table */
+){
+  Fts3Table *p = (Fts3Table *)pVtab;
+  sqlite3 *db = p->db;            /* Database connection */
+  int rc;                         /* Return Code */
+
+  rc = sqlite3Fts3PendingTermsFlush(p);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  fts3DbExec(&rc, db,
+    "ALTER TABLE %Q.'%q_content'  RENAME TO '%q_content';",
+    p->zDb, p->zName, zName
   );
-  if( zSql ){
-    rc = sqlite3_exec(p->db, zSql, 0, 0, 0);
-    sqlite3_free(zSql);
-  }
+  if( p->bHasDocsize ){
+    fts3DbExec(&rc, db,
+      "ALTER TABLE %Q.'%q_docsize'  RENAME TO '%q_docsize';",
+      p->zDb, p->zName, zName
+    );
+  }
+  if( p->bHasStat ){
+    fts3DbExec(&rc, db,
+      "ALTER TABLE %Q.'%q_stat'  RENAME TO '%q_stat';",
+      p->zDb, p->zName, zName
+    );
+  }
+  fts3DbExec(&rc, db,
+    "ALTER TABLE %Q.'%q_segments' RENAME TO '%q_segments';",
+    p->zDb, p->zName, zName
+  );
+  fts3DbExec(&rc, db,
+    "ALTER TABLE %Q.'%q_segdir'   RENAME TO '%q_segdir';",
+    p->zDb, p->zName, zName
+  );
   return rc;
 }
 
 static const sqlite3_module fts3Module = {
   /* iVersion      */ 0,
-  /* xCreate       */ fulltextCreate,
-  /* xConnect      */ fulltextConnect,
-  /* xBestIndex    */ fulltextBestIndex,
-  /* xDisconnect   */ fulltextDisconnect,
-  /* xDestroy      */ fulltextDestroy,
-  /* xOpen         */ fulltextOpen,
-  /* xClose        */ fulltextClose,
-  /* xFilter       */ fulltextFilter,
-  /* xNext         */ fulltextNext,
-  /* xEof          */ fulltextEof,
-  /* xColumn       */ fulltextColumn,
-  /* xRowid        */ fulltextRowid,
-  /* xUpdate       */ fulltextUpdate,
-  /* xBegin        */ fulltextBegin,
-  /* xSync         */ fulltextSync,
-  /* xCommit       */ fulltextCommit,
-  /* xRollback     */ fulltextRollback,
-  /* xFindFunction */ fulltextFindFunction,
-  /* xRename */       fulltextRename,
+  /* xCreate       */ fts3CreateMethod,
+  /* xConnect      */ fts3ConnectMethod,
+  /* xBestIndex    */ fts3BestIndexMethod,
+  /* xDisconnect   */ fts3DisconnectMethod,
+  /* xDestroy      */ fts3DestroyMethod,
+  /* xOpen         */ fts3OpenMethod,
+  /* xClose        */ fts3CloseMethod,
+  /* xFilter       */ fts3FilterMethod,
+  /* xNext         */ fts3NextMethod,
+  /* xEof          */ fts3EofMethod,
+  /* xColumn       */ fts3ColumnMethod,
+  /* xRowid        */ fts3RowidMethod,
+  /* xUpdate       */ fts3UpdateMethod,
+  /* xBegin        */ fts3BeginMethod,
+  /* xSync         */ fts3SyncMethod,
+  /* xCommit       */ fts3CommitMethod,
+  /* xRollback     */ fts3RollbackMethod,
+  /* xFindFunction */ fts3FindFunctionMethod,
+  /* xRename */       fts3RenameMethod,
 };
 
+/*
+** This function is registered as the module destructor (called when an
+** FTS3 enabled database connection is closed). It frees the memory
+** allocated for the tokenizer hash table.
+*/
 static void hashDestroy(void *p){
-  fts3Hash *pHash = (fts3Hash *)p;
+  Fts3Hash *pHash = (Fts3Hash *)p;
   sqlite3Fts3HashClear(pHash);
   sqlite3_free(pHash);
 }
 
 /*
-** The fts3 built-in tokenizers - "simple" and "porter" - are implemented
-** in files fts3_tokenizer1.c and fts3_porter.c respectively. The following
-** two forward declarations are for functions declared in these files
-** used to retrieve the respective implementations.
+** The fts3 built-in tokenizers - "simple", "porter" and "icu"- are 
+** implemented in files fts3_tokenizer1.c, fts3_porter.c and fts3_icu.c
+** respectively. The following three forward declarations are for functions
+** declared in these files used to retrieve the respective implementations.
 **
 ** Calling sqlite3Fts3SimpleTokenizerModule() sets the value pointed
-** to by the argument to point a the "simple" tokenizer implementation.
-** Function ...PorterTokenizerModule() sets *pModule to point to the
-** porter tokenizer/stemmer implementation.
+** to by the argument to point to the "simple" tokenizer implementation.
+** And so on.
 */
 void sqlite3Fts3SimpleTokenizerModule(sqlite3_tokenizer_module const**ppModule);
 void sqlite3Fts3PorterTokenizerModule(sqlite3_tokenizer_module const**ppModule);
+#ifdef SQLITE_ENABLE_ICU
 void sqlite3Fts3IcuTokenizerModule(sqlite3_tokenizer_module const**ppModule);
-
-int sqlite3Fts3InitHashTable(sqlite3 *, fts3Hash *, const char *);
+#endif
 
 /*
 ** Initialise the fts3 extension. If this extension is built as part
 ** of the sqlite library, then this function is called directly by
 ** SQLite. If fts3 is built as a dynamically loadable extension, this
 ** function is called by the sqlite3_extension_init() entry point.
 */
 int sqlite3Fts3Init(sqlite3 *db){
   int rc = SQLITE_OK;
-  fts3Hash *pHash = 0;
+  Fts3Hash *pHash = 0;
   const sqlite3_tokenizer_module *pSimple = 0;
   const sqlite3_tokenizer_module *pPorter = 0;
+
+#ifdef SQLITE_ENABLE_ICU
   const sqlite3_tokenizer_module *pIcu = 0;
+  sqlite3Fts3IcuTokenizerModule(&pIcu);
+#endif
+
+  rc = sqlite3Fts3InitAux(db);
+  if( rc!=SQLITE_OK ) return rc;
 
   sqlite3Fts3SimpleTokenizerModule(&pSimple);
   sqlite3Fts3PorterTokenizerModule(&pPorter);
-#ifdef SQLITE_ENABLE_ICU
-  sqlite3Fts3IcuTokenizerModule(&pIcu);
-#endif
 
   /* Allocate and initialise the hash-table used to store tokenizers. */
-  pHash = sqlite3_malloc(sizeof(fts3Hash));
+  pHash = sqlite3_malloc(sizeof(Fts3Hash));
   if( !pHash ){
     rc = SQLITE_NOMEM;
   }else{
     sqlite3Fts3HashInit(pHash, FTS3_HASH_STRING, 1);
   }
 
   /* Load the built-in tokenizers into the hash table */
   if( rc==SQLITE_OK ){
     if( sqlite3Fts3HashInsert(pHash, "simple", 7, (void *)pSimple)
      || sqlite3Fts3HashInsert(pHash, "porter", 7, (void *)pPorter) 
+#ifdef SQLITE_ENABLE_ICU
      || (pIcu && sqlite3Fts3HashInsert(pHash, "icu", 4, (void *)pIcu))
+#endif
     ){
       rc = SQLITE_NOMEM;
     }
   }
 
 #ifdef SQLITE_TEST
-  sqlite3Fts3ExprInitTestInterface(db);
+  if( rc==SQLITE_OK ){
+    rc = sqlite3Fts3ExprInitTestInterface(db);
+  }
 #endif
 
   /* Create the virtual table wrapper around the hash-table and overload 
   ** the two scalar functions. If this is successful, register the
   ** module with sqlite.
   */
   if( SQLITE_OK==rc 
 #if CHROMIUM_FTS3_CHANGES && !SQLITE_TEST
       /* fts3_tokenizer() disabled for security reasons. */
 #else
    && SQLITE_OK==(rc = sqlite3Fts3InitHashTable(db, pHash, "fts3_tokenizer"))
 #endif
    && SQLITE_OK==(rc = sqlite3_overload_function(db, "snippet", -1))
-   && SQLITE_OK==(rc = sqlite3_overload_function(db, "offsets", -1))
-   && SQLITE_OK==(rc = sqlite3_overload_function(db, "optimize", -1))
-#ifdef SQLITE_TEST
-   && SQLITE_OK==(rc = sqlite3_overload_function(db, "dump_terms", -1))
-   && SQLITE_OK==(rc = sqlite3_overload_function(db, "dump_doclist", -1))
-#endif
+   && SQLITE_OK==(rc = sqlite3_overload_function(db, "offsets", 1))
+   && SQLITE_OK==(rc = sqlite3_overload_function(db, "matchinfo", 1))
+   && SQLITE_OK==(rc = sqlite3_overload_function(db, "matchinfo", 2))
+   && SQLITE_OK==(rc = sqlite3_overload_function(db, "optimize", 1))
   ){
-    return sqlite3_create_module_v2(
+    rc = sqlite3_create_module_v2(
         db, "fts3", &fts3Module, (void *)pHash, hashDestroy
     );
+#if CHROMIUM_FTS3_CHANGES && !SQLITE_TEST
+    /* Disable fts4 pending review. */
+#else
+    if( rc==SQLITE_OK ){
+      rc = sqlite3_create_module_v2(
+          db, "fts4", &fts3Module, (void *)pHash, 0
+      );
+    }
+#endif
+    return rc;
   }
 
   /* An error has occurred. Delete the hash table and return the error code. */
   assert( rc!=SQLITE_OK );
   if( pHash ){
     sqlite3Fts3HashClear(pHash);
     sqlite3_free(pHash);
   }
   return rc;
 }
 
 #if !SQLITE_CORE
 int sqlite3_extension_init(
   sqlite3 *db, 
   char **pzErrMsg,
   const sqlite3_api_routines *pApi
 ){
   SQLITE_EXTENSION_INIT2(pApi)
   return sqlite3Fts3Init(db);
 }
 #endif
 
-#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3) */
+#endif