[sql] Import reference version of SQLite 3.17..

third_party/sqlite/sqlite-src-3170000/ext/fts3/fts3_write.c

+/*
+** 2009 Oct 23
+**
+** 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 file is part of the SQLite FTS3 extension module. Specifically,
+** this file contains code to insert, update and delete rows from FTS3
+** tables. It also contains code to merge FTS3 b-tree segments. Some
+** of the sub-routines used to merge segments are also used by the query 
+** code in fts3.c.
+*/
+
+#include "fts3Int.h"
+#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS3)
+
+#include <string.h>
+#include <assert.h>
+#include <stdlib.h>
+
+
+#define FTS_MAX_APPENDABLE_HEIGHT 16
+
+/*
+** When full-text index nodes are loaded from disk, the buffer that they
+** are loaded into has the following number of bytes of padding at the end 
+** of it. i.e. if a full-text index node is 900 bytes in size, then a buffer
+** of 920 bytes is allocated for it.
+**
+** This means that if we have a pointer into a buffer containing node data,
+** it is always safe to read up to two varints from it without risking an
+** overread, even if the node data is corrupted.
+*/
+#define FTS3_NODE_PADDING (FTS3_VARINT_MAX*2)
+
+/*
+** Under certain circumstances, b-tree nodes (doclists) can be loaded into
+** memory incrementally instead of all at once. This can be a big performance
+** win (reduced IO and CPU) if SQLite stops calling the virtual table xNext()
+** method before retrieving all query results (as may happen, for example,
+** if a query has a LIMIT clause).
+**
+** Incremental loading is used for b-tree nodes FTS3_NODE_CHUNK_THRESHOLD 
+** bytes and larger. Nodes are loaded in chunks of FTS3_NODE_CHUNKSIZE bytes.
+** The code is written so that the hard lower-limit for each of these values 
+** is 1. Clearly such small values would be inefficient, but can be useful 
+** for testing purposes.
+**
+** If this module is built with SQLITE_TEST defined, these constants may
+** be overridden at runtime for testing purposes. File fts3_test.c contains
+** a Tcl interface to read and write the values.
+*/
+#ifdef SQLITE_TEST
+int test_fts3_node_chunksize = (4*1024);
+int test_fts3_node_chunk_threshold = (4*1024)*4;
+# define FTS3_NODE_CHUNKSIZE       test_fts3_node_chunksize
+# define FTS3_NODE_CHUNK_THRESHOLD test_fts3_node_chunk_threshold
+#else
+# define FTS3_NODE_CHUNKSIZE (4*1024) 
+# define FTS3_NODE_CHUNK_THRESHOLD (FTS3_NODE_CHUNKSIZE*4)
+#endif
+
+/*
+** The two values that may be meaningfully bound to the :1 parameter in
+** statements SQL_REPLACE_STAT and SQL_SELECT_STAT.
+*/
+#define FTS_STAT_DOCTOTAL      0
+#define FTS_STAT_INCRMERGEHINT 1
+#define FTS_STAT_AUTOINCRMERGE 2
+
+/*
+** If FTS_LOG_MERGES is defined, call sqlite3_log() to report each automatic
+** and incremental merge operation that takes place. This is used for 
+** debugging FTS only, it should not usually be turned on in production
+** systems.
+*/
+#ifdef FTS3_LOG_MERGES
+static void fts3LogMerge(int nMerge, sqlite3_int64 iAbsLevel){
+  sqlite3_log(SQLITE_OK, "%d-way merge from level %d", nMerge, (int)iAbsLevel);
+}
+#else
+#define fts3LogMerge(x, y)
+#endif
+
+
+typedef struct PendingList PendingList;
+typedef struct SegmentNode SegmentNode;
+typedef struct SegmentWriter SegmentWriter;
+
+/*
+** An instance of the following data structure is used to build doclists
+** incrementally. See function fts3PendingListAppend() for details.
+*/
+struct PendingList {
+  int nData;
+  char *aData;
+  int nSpace;
+  sqlite3_int64 iLastDocid;
+  sqlite3_int64 iLastCol;
+  sqlite3_int64 iLastPos;
+};
+
+
+/*
+** Each cursor has a (possibly empty) linked list of the following objects.
+*/
+struct Fts3DeferredToken {
+  Fts3PhraseToken *pToken;        /* Pointer to corresponding expr token */
+  int iCol;                       /* Column token must occur in */
+  Fts3DeferredToken *pNext;       /* Next in list of deferred tokens */
+  PendingList *pList;             /* Doclist is assembled here */
+};
+
+/*
+** An instance of this structure is used to iterate through the terms on
+** a contiguous set of segment b-tree leaf nodes. Although the details of
+** this structure are only manipulated by code in this file, opaque handles
+** of type Fts3SegReader* are also used by code in fts3.c to iterate through
+** terms when querying the full-text index. See functions:
+**
+**   sqlite3Fts3SegReaderNew()
+**   sqlite3Fts3SegReaderFree()
+**   sqlite3Fts3SegReaderIterate()
+**
+** Methods used to manipulate Fts3SegReader structures:
+**
+**   fts3SegReaderNext()
+**   fts3SegReaderFirstDocid()
+**   fts3SegReaderNextDocid()
+*/
+struct Fts3SegReader {
+  int iIdx;                       /* Index within level, or 0x7FFFFFFF for PT */
+  u8 bLookup;                     /* True for a lookup only */
+  u8 rootOnly;                    /* True for a root-only reader */
+
+  sqlite3_int64 iStartBlock;      /* Rowid of first leaf block to traverse */
+  sqlite3_int64 iLeafEndBlock;    /* Rowid of final leaf block to traverse */
+  sqlite3_int64 iEndBlock;        /* Rowid of final block in segment (or 0) */
+  sqlite3_int64 iCurrentBlock;    /* Current leaf block (or 0) */
+
+  char *aNode;                    /* Pointer to node data (or NULL) */
+  int nNode;                      /* Size of buffer at aNode (or 0) */
+  int nPopulate;                  /* If >0, bytes of buffer aNode[] loaded */
+  sqlite3_blob *pBlob;            /* If not NULL, blob handle to read node */
+
+  Fts3HashElem **ppNextElem;
+
+  /* Variables set by fts3SegReaderNext(). These may be read directly
+  ** by the caller. They are valid from the time SegmentReaderNew() returns
+  ** until SegmentReaderNext() returns something other than SQLITE_OK
+  ** (i.e. SQLITE_DONE).
+  */
+  int nTerm;                      /* Number of bytes in current term */
+  char *zTerm;                    /* Pointer to current term */
+  int nTermAlloc;                 /* Allocated size of zTerm buffer */
+  char *aDoclist;                 /* Pointer to doclist of current entry */
+  int nDoclist;                   /* Size of doclist in current entry */
+
+  /* The following variables are used by fts3SegReaderNextDocid() to iterate 
+  ** through the current doclist (aDoclist/nDoclist).
+  */
+  char *pOffsetList;
+  int nOffsetList;                /* For descending pending seg-readers only */
+  sqlite3_int64 iDocid;
+};
+
+#define fts3SegReaderIsPending(p) ((p)->ppNextElem!=0)
+#define fts3SegReaderIsRootOnly(p) ((p)->rootOnly!=0)
+
+/*
+** An instance of this structure is used to create a segment b-tree in the
+** database. The internal details of this type are only accessed by the
+** following functions:
+**
+**   fts3SegWriterAdd()
+**   fts3SegWriterFlush()
+**   fts3SegWriterFree()
+*/
+struct SegmentWriter {
+  SegmentNode *pTree;             /* Pointer to interior tree structure */
+  sqlite3_int64 iFirst;           /* First slot in %_segments written */
+  sqlite3_int64 iFree;            /* Next free slot in %_segments */
+  char *zTerm;                    /* Pointer to previous term buffer */
+  int nTerm;                      /* Number of bytes in zTerm */
+  int nMalloc;                    /* Size of malloc'd buffer at zMalloc */
+  char *zMalloc;                  /* Malloc'd space (possibly) used for zTerm */
+  int nSize;                      /* Size of allocation at aData */
+  int nData;                      /* Bytes of data in aData */
+  char *aData;                    /* Pointer to block from malloc() */
+  i64 nLeafData;                  /* Number of bytes of leaf data written */
+};
+
+/*
+** Type SegmentNode is used by the following three functions to create
+** the interior part of the segment b+-tree structures (everything except
+** the leaf nodes). These functions and type are only ever used by code
+** within the fts3SegWriterXXX() family of functions described above.
+**
+**   fts3NodeAddTerm()
+**   fts3NodeWrite()
+**   fts3NodeFree()
+**
+** When a b+tree is written to the database (either as a result of a merge
+** or the pending-terms table being flushed), leaves are written into the 
+** database file as soon as they are completely populated. The interior of
+** the tree is assembled in memory and written out only once all leaves have
+** been populated and stored. This is Ok, as the b+-tree fanout is usually
+** very large, meaning that the interior of the tree consumes relatively 
+** little memory.
+*/
+struct SegmentNode {
+  SegmentNode *pParent;           /* Parent node (or NULL for root node) */
+  SegmentNode *pRight;            /* Pointer to right-sibling */
+  SegmentNode *pLeftmost;         /* Pointer to left-most node of this depth */
+  int nEntry;                     /* Number of terms written to node so far */
+  char *zTerm;                    /* Pointer to previous term buffer */
+  int nTerm;                      /* Number of bytes in zTerm */
+  int nMalloc;                    /* Size of malloc'd buffer at zMalloc */
+  char *zMalloc;                  /* Malloc'd space (possibly) used for zTerm */
+  int nData;                      /* Bytes of valid data so far */
+  char *aData;                    /* Node data */
+};
+
+/*
+** Valid values for the second argument to fts3SqlStmt().
+*/
+#define SQL_DELETE_CONTENT             0
+#define SQL_IS_EMPTY                   1
+#define SQL_DELETE_ALL_CONTENT         2 
+#define SQL_DELETE_ALL_SEGMENTS        3
+#define SQL_DELETE_ALL_SEGDIR          4
+#define SQL_DELETE_ALL_DOCSIZE         5
+#define SQL_DELETE_ALL_STAT            6
+#define SQL_SELECT_CONTENT_BY_ROWID    7
+#define SQL_NEXT_SEGMENT_INDEX         8
+#define SQL_INSERT_SEGMENTS            9
+#define SQL_NEXT_SEGMENTS_ID          10
+#define SQL_INSERT_SEGDIR             11
+#define SQL_SELECT_LEVEL              12
+#define SQL_SELECT_LEVEL_RANGE        13
+#define SQL_SELECT_LEVEL_COUNT        14
+#define SQL_SELECT_SEGDIR_MAX_LEVEL   15
+#define SQL_DELETE_SEGDIR_LEVEL       16
+#define SQL_DELETE_SEGMENTS_RANGE     17
+#define SQL_CONTENT_INSERT            18
+#define SQL_DELETE_DOCSIZE            19
+#define SQL_REPLACE_DOCSIZE           20
+#define SQL_SELECT_DOCSIZE            21
+#define SQL_SELECT_STAT               22
+#define SQL_REPLACE_STAT              23
+
+#define SQL_SELECT_ALL_PREFIX_LEVEL   24
+#define SQL_DELETE_ALL_TERMS_SEGDIR   25
+#define SQL_DELETE_SEGDIR_RANGE       26
+#define SQL_SELECT_ALL_LANGID         27
+#define SQL_FIND_MERGE_LEVEL          28
+#define SQL_MAX_LEAF_NODE_ESTIMATE    29
+#define SQL_DELETE_SEGDIR_ENTRY       30
+#define SQL_SHIFT_SEGDIR_ENTRY        31
+#define SQL_SELECT_SEGDIR             32
+#define SQL_CHOMP_SEGDIR              33
+#define SQL_SEGMENT_IS_APPENDABLE     34
+#define SQL_SELECT_INDEXES            35
+#define SQL_SELECT_MXLEVEL            36
+
+#define SQL_SELECT_LEVEL_RANGE2       37
+#define SQL_UPDATE_LEVEL_IDX          38
+#define SQL_UPDATE_LEVEL              39
+
+/*
+** This function is used to obtain an SQLite prepared statement handle
+** for the statement identified by the second argument. If successful,
+** *pp is set to the requested statement handle and SQLITE_OK returned.
+** Otherwise, an SQLite error code is returned and *pp is set to 0.
+**
+** If argument apVal is not NULL, then it must point to an array with
+** at least as many entries as the requested statement has bound 
+** parameters. The values are bound to the statements parameters before
+** returning.
+*/
+static int fts3SqlStmt(
+  Fts3Table *p,                   /* Virtual table handle */
+  int eStmt,                      /* One of the SQL_XXX constants above */
+  sqlite3_stmt **pp,              /* OUT: Statement handle */
+  sqlite3_value **apVal           /* Values to bind to statement */
+){
+  const char *azSql[] = {
+/* 0  */  "DELETE FROM %Q.'%q_content' WHERE rowid = ?",
+/* 1  */  "SELECT NOT EXISTS(SELECT docid FROM %Q.'%q_content' WHERE rowid!=?)",
+/* 2  */  "DELETE FROM %Q.'%q_content'",
+/* 3  */  "DELETE FROM %Q.'%q_segments'",
+/* 4  */  "DELETE FROM %Q.'%q_segdir'",
+/* 5  */  "DELETE FROM %Q.'%q_docsize'",
+/* 6  */  "DELETE FROM %Q.'%q_stat'",
+/* 7  */  "SELECT %s WHERE rowid=?",
+/* 8  */  "SELECT (SELECT max(idx) FROM %Q.'%q_segdir' WHERE level = ?) + 1",
+/* 9  */  "REPLACE INTO %Q.'%q_segments'(blockid, block) VALUES(?, ?)",
+/* 10 */  "SELECT coalesce((SELECT max(blockid) FROM %Q.'%q_segments') + 1, 1)",
+/* 11 */  "REPLACE INTO %Q.'%q_segdir' VALUES(?,?,?,?,?,?)",
+
+          /* Return segments in order from oldest to newest.*/ 
+/* 12 */  "SELECT idx, start_block, leaves_end_block, end_block, root "
+            "FROM %Q.'%q_segdir' WHERE level = ? ORDER BY idx ASC",
+/* 13 */  "SELECT idx, start_block, leaves_end_block, end_block, root "
+            "FROM %Q.'%q_segdir' WHERE level BETWEEN ? AND ?"
+            "ORDER BY level DESC, idx ASC",
+
+/* 14 */  "SELECT count(*) FROM %Q.'%q_segdir' WHERE level = ?",
+/* 15 */  "SELECT max(level) FROM %Q.'%q_segdir' WHERE level BETWEEN ? AND ?",
+
+/* 16 */  "DELETE FROM %Q.'%q_segdir' WHERE level = ?",
+/* 17 */  "DELETE FROM %Q.'%q_segments' WHERE blockid BETWEEN ? AND ?",
+/* 18 */  "INSERT INTO %Q.'%q_content' VALUES(%s)",
+/* 19 */  "DELETE FROM %Q.'%q_docsize' WHERE docid = ?",
+/* 20 */  "REPLACE INTO %Q.'%q_docsize' VALUES(?,?)",
+/* 21 */  "SELECT size FROM %Q.'%q_docsize' WHERE docid=?",
+/* 22 */  "SELECT value FROM %Q.'%q_stat' WHERE id=?",
+/* 23 */  "REPLACE INTO %Q.'%q_stat' VALUES(?,?)",
+/* 24 */  "",
+/* 25 */  "",
+
+/* 26 */ "DELETE FROM %Q.'%q_segdir' WHERE level BETWEEN ? AND ?",
+/* 27 */ "SELECT ? UNION SELECT level / (1024 * ?) FROM %Q.'%q_segdir'",
+
+/* This statement is used to determine which level to read the input from
+** when performing an incremental merge. It returns the absolute level number
+** of the oldest level in the db that contains at least ? segments. Or,
+** if no level in the FTS index contains more than ? segments, the statement
+** returns zero rows.  */
+/* 28 */ "SELECT level, count(*) AS cnt FROM %Q.'%q_segdir' "
+         "  GROUP BY level HAVING cnt>=?"
+         "  ORDER BY (level %% 1024) ASC LIMIT 1",
+
+/* Estimate the upper limit on the number of leaf nodes in a new segment
+** created by merging the oldest :2 segments from absolute level :1. See 
+** function sqlite3Fts3Incrmerge() for details.  */
+/* 29 */ "SELECT 2 * total(1 + leaves_end_block - start_block) "
+         "  FROM %Q.'%q_segdir' WHERE level = ? AND idx < ?",
+
+/* SQL_DELETE_SEGDIR_ENTRY
+**   Delete the %_segdir entry on absolute level :1 with index :2.  */
+/* 30 */ "DELETE FROM %Q.'%q_segdir' WHERE level = ? AND idx = ?",
+
+/* SQL_SHIFT_SEGDIR_ENTRY
+**   Modify the idx value for the segment with idx=:3 on absolute level :2
+**   to :1.  */
+/* 31 */ "UPDATE %Q.'%q_segdir' SET idx = ? WHERE level=? AND idx=?",
+
+/* SQL_SELECT_SEGDIR
+**   Read a single entry from the %_segdir table. The entry from absolute 
+**   level :1 with index value :2.  */
+/* 32 */  "SELECT idx, start_block, leaves_end_block, end_block, root "
+            "FROM %Q.'%q_segdir' WHERE level = ? AND idx = ?",
+
+/* SQL_CHOMP_SEGDIR
+**   Update the start_block (:1) and root (:2) fields of the %_segdir
+**   entry located on absolute level :3 with index :4.  */
+/* 33 */  "UPDATE %Q.'%q_segdir' SET start_block = ?, root = ?"
+            "WHERE level = ? AND idx = ?",
+
+/* SQL_SEGMENT_IS_APPENDABLE
+**   Return a single row if the segment with end_block=? is appendable. Or
+**   no rows otherwise.  */
+/* 34 */  "SELECT 1 FROM %Q.'%q_segments' WHERE blockid=? AND block IS NULL",
+
+/* SQL_SELECT_INDEXES
+**   Return the list of valid segment indexes for absolute level ?  */
+/* 35 */  "SELECT idx FROM %Q.'%q_segdir' WHERE level=? ORDER BY 1 ASC",
+
+/* SQL_SELECT_MXLEVEL
+**   Return the largest relative level in the FTS index or indexes.  */
+/* 36 */  "SELECT max( level %% 1024 ) FROM %Q.'%q_segdir'",
+
+          /* Return segments in order from oldest to newest.*/ 
+/* 37 */  "SELECT level, idx, end_block "
+            "FROM %Q.'%q_segdir' WHERE level BETWEEN ? AND ? "
+            "ORDER BY level DESC, idx ASC",
+
+          /* Update statements used while promoting segments */
+/* 38 */  "UPDATE OR FAIL %Q.'%q_segdir' SET level=-1,idx=? "
+            "WHERE level=? AND idx=?",
+/* 39 */  "UPDATE OR FAIL %Q.'%q_segdir' SET level=? WHERE level=-1"
+
+  };
+  int rc = SQLITE_OK;
+  sqlite3_stmt *pStmt;
+
+  assert( SizeofArray(azSql)==SizeofArray(p->aStmt) );
+  assert( eStmt<SizeofArray(azSql) && eStmt>=0 );
+  
+  pStmt = p->aStmt[eStmt];
+  if( !pStmt ){
+    char *zSql;
+    if( eStmt==SQL_CONTENT_INSERT ){
+      zSql = sqlite3_mprintf(azSql[eStmt], p->zDb, p->zName, p->zWriteExprlist);
+    }else if( eStmt==SQL_SELECT_CONTENT_BY_ROWID ){
+      zSql = sqlite3_mprintf(azSql[eStmt], p->zReadExprlist);
+    }else{
+      zSql = sqlite3_mprintf(azSql[eStmt], p->zDb, p->zName);
+    }
+    if( !zSql ){
+      rc = SQLITE_NOMEM;
+    }else{
+      rc = sqlite3_prepare_v2(p->db, zSql, -1, &pStmt, NULL);
+      sqlite3_free(zSql);
+      assert( rc==SQLITE_OK || pStmt==0 );
+      p->aStmt[eStmt] = pStmt;
+    }
+  }
+  if( apVal ){
+    int i;
+    int nParam = sqlite3_bind_parameter_count(pStmt);
+    for(i=0; rc==SQLITE_OK && i<nParam; i++){
+      rc = sqlite3_bind_value(pStmt, i+1, apVal[i]);
+    }
+  }
+  *pp = pStmt;
+  return rc;
+}
+
+
+static int fts3SelectDocsize(
+  Fts3Table *pTab,                /* FTS3 table handle */
+  sqlite3_int64 iDocid,           /* Docid to bind for SQL_SELECT_DOCSIZE */
+  sqlite3_stmt **ppStmt           /* OUT: Statement handle */
+){
+  sqlite3_stmt *pStmt = 0;        /* Statement requested from fts3SqlStmt() */
+  int rc;                         /* Return code */
+
+  rc = fts3SqlStmt(pTab, SQL_SELECT_DOCSIZE, &pStmt, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pStmt, 1, iDocid);
+    rc = sqlite3_step(pStmt);
+    if( rc!=SQLITE_ROW || sqlite3_column_type(pStmt, 0)!=SQLITE_BLOB ){
+      rc = sqlite3_reset(pStmt);
+      if( rc==SQLITE_OK ) rc = FTS_CORRUPT_VTAB;
+      pStmt = 0;
+    }else{
+      rc = SQLITE_OK;
+    }
+  }
+
+  *ppStmt = pStmt;
+  return rc;
+}
+
+int sqlite3Fts3SelectDoctotal(
+  Fts3Table *pTab,                /* Fts3 table handle */
+  sqlite3_stmt **ppStmt           /* OUT: Statement handle */
+){
+  sqlite3_stmt *pStmt = 0;
+  int rc;
+  rc = fts3SqlStmt(pTab, SQL_SELECT_STAT, &pStmt, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int(pStmt, 1, FTS_STAT_DOCTOTAL);
+    if( sqlite3_step(pStmt)!=SQLITE_ROW
+     || sqlite3_column_type(pStmt, 0)!=SQLITE_BLOB
+    ){
+      rc = sqlite3_reset(pStmt);
+      if( rc==SQLITE_OK ) rc = FTS_CORRUPT_VTAB;
+      pStmt = 0;
+    }
+  }
+  *ppStmt = pStmt;
+  return rc;
+}
+
+int sqlite3Fts3SelectDocsize(
+  Fts3Table *pTab,                /* Fts3 table handle */
+  sqlite3_int64 iDocid,           /* Docid to read size data for */
+  sqlite3_stmt **ppStmt           /* OUT: Statement handle */
+){
+  return fts3SelectDocsize(pTab, iDocid, ppStmt);
+}
+
+/*
+** Similar to fts3SqlStmt(). Except, after binding the parameters in
+** array apVal[] to the SQL statement identified by eStmt, the statement
+** is executed.
+**
+** Returns SQLITE_OK if the statement is successfully executed, or an
+** SQLite error code otherwise.
+*/
+static void fts3SqlExec(
+  int *pRC,                /* Result code */
+  Fts3Table *p,            /* The FTS3 table */
+  int eStmt,               /* Index of statement to evaluate */
+  sqlite3_value **apVal    /* Parameters to bind */
+){
+  sqlite3_stmt *pStmt;
+  int rc;
+  if( *pRC ) return;
+  rc = fts3SqlStmt(p, eStmt, &pStmt, apVal); 
+  if( rc==SQLITE_OK ){
+    sqlite3_step(pStmt);
+    rc = sqlite3_reset(pStmt);
+  }
+  *pRC = rc;
+}
+
+
+/*
+** This function ensures that the caller has obtained an exclusive 
+** shared-cache table-lock on the %_segdir table. This is required before 
+** writing data to the fts3 table. If this lock is not acquired first, then
+** the caller may end up attempting to take this lock as part of committing
+** a transaction, causing SQLite to return SQLITE_LOCKED or 
+** LOCKED_SHAREDCACHEto a COMMIT command.
+**
+** It is best to avoid this because if FTS3 returns any error when 
+** committing a transaction, the whole transaction will be rolled back. 
+** And this is not what users expect when they get SQLITE_LOCKED_SHAREDCACHE. 
+** It can still happen if the user locks the underlying tables directly 
+** instead of accessing them via FTS.
+*/
+static int fts3Writelock(Fts3Table *p){
+  int rc = SQLITE_OK;
+  
+  if( p->nPendingData==0 ){
+    sqlite3_stmt *pStmt;
+    rc = fts3SqlStmt(p, SQL_DELETE_SEGDIR_LEVEL, &pStmt, 0);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_null(pStmt, 1);
+      sqlite3_step(pStmt);
+      rc = sqlite3_reset(pStmt);
+    }
+  }
+
+  return rc;
+}
+
+/*
+** FTS maintains a separate indexes for each language-id (a 32-bit integer).
+** Within each language id, a separate index is maintained to store the
+** document terms, and each configured prefix size (configured the FTS 
+** "prefix=" option). And each index consists of multiple levels ("relative
+** levels").
+**
+** All three of these values (the language id, the specific index and the
+** level within the index) are encoded in 64-bit integer values stored
+** in the %_segdir table on disk. This function is used to convert three
+** separate component values into the single 64-bit integer value that
+** can be used to query the %_segdir table.
+**
+** Specifically, each language-id/index combination is allocated 1024 
+** 64-bit integer level values ("absolute levels"). The main terms index
+** for language-id 0 is allocate values 0-1023. The first prefix index
+** (if any) for language-id 0 is allocated values 1024-2047. And so on.
+** Language 1 indexes are allocated immediately following language 0.
+**
+** So, for a system with nPrefix prefix indexes configured, the block of
+** absolute levels that corresponds to language-id iLangid and index 
+** iIndex starts at absolute level ((iLangid * (nPrefix+1) + iIndex) * 1024).
+*/
+static sqlite3_int64 getAbsoluteLevel(
+  Fts3Table *p,                   /* FTS3 table handle */
+  int iLangid,                    /* Language id */
+  int iIndex,                     /* Index in p->aIndex[] */
+  int iLevel                      /* Level of segments */
+){
+  sqlite3_int64 iBase;            /* First absolute level for iLangid/iIndex */
+  assert( iLangid>=0 );
+  assert( p->nIndex>0 );
+  assert( iIndex>=0 && iIndex<p->nIndex );
+
+  iBase = ((sqlite3_int64)iLangid * p->nIndex + iIndex) * FTS3_SEGDIR_MAXLEVEL;
+  return iBase + iLevel;
+}
+
+/*
+** Set *ppStmt to a statement handle that may be used to iterate through
+** all rows in the %_segdir table, from oldest to newest. If successful,
+** return SQLITE_OK. If an error occurs while preparing the statement, 
+** return an SQLite error code.
+**
+** There is only ever one instance of this SQL statement compiled for
+** each FTS3 table.
+**
+** The statement returns the following columns from the %_segdir table:
+**
+**   0: idx
+**   1: start_block
+**   2: leaves_end_block
+**   3: end_block
+**   4: root
+*/
+int sqlite3Fts3AllSegdirs(
+  Fts3Table *p,                   /* FTS3 table */
+  int iLangid,                    /* Language being queried */
+  int iIndex,                     /* Index for p->aIndex[] */
+  int iLevel,                     /* Level to select (relative level) */
+  sqlite3_stmt **ppStmt           /* OUT: Compiled statement */
+){
+  int rc;
+  sqlite3_stmt *pStmt = 0;
+
+  assert( iLevel==FTS3_SEGCURSOR_ALL || iLevel>=0 );
+  assert( iLevel<FTS3_SEGDIR_MAXLEVEL );
+  assert( iIndex>=0 && iIndex<p->nIndex );
+
+  if( iLevel<0 ){
+    /* "SELECT * FROM %_segdir WHERE level BETWEEN ? AND ? ORDER BY ..." */
+    rc = fts3SqlStmt(p, SQL_SELECT_LEVEL_RANGE, &pStmt, 0);
+    if( rc==SQLITE_OK ){ 
+      sqlite3_bind_int64(pStmt, 1, getAbsoluteLevel(p, iLangid, iIndex, 0));
+      sqlite3_bind_int64(pStmt, 2, 
+          getAbsoluteLevel(p, iLangid, iIndex, FTS3_SEGDIR_MAXLEVEL-1)
+      );
+    }
+  }else{
+    /* "SELECT * FROM %_segdir WHERE level = ? ORDER BY ..." */
+    rc = fts3SqlStmt(p, SQL_SELECT_LEVEL, &pStmt, 0);
+    if( rc==SQLITE_OK ){ 
+      sqlite3_bind_int64(pStmt, 1, getAbsoluteLevel(p, iLangid, iIndex,iLevel));
+    }
+  }
+  *ppStmt = pStmt;
+  return rc;
+}
+
+
+/*
+** Append a single varint to a PendingList buffer. SQLITE_OK is returned
+** if successful, or an SQLite error code otherwise.
+**
+** This function also serves to allocate the PendingList structure itself.
+** For example, to create a new PendingList structure containing two
+** varints:
+**
+**   PendingList *p = 0;
+**   fts3PendingListAppendVarint(&p, 1);
+**   fts3PendingListAppendVarint(&p, 2);
+*/
+static int fts3PendingListAppendVarint(
+  PendingList **pp,               /* IN/OUT: Pointer to PendingList struct */
+  sqlite3_int64 i                 /* Value to append to data */
+){
+  PendingList *p = *pp;
+
+  /* Allocate or grow the PendingList as required. */
+  if( !p ){
+    p = sqlite3_malloc(sizeof(*p) + 100);
+    if( !p ){
+      return SQLITE_NOMEM;
+    }
+    p->nSpace = 100;
+    p->aData = (char *)&p[1];
+    p->nData = 0;
+  }
+  else if( p->nData+FTS3_VARINT_MAX+1>p->nSpace ){
+    int nNew = p->nSpace * 2;
+    p = sqlite3_realloc(p, sizeof(*p) + nNew);
+    if( !p ){
+      sqlite3_free(*pp);
+      *pp = 0;
+      return SQLITE_NOMEM;
+    }
+    p->nSpace = nNew;
+    p->aData = (char *)&p[1];
+  }
+
+  /* Append the new serialized varint to the end of the list. */
+  p->nData += sqlite3Fts3PutVarint(&p->aData[p->nData], i);
+  p->aData[p->nData] = '\0';
+  *pp = p;
+  return SQLITE_OK;
+}
+
+/*
+** Add a docid/column/position entry to a PendingList structure. Non-zero
+** is returned if the structure is sqlite3_realloced as part of adding
+** the entry. Otherwise, zero.
+**
+** If an OOM error occurs, *pRc is set to SQLITE_NOMEM before returning.
+** Zero is always returned in this case. Otherwise, if no OOM error occurs,
+** it is set to SQLITE_OK.
+*/
+static int fts3PendingListAppend(
+  PendingList **pp,               /* IN/OUT: PendingList structure */
+  sqlite3_int64 iDocid,           /* Docid for entry to add */
+  sqlite3_int64 iCol,             /* Column for entry to add */
+  sqlite3_int64 iPos,             /* Position of term for entry to add */
+  int *pRc                        /* OUT: Return code */
+){
+  PendingList *p = *pp;
+  int rc = SQLITE_OK;
+
+  assert( !p || p->iLastDocid<=iDocid );
+
+  if( !p || p->iLastDocid!=iDocid ){
+    sqlite3_int64 iDelta = iDocid - (p ? p->iLastDocid : 0);
+    if( p ){
+      assert( p->nData<p->nSpace );
+      assert( p->aData[p->nData]==0 );
+      p->nData++;
+    }
+    if( SQLITE_OK!=(rc = fts3PendingListAppendVarint(&p, iDelta)) ){
+      goto pendinglistappend_out;
+    }
+    p->iLastCol = -1;
+    p->iLastPos = 0;
+    p->iLastDocid = iDocid;
+  }
+  if( iCol>0 && p->iLastCol!=iCol ){
+    if( SQLITE_OK!=(rc = fts3PendingListAppendVarint(&p, 1))
+     || SQLITE_OK!=(rc = fts3PendingListAppendVarint(&p, iCol))
+    ){
+      goto pendinglistappend_out;
+    }
+    p->iLastCol = iCol;
+    p->iLastPos = 0;
+  }
+  if( iCol>=0 ){
+    assert( iPos>p->iLastPos || (iPos==0 && p->iLastPos==0) );
+    rc = fts3PendingListAppendVarint(&p, 2+iPos-p->iLastPos);
+    if( rc==SQLITE_OK ){
+      p->iLastPos = iPos;
+    }
+  }
+
+ pendinglistappend_out:
+  *pRc = rc;
+  if( p!=*pp ){
+    *pp = p;
+    return 1;
+  }
+  return 0;
+}
+
+/*
+** Free a PendingList object allocated by fts3PendingListAppend().
+*/
+static void fts3PendingListDelete(PendingList *pList){
+  sqlite3_free(pList);
+}
+
+/*
+** Add an entry to one of the pending-terms hash tables.
+*/
+static int fts3PendingTermsAddOne(
+  Fts3Table *p,
+  int iCol,
+  int iPos,
+  Fts3Hash *pHash,                /* Pending terms hash table to add entry to */
+  const char *zToken,
+  int nToken
+){
+  PendingList *pList;
+  int rc = SQLITE_OK;
+
+  pList = (PendingList *)fts3HashFind(pHash, zToken, nToken);
+  if( pList ){
+    p->nPendingData -= (pList->nData + nToken + sizeof(Fts3HashElem));
+  }
+  if( fts3PendingListAppend(&pList, p->iPrevDocid, iCol, iPos, &rc) ){
+    if( pList==fts3HashInsert(pHash, zToken, nToken, pList) ){
+      /* Malloc failed while inserting the new entry. This can only 
+      ** happen if there was no previous entry for this token.
+      */
+      assert( 0==fts3HashFind(pHash, zToken, nToken) );
+      sqlite3_free(pList);
+      rc = SQLITE_NOMEM;
+    }
+  }
+  if( rc==SQLITE_OK ){
+    p->nPendingData += (pList->nData + nToken + sizeof(Fts3HashElem));
+  }
+  return rc;
+}
+
+/*
+** Tokenize the nul-terminated string zText and add all tokens to the
+** pending-terms hash-table. The docid used is that currently stored in
+** p->iPrevDocid, and the column is specified by argument iCol.
+**
+** If successful, SQLITE_OK is returned. Otherwise, an SQLite error code.
+*/
+static int fts3PendingTermsAdd(
+  Fts3Table *p,                   /* Table into which text will be inserted */
+  int iLangid,                    /* Language id to use */
+  const char *zText,              /* Text of document to be inserted */
+  int iCol,                       /* Column into which text is being inserted */
+  u32 *pnWord                     /* IN/OUT: Incr. by number tokens inserted */
+){
+  int rc;
+  int iStart = 0;
+  int iEnd = 0;
+  int iPos = 0;
+  int nWord = 0;
+
+  char const *zToken;
+  int nToken = 0;
+
+  sqlite3_tokenizer *pTokenizer = p->pTokenizer;
+  sqlite3_tokenizer_module const *pModule = pTokenizer->pModule;
+  sqlite3_tokenizer_cursor *pCsr;
+  int (*xNext)(sqlite3_tokenizer_cursor *pCursor,
+      const char**,int*,int*,int*,int*);
+
+  assert( pTokenizer && pModule );
+
+  /* If the user has inserted a NULL value, this function may be called with
+  ** zText==0. In this case, add zero token entries to the hash table and 
+  ** return early. */
+  if( zText==0 ){
+    *pnWord = 0;
+    return SQLITE_OK;
+  }
+
+  rc = sqlite3Fts3OpenTokenizer(pTokenizer, iLangid, zText, -1, &pCsr);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  xNext = pModule->xNext;
+  while( SQLITE_OK==rc
+      && SQLITE_OK==(rc = xNext(pCsr, &zToken, &nToken, &iStart, &iEnd, &iPos))
+  ){
+    int i;
+    if( iPos>=nWord ) nWord = iPos+1;
+
+    /* Positions cannot be negative; we use -1 as a terminator internally.
+    ** Tokens must have a non-zero length.
+    */
+    if( iPos<0 || !zToken || nToken<=0 ){
+      rc = SQLITE_ERROR;
+      break;
+    }
+
+    /* Add the term to the terms index */
+    rc = fts3PendingTermsAddOne(
+        p, iCol, iPos, &p->aIndex[0].hPending, zToken, nToken
+    );
+    
+    /* Add the term to each of the prefix indexes that it is not too 
+    ** short for. */
+    for(i=1; rc==SQLITE_OK && i<p->nIndex; i++){
+      struct Fts3Index *pIndex = &p->aIndex[i];
+      if( nToken<pIndex->nPrefix ) continue;
+      rc = fts3PendingTermsAddOne(
+          p, iCol, iPos, &pIndex->hPending, zToken, pIndex->nPrefix
+      );
+    }
+  }
+
+  pModule->xClose(pCsr);
+  *pnWord += nWord;
+  return (rc==SQLITE_DONE ? SQLITE_OK : rc);
+}
+
+/* 
+** Calling this function indicates that subsequent calls to 
+** fts3PendingTermsAdd() are to add term/position-list pairs for the
+** contents of the document with docid iDocid.
+*/
+static int fts3PendingTermsDocid(
+  Fts3Table *p,                   /* Full-text table handle */
+  int bDelete,                    /* True if this op is a delete */
+  int iLangid,                    /* Language id of row being written */
+  sqlite_int64 iDocid             /* Docid of row being written */
+){
+  assert( iLangid>=0 );
+  assert( bDelete==1 || bDelete==0 );
+
+  /* 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<p->iPrevDocid 
+   || (iDocid==p->iPrevDocid && p->bPrevDelete==0)
+   || p->iPrevLangid!=iLangid
+   || p->nPendingData>p->nMaxPendingData 
+  ){
+    int rc = sqlite3Fts3PendingTermsFlush(p);
+    if( rc!=SQLITE_OK ) return rc;
+  }
+  p->iPrevDocid = iDocid;
+  p->iPrevLangid = iLangid;
+  p->bPrevDelete = bDelete;
+  return SQLITE_OK;
+}
+
+/*
+** Discard the contents of the pending-terms hash tables. 
+*/
+void sqlite3Fts3PendingTermsClear(Fts3Table *p){
+  int i;
+  for(i=0; i<p->nIndex; i++){
+    Fts3HashElem *pElem;
+    Fts3Hash *pHash = &p->aIndex[i].hPending;
+    for(pElem=fts3HashFirst(pHash); pElem; pElem=fts3HashNext(pElem)){
+      PendingList *pList = (PendingList *)fts3HashData(pElem);
+      fts3PendingListDelete(pList);
+    }
+    fts3HashClear(pHash);
+  }
+  p->nPendingData = 0;
+}
+
+/*
+** This function is called by the xUpdate() method as part of an INSERT
+** operation. It adds entries for each term in the new record to the
+** pendingTerms hash table.
+**
+** Argument apVal is the same as the similarly named argument passed to
+** fts3InsertData(). Parameter iDocid is the docid of the new row.
+*/
+static int fts3InsertTerms(
+  Fts3Table *p, 
+  int iLangid, 
+  sqlite3_value **apVal, 
+  u32 *aSz
+){
+  int i;                          /* Iterator variable */
+  for(i=2; i<p->nColumn+2; i++){
+    int iCol = i-2;
+    if( p->abNotindexed[iCol]==0 ){
+      const char *zText = (const char *)sqlite3_value_text(apVal[i]);
+      int rc = fts3PendingTermsAdd(p, iLangid, zText, iCol, &aSz[iCol]);
+      if( rc!=SQLITE_OK ){
+        return rc;
+      }
+      aSz[p->nColumn] += sqlite3_value_bytes(apVal[i]);
+    }
+  }
+  return SQLITE_OK;
+}
+
+/*
+** This function is called by the xUpdate() method for an INSERT operation.
+** The apVal parameter is passed a copy of the apVal argument passed by
+** SQLite to the xUpdate() method. i.e:
+**
+**   apVal[0]                Not used for INSERT.
+**   apVal[1]                rowid
+**   apVal[2]                Left-most user-defined column
+**   ...
+**   apVal[p->nColumn+1]     Right-most user-defined column
+**   apVal[p->nColumn+2]     Hidden column with same name as table
+**   apVal[p->nColumn+3]     Hidden "docid" column (alias for rowid)
+**   apVal[p->nColumn+4]     Hidden languageid column
+*/
+static int fts3InsertData(
+  Fts3Table *p,                   /* Full-text table */
+  sqlite3_value **apVal,          /* Array of values to insert */
+  sqlite3_int64 *piDocid          /* OUT: Docid for row just inserted */
+){
+  int rc;                         /* Return code */
+  sqlite3_stmt *pContentInsert;   /* INSERT INTO %_content VALUES(...) */
+
+  if( p->zContentTbl ){
+    sqlite3_value *pRowid = apVal[p->nColumn+3];
+    if( sqlite3_value_type(pRowid)==SQLITE_NULL ){
+      pRowid = apVal[1];
+    }
+    if( sqlite3_value_type(pRowid)!=SQLITE_INTEGER ){
+      return SQLITE_CONSTRAINT;
+    }
+    *piDocid = sqlite3_value_int64(pRowid);
+    return SQLITE_OK;
+  }
+
+  /* Locate the statement handle used to insert data into the %_content
+  ** table. The SQL for this statement is:
+  **
+  **   INSERT INTO %_content VALUES(?, ?, ?, ...)
+  **
+  ** The statement features N '?' variables, where N is the number of user
+  ** defined columns in the FTS3 table, plus one for the docid field.
+  */
+  rc = fts3SqlStmt(p, SQL_CONTENT_INSERT, &pContentInsert, &apVal[1]);
+  if( rc==SQLITE_OK && p->zLanguageid ){
+    rc = sqlite3_bind_int(
+        pContentInsert, p->nColumn+2, 
+        sqlite3_value_int(apVal[p->nColumn+4])
+    );
+  }
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* There is a quirk here. The users INSERT statement may have specified
+  ** a value for the "rowid" field, for the "docid" field, or for both.
+  ** Which is a problem, since "rowid" and "docid" are aliases for the
+  ** same value. For example:
+  **
+  **   INSERT INTO fts3tbl(rowid, docid) VALUES(1, 2);
+  **
+  ** In FTS3, this is an error. It is an error to specify non-NULL values
+  ** for both docid and some other rowid alias.
+  */
+  if( SQLITE_NULL!=sqlite3_value_type(apVal[3+p->nColumn]) ){
+    if( SQLITE_NULL==sqlite3_value_type(apVal[0])
+     && SQLITE_NULL!=sqlite3_value_type(apVal[1])
+    ){
+      /* A rowid/docid conflict. */
+      return SQLITE_ERROR;
+    }
+    rc = sqlite3_bind_value(pContentInsert, 1, apVal[3+p->nColumn]);
+    if( rc!=SQLITE_OK ) return rc;
+  }
+
+  /* Execute the statement to insert the record. Set *piDocid to the 
+  ** new docid value. 
+  */
+  sqlite3_step(pContentInsert);
+  rc = sqlite3_reset(pContentInsert);
+
+  *piDocid = sqlite3_last_insert_rowid(p->db);
+  return rc;
+}
+
+
+
+/*
+** Remove all data from the FTS3 table. Clear the hash table containing
+** pending terms.
+*/
+static int fts3DeleteAll(Fts3Table *p, int bContent){
+  int rc = SQLITE_OK;             /* Return code */
+
+  /* Discard the contents of the pending-terms hash table. */
+  sqlite3Fts3PendingTermsClear(p);
+
+  /* Delete everything from the shadow tables. Except, leave %_content as
+  ** is if bContent is false.  */
+  assert( p->zContentTbl==0 || bContent==0 );
+  if( bContent ) fts3SqlExec(&rc, p, SQL_DELETE_ALL_CONTENT, 0);
+  fts3SqlExec(&rc, p, SQL_DELETE_ALL_SEGMENTS, 0);
+  fts3SqlExec(&rc, p, SQL_DELETE_ALL_SEGDIR, 0);
+  if( p->bHasDocsize ){
+    fts3SqlExec(&rc, p, SQL_DELETE_ALL_DOCSIZE, 0);
+  }
+  if( p->bHasStat ){
+    fts3SqlExec(&rc, p, SQL_DELETE_ALL_STAT, 0);
+  }
+  return rc;
+}
+
+/*
+**
+*/
+static int langidFromSelect(Fts3Table *p, sqlite3_stmt *pSelect){
+  int iLangid = 0;
+  if( p->zLanguageid ) iLangid = sqlite3_column_int(pSelect, p->nColumn+1);
+  return iLangid;
+}
+
+/*
+** The first element in the apVal[] array is assumed to contain the docid
+** (an integer) of a row about to be deleted. Remove all terms from the
+** full-text index.
+*/
+static void fts3DeleteTerms( 
+  int *pRC,               /* Result code */
+  Fts3Table *p,           /* The FTS table to delete from */
+  sqlite3_value *pRowid,  /* The docid to be deleted */
+  u32 *aSz,               /* Sizes of deleted document written here */
+  int *pbFound            /* OUT: Set to true if row really does exist */
+){
+  int rc;
+  sqlite3_stmt *pSelect;
+
+  assert( *pbFound==0 );
+  if( *pRC ) return;
+  rc = fts3SqlStmt(p, SQL_SELECT_CONTENT_BY_ROWID, &pSelect, &pRowid);
+  if( rc==SQLITE_OK ){
+    if( SQLITE_ROW==sqlite3_step(pSelect) ){
+      int i;
+      int iLangid = langidFromSelect(p, pSelect);
+      i64 iDocid = sqlite3_column_int64(pSelect, 0);
+      rc = fts3PendingTermsDocid(p, 1, iLangid, iDocid);
+      for(i=1; rc==SQLITE_OK && i<=p->nColumn; i++){
+        int iCol = i-1;
+        if( p->abNotindexed[iCol]==0 ){
+          const char *zText = (const char *)sqlite3_column_text(pSelect, i);
+          rc = fts3PendingTermsAdd(p, iLangid, zText, -1, &aSz[iCol]);
+          aSz[p->nColumn] += sqlite3_column_bytes(pSelect, i);
+        }
+      }
+      if( rc!=SQLITE_OK ){
+        sqlite3_reset(pSelect);
+        *pRC = rc;
+        return;
+      }
+      *pbFound = 1;
+    }
+    rc = sqlite3_reset(pSelect);
+  }else{
+    sqlite3_reset(pSelect);
+  }
+  *pRC = rc;
+}
+
+/*
+** Forward declaration to account for the circular dependency between
+** functions fts3SegmentMerge() and fts3AllocateSegdirIdx().
+*/
+static int fts3SegmentMerge(Fts3Table *, int, int, int);
+
+/* 
+** This function allocates a new level iLevel index in the segdir table.
+** Usually, indexes are allocated within a level sequentially starting
+** with 0, so the allocated index is one greater than the value returned
+** by:
+**
+**   SELECT max(idx) FROM %_segdir WHERE level = :iLevel
+**
+** However, if there are already FTS3_MERGE_COUNT indexes at the requested
+** level, they are merged into a single level (iLevel+1) segment and the 
+** allocated index is 0.
+**
+** If successful, *piIdx is set to the allocated index slot and SQLITE_OK
+** returned. Otherwise, an SQLite error code is returned.
+*/
+static int fts3AllocateSegdirIdx(
+  Fts3Table *p, 
+  int iLangid,                    /* Language id */
+  int iIndex,                     /* Index for p->aIndex */
+  int iLevel, 
+  int *piIdx
+){
+  int rc;                         /* Return Code */
+  sqlite3_stmt *pNextIdx;         /* Query for next idx at level iLevel */
+  int iNext = 0;                  /* Result of query pNextIdx */
+
+  assert( iLangid>=0 );
+  assert( p->nIndex>=1 );
+
+  /* Set variable iNext to the next available segdir index at level iLevel. */
+  rc = fts3SqlStmt(p, SQL_NEXT_SEGMENT_INDEX, &pNextIdx, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(
+        pNextIdx, 1, getAbsoluteLevel(p, iLangid, iIndex, iLevel)
+    );
+    if( SQLITE_ROW==sqlite3_step(pNextIdx) ){
+      iNext = sqlite3_column_int(pNextIdx, 0);
+    }
+    rc = sqlite3_reset(pNextIdx);
+  }
+
+  if( rc==SQLITE_OK ){
+    /* If iNext is FTS3_MERGE_COUNT, indicating that level iLevel is already
+    ** full, merge all segments in level iLevel into a single iLevel+1
+    ** segment and allocate (newly freed) index 0 at level iLevel. Otherwise,
+    ** if iNext is less than FTS3_MERGE_COUNT, allocate index iNext.
+    */
+    if( iNext>=FTS3_MERGE_COUNT ){
+      fts3LogMerge(16, getAbsoluteLevel(p, iLangid, iIndex, iLevel));
+      rc = fts3SegmentMerge(p, iLangid, iIndex, iLevel);
+      *piIdx = 0;
+    }else{
+      *piIdx = iNext;
+    }
+  }
+
+  return rc;
+}
+
+/*
+** The %_segments table is declared as follows:
+**
+**   CREATE TABLE %_segments(blockid INTEGER PRIMARY KEY, block BLOB)
+**
+** This function reads data from a single row of the %_segments table. The
+** specific row is identified by the iBlockid parameter. If paBlob is not
+** NULL, then a buffer is allocated using sqlite3_malloc() and populated
+** with the contents of the blob stored in the "block" column of the 
+** identified table row is. Whether or not paBlob is NULL, *pnBlob is set
+** to the size of the blob in bytes before returning.
+**
+** If an error occurs, or the table does not contain the specified row,
+** an SQLite error code is returned. Otherwise, SQLITE_OK is returned. If
+** paBlob is non-NULL, then it is the responsibility of the caller to
+** eventually free the returned buffer.
+**
+** This function may leave an open sqlite3_blob* handle in the
+** Fts3Table.pSegments variable. This handle is reused by subsequent calls
+** to this function. The handle may be closed by calling the
+** sqlite3Fts3SegmentsClose() function. Reusing a blob handle is a handy
+** performance improvement, but the blob handle should always be closed
+** before control is returned to the user (to prevent a lock being held
+** on the database file for longer than necessary). Thus, any virtual table
+** method (xFilter etc.) that may directly or indirectly call this function
+** must call sqlite3Fts3SegmentsClose() before returning.
+*/
+int sqlite3Fts3ReadBlock(
+  Fts3Table *p,                   /* FTS3 table handle */
+  sqlite3_int64 iBlockid,         /* Access the row with blockid=$iBlockid */
+  char **paBlob,                  /* OUT: Blob data in malloc'd buffer */
+  int *pnBlob,                    /* OUT: Size of blob data */
+  int *pnLoad                     /* OUT: Bytes actually loaded */
+){
+  int rc;                         /* Return code */
+
+  /* pnBlob must be non-NULL. paBlob may be NULL or non-NULL. */
+  assert( pnBlob );
+
+  if( p->pSegments ){
+    rc = sqlite3_blob_reopen(p->pSegments, iBlockid);
+  }else{
+    if( 0==p->zSegmentsTbl ){
+      p->zSegmentsTbl = sqlite3_mprintf("%s_segments", p->zName);
+      if( 0==p->zSegmentsTbl ) return SQLITE_NOMEM;
+    }
+    rc = sqlite3_blob_open(
+       p->db, p->zDb, p->zSegmentsTbl, "block", iBlockid, 0, &p->pSegments
+    );
+  }
+
+  if( rc==SQLITE_OK ){
+    int nByte = sqlite3_blob_bytes(p->pSegments);
+    *pnBlob = nByte;
+    if( paBlob ){
+      char *aByte = sqlite3_malloc(nByte + FTS3_NODE_PADDING);
+      if( !aByte ){
+        rc = SQLITE_NOMEM;
+      }else{
+        if( pnLoad && nByte>(FTS3_NODE_CHUNK_THRESHOLD) ){
+          nByte = FTS3_NODE_CHUNKSIZE;
+          *pnLoad = nByte;
+        }
+        rc = sqlite3_blob_read(p->pSegments, aByte, nByte, 0);
+        memset(&aByte[nByte], 0, FTS3_NODE_PADDING);
+        if( rc!=SQLITE_OK ){
+          sqlite3_free(aByte);
+          aByte = 0;
+        }
+      }
+      *paBlob = aByte;
+    }
+  }
+
+  return rc;
+}
+
+/*
+** Close the blob handle at p->pSegments, if it is open. See comments above
+** the sqlite3Fts3ReadBlock() function for details.
+*/
+void sqlite3Fts3SegmentsClose(Fts3Table *p){
+  sqlite3_blob_close(p->pSegments);
+  p->pSegments = 0;
+}
+    
+static int fts3SegReaderIncrRead(Fts3SegReader *pReader){
+  int nRead;                      /* Number of bytes to read */
+  int rc;                         /* Return code */
+
+  nRead = MIN(pReader->nNode - pReader->nPopulate, FTS3_NODE_CHUNKSIZE);
+  rc = sqlite3_blob_read(
+      pReader->pBlob, 
+      &pReader->aNode[pReader->nPopulate],
+      nRead,
+      pReader->nPopulate
+  );
+
+  if( rc==SQLITE_OK ){
+    pReader->nPopulate += nRead;
+    memset(&pReader->aNode[pReader->nPopulate], 0, FTS3_NODE_PADDING);
+    if( pReader->nPopulate==pReader->nNode ){
+      sqlite3_blob_close(pReader->pBlob);
+      pReader->pBlob = 0;
+      pReader->nPopulate = 0;
+    }
+  }
+  return rc;
+}
+
+static int fts3SegReaderRequire(Fts3SegReader *pReader, char *pFrom, int nByte){
+  int rc = SQLITE_OK;
+  assert( !pReader->pBlob 
+       || (pFrom>=pReader->aNode && pFrom<&pReader->aNode[pReader->nNode])
+  );
+  while( pReader->pBlob && rc==SQLITE_OK 
+     &&  (pFrom - pReader->aNode + nByte)>pReader->nPopulate
+  ){
+    rc = fts3SegReaderIncrRead(pReader);
+  }
+  return rc;
+}
+
+/*
+** Set an Fts3SegReader cursor to point at EOF.
+*/
+static void fts3SegReaderSetEof(Fts3SegReader *pSeg){
+  if( !fts3SegReaderIsRootOnly(pSeg) ){
+    sqlite3_free(pSeg->aNode);
+    sqlite3_blob_close(pSeg->pBlob);
+    pSeg->pBlob = 0;
+  }
+  pSeg->aNode = 0;
+}
+
+/*
+** Move the iterator passed as the first argument to the next term in the
+** segment. If successful, SQLITE_OK is returned. If there is no next term,
+** SQLITE_DONE. Otherwise, an SQLite error code.
+*/
+static int fts3SegReaderNext(
+  Fts3Table *p, 
+  Fts3SegReader *pReader,
+  int bIncr
+){
+  int rc;                         /* Return code of various sub-routines */
+  char *pNext;                    /* Cursor variable */
+  int nPrefix;                    /* Number of bytes in term prefix */
+  int nSuffix;                    /* Number of bytes in term suffix */
+
+  if( !pReader->aDoclist ){
+    pNext = pReader->aNode;
+  }else{
+    pNext = &pReader->aDoclist[pReader->nDoclist];
+  }
+
+  if( !pNext || pNext>=&pReader->aNode[pReader->nNode] ){
+
+    if( fts3SegReaderIsPending(pReader) ){
+      Fts3HashElem *pElem = *(pReader->ppNextElem);
+      sqlite3_free(pReader->aNode);
+      pReader->aNode = 0;
+      if( pElem ){
+        char *aCopy;
+        PendingList *pList = (PendingList *)fts3HashData(pElem);
+        int nCopy = pList->nData+1;
+        pReader->zTerm = (char *)fts3HashKey(pElem);
+        pReader->nTerm = fts3HashKeysize(pElem);
+        aCopy = (char*)sqlite3_malloc(nCopy);
+        if( !aCopy ) return SQLITE_NOMEM;
+        memcpy(aCopy, pList->aData, nCopy);
+        pReader->nNode = pReader->nDoclist = nCopy;
+        pReader->aNode = pReader->aDoclist = aCopy;
+        pReader->ppNextElem++;
+        assert( pReader->aNode );
+      }
+      return SQLITE_OK;
+    }
+
+    fts3SegReaderSetEof(pReader);
+
+    /* If iCurrentBlock>=iLeafEndBlock, this is an EOF condition. All leaf 
+    ** blocks have already been traversed.  */
+    assert( pReader->iCurrentBlock<=pReader->iLeafEndBlock );
+    if( pReader->iCurrentBlock>=pReader->iLeafEndBlock ){
+      return SQLITE_OK;
+    }
+
+    rc = sqlite3Fts3ReadBlock(
+        p, ++pReader->iCurrentBlock, &pReader->aNode, &pReader->nNode, 
+        (bIncr ? &pReader->nPopulate : 0)
+    );
+    if( rc!=SQLITE_OK ) return rc;
+    assert( pReader->pBlob==0 );
+    if( bIncr && pReader->nPopulate<pReader->nNode ){
+      pReader->pBlob = p->pSegments;
+      p->pSegments = 0;
+    }
+    pNext = pReader->aNode;
+  }
+
+  assert( !fts3SegReaderIsPending(pReader) );
+
+  rc = fts3SegReaderRequire(pReader, pNext, FTS3_VARINT_MAX*2);
+  if( rc!=SQLITE_OK ) return rc;
+  
+  /* Because of the FTS3_NODE_PADDING bytes of padding, the following is 
+  ** safe (no risk of overread) even if the node data is corrupted. */
+  pNext += fts3GetVarint32(pNext, &nPrefix);
+  pNext += fts3GetVarint32(pNext, &nSuffix);
+  if( nPrefix<0 || nSuffix<=0 
+   || &pNext[nSuffix]>&pReader->aNode[pReader->nNode] 
+  ){
+    return FTS_CORRUPT_VTAB;
+  }
+
+  if( nPrefix+nSuffix>pReader->nTermAlloc ){
+    int nNew = (nPrefix+nSuffix)*2;
+    char *zNew = sqlite3_realloc(pReader->zTerm, nNew);
+    if( !zNew ){
+      return SQLITE_NOMEM;
+    }
+    pReader->zTerm = zNew;
+    pReader->nTermAlloc = nNew;
+  }
+
+  rc = fts3SegReaderRequire(pReader, pNext, nSuffix+FTS3_VARINT_MAX);
+  if( rc!=SQLITE_OK ) return rc;
+
+  memcpy(&pReader->zTerm[nPrefix], pNext, nSuffix);
+  pReader->nTerm = nPrefix+nSuffix;
+  pNext += nSuffix;
+  pNext += fts3GetVarint32(pNext, &pReader->nDoclist);
+  pReader->aDoclist = pNext;
+  pReader->pOffsetList = 0;
+
+  /* Check that the doclist does not appear to extend past the end of the
+  ** b-tree node. And that the final byte of the doclist is 0x00. If either 
+  ** of these statements is untrue, then the data structure is corrupt.
+  */
+  if( &pReader->aDoclist[pReader->nDoclist]>&pReader->aNode[pReader->nNode] 
+   || (pReader->nPopulate==0 && pReader->aDoclist[pReader->nDoclist-1])
+  ){
+    return FTS_CORRUPT_VTAB;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Set the SegReader to point to the first docid in the doclist associated
+** with the current term.
+*/
+static int fts3SegReaderFirstDocid(Fts3Table *pTab, Fts3SegReader *pReader){
+  int rc = SQLITE_OK;
+  assert( pReader->aDoclist );
+  assert( !pReader->pOffsetList );
+  if( pTab->bDescIdx && fts3SegReaderIsPending(pReader) ){
+    u8 bEof = 0;
+    pReader->iDocid = 0;
+    pReader->nOffsetList = 0;
+    sqlite3Fts3DoclistPrev(0,
+        pReader->aDoclist, pReader->nDoclist, &pReader->pOffsetList, 
+        &pReader->iDocid, &pReader->nOffsetList, &bEof
+    );
+  }else{
+    rc = fts3SegReaderRequire(pReader, pReader->aDoclist, FTS3_VARINT_MAX);
+    if( rc==SQLITE_OK ){
+      int n = sqlite3Fts3GetVarint(pReader->aDoclist, &pReader->iDocid);
+      pReader->pOffsetList = &pReader->aDoclist[n];
+    }
+  }
+  return rc;
+}
+
+/*
+** Advance the SegReader to point to the next docid in the doclist
+** associated with the current term.
+** 
+** If arguments ppOffsetList and pnOffsetList are not NULL, then 
+** *ppOffsetList is set to point to the first column-offset list
+** in the doclist entry (i.e. immediately past the docid varint).
+** *pnOffsetList is set to the length of the set of column-offset
+** lists, not including the nul-terminator byte. For example:
+*/
+static int fts3SegReaderNextDocid(
+  Fts3Table *pTab,
+  Fts3SegReader *pReader,         /* Reader to advance to next docid */
+  char **ppOffsetList,            /* OUT: Pointer to current position-list */
+  int *pnOffsetList               /* OUT: Length of *ppOffsetList in bytes */
+){
+  int rc = SQLITE_OK;
+  char *p = pReader->pOffsetList;
+  char c = 0;
+
+  assert( p );
+
+  if( pTab->bDescIdx && fts3SegReaderIsPending(pReader) ){
+    /* A pending-terms seg-reader for an FTS4 table that uses order=desc.
+    ** Pending-terms doclists are always built up in ascending order, so
+    ** we have to iterate through them backwards here. */
+    u8 bEof = 0;
+    if( ppOffsetList ){
+      *ppOffsetList = pReader->pOffsetList;
+      *pnOffsetList = pReader->nOffsetList - 1;
+    }
+    sqlite3Fts3DoclistPrev(0,
+        pReader->aDoclist, pReader->nDoclist, &p, &pReader->iDocid,
+        &pReader->nOffsetList, &bEof
+    );
+    if( bEof ){
+      pReader->pOffsetList = 0;
+    }else{
+      pReader->pOffsetList = p;
+    }
+  }else{
+    char *pEnd = &pReader->aDoclist[pReader->nDoclist];
+
+    /* Pointer p currently points at the first byte of an offset list. The
+    ** following block advances it to point one byte past the end of
+    ** the same offset list. */
+    while( 1 ){
+  
+      /* The following line of code (and the "p++" below the while() loop) is
+      ** normally all that is required to move pointer p to the desired 
+      ** position. The exception is if this node is being loaded from disk
+      ** incrementally and pointer "p" now points to the first byte past
+      ** the populated part of pReader->aNode[].
+      */
+      while( *p | c ) c = *p++ & 0x80;
+      assert( *p==0 );
+  
+      if( pReader->pBlob==0 || p<&pReader->aNode[pReader->nPopulate] ) break;
+      rc = fts3SegReaderIncrRead(pReader);
+      if( rc!=SQLITE_OK ) return rc;
+    }
+    p++;
+  
+    /* If required, populate the output variables with a pointer to and the
+    ** size of the previous offset-list.
+    */
+    if( ppOffsetList ){
+      *ppOffsetList = pReader->pOffsetList;
+      *pnOffsetList = (int)(p - pReader->pOffsetList - 1);
+    }
+
+    /* List may have been edited in place by fts3EvalNearTrim() */
+    while( p<pEnd && *p==0 ) p++;
+  
+    /* If there are no more entries in the doclist, set pOffsetList to
+    ** NULL. Otherwise, set Fts3SegReader.iDocid to the next docid and
+    ** Fts3SegReader.pOffsetList to point to the next offset list before
+    ** returning.
+    */
+    if( p>=pEnd ){
+      pReader->pOffsetList = 0;
+    }else{
+      rc = fts3SegReaderRequire(pReader, p, FTS3_VARINT_MAX);
+      if( rc==SQLITE_OK ){
+        sqlite3_int64 iDelta;
+        pReader->pOffsetList = p + sqlite3Fts3GetVarint(p, &iDelta);
+        if( pTab->bDescIdx ){
+          pReader->iDocid -= iDelta;
+        }else{
+          pReader->iDocid += iDelta;
+        }
+      }
+    }
+  }
+
+  return SQLITE_OK;
+}
+
+
+int sqlite3Fts3MsrOvfl(
+  Fts3Cursor *pCsr, 
+  Fts3MultiSegReader *pMsr,
+  int *pnOvfl
+){
+  Fts3Table *p = (Fts3Table*)pCsr->base.pVtab;
+  int nOvfl = 0;
+  int ii;
+  int rc = SQLITE_OK;
+  int pgsz = p->nPgsz;
+
+  assert( p->bFts4 );
+  assert( pgsz>0 );
+
+  for(ii=0; rc==SQLITE_OK && ii<pMsr->nSegment; ii++){
+    Fts3SegReader *pReader = pMsr->apSegment[ii];
+    if( !fts3SegReaderIsPending(pReader) 
+     && !fts3SegReaderIsRootOnly(pReader) 
+    ){
+      sqlite3_int64 jj;
+      for(jj=pReader->iStartBlock; jj<=pReader->iLeafEndBlock; jj++){
+        int nBlob;
+        rc = sqlite3Fts3ReadBlock(p, jj, 0, &nBlob, 0);
+        if( rc!=SQLITE_OK ) break;
+        if( (nBlob+35)>pgsz ){
+          nOvfl += (nBlob + 34)/pgsz;
+        }
+      }
+    }
+  }
+  *pnOvfl = nOvfl;
+  return rc;
+}
+
+/*
+** Free all allocations associated with the iterator passed as the 
+** second argument.
+*/
+void sqlite3Fts3SegReaderFree(Fts3SegReader *pReader){
+  if( pReader ){
+    if( !fts3SegReaderIsPending(pReader) ){
+      sqlite3_free(pReader->zTerm);
+    }
+    if( !fts3SegReaderIsRootOnly(pReader) ){
+      sqlite3_free(pReader->aNode);
+    }
+    sqlite3_blob_close(pReader->pBlob);
+  }
+  sqlite3_free(pReader);
+}
+
+/*
+** Allocate a new SegReader object.
+*/
+int sqlite3Fts3SegReaderNew(
+  int iAge,                       /* Segment "age". */
+  int bLookup,                    /* True for a lookup only */
+  sqlite3_int64 iStartLeaf,       /* First leaf to traverse */
+  sqlite3_int64 iEndLeaf,         /* Final leaf to traverse */
+  sqlite3_int64 iEndBlock,        /* Final block of segment */
+  const char *zRoot,              /* Buffer containing root node */
+  int nRoot,                      /* Size of buffer containing root node */
+  Fts3SegReader **ppReader        /* OUT: Allocated Fts3SegReader */
+){
+  Fts3SegReader *pReader;         /* Newly allocated SegReader object */
+  int nExtra = 0;                 /* Bytes to allocate segment root node */
+
+  assert( iStartLeaf<=iEndLeaf );
+  if( iStartLeaf==0 ){
+    nExtra = nRoot + FTS3_NODE_PADDING;
+  }
+
+  pReader = (Fts3SegReader *)sqlite3_malloc(sizeof(Fts3SegReader) + nExtra);
+  if( !pReader ){
+    return SQLITE_NOMEM;
+  }
+  memset(pReader, 0, sizeof(Fts3SegReader));
+  pReader->iIdx = iAge;
+  pReader->bLookup = bLookup!=0;
+  pReader->iStartBlock = iStartLeaf;
+  pReader->iLeafEndBlock = iEndLeaf;
+  pReader->iEndBlock = iEndBlock;
+
+  if( nExtra ){
+    /* The entire segment is stored in the root node. */
+    pReader->aNode = (char *)&pReader[1];
+    pReader->rootOnly = 1;
+    pReader->nNode = nRoot;
+    memcpy(pReader->aNode, zRoot, nRoot);
+    memset(&pReader->aNode[nRoot], 0, FTS3_NODE_PADDING);
+  }else{
+    pReader->iCurrentBlock = iStartLeaf-1;
+  }
+  *ppReader = pReader;
+  return SQLITE_OK;
+}
+
+/*
+** This is a comparison function used as a qsort() callback when sorting
+** an array of pending terms by term. This occurs as part of flushing
+** the contents of the pending-terms hash table to the database.
+*/
+static int SQLITE_CDECL fts3CompareElemByTerm(
+  const void *lhs,
+  const void *rhs
+){
+  char *z1 = fts3HashKey(*(Fts3HashElem **)lhs);
+  char *z2 = fts3HashKey(*(Fts3HashElem **)rhs);
+  int n1 = fts3HashKeysize(*(Fts3HashElem **)lhs);
+  int n2 = fts3HashKeysize(*(Fts3HashElem **)rhs);
+
+  int n = (n1<n2 ? n1 : n2);
+  int c = memcmp(z1, z2, n);
+  if( c==0 ){
+    c = n1 - n2;
+  }
+  return c;
+}
+
+/*
+** This function is used to allocate an Fts3SegReader that iterates through
+** a subset of the terms stored in the Fts3Table.pendingTerms array.
+**
+** If the isPrefixIter parameter is zero, then the returned SegReader iterates
+** through each term in the pending-terms table. Or, if isPrefixIter is
+** non-zero, it iterates through each term and its prefixes. For example, if
+** the pending terms hash table contains the terms "sqlite", "mysql" and
+** "firebird", then the iterator visits the following 'terms' (in the order
+** shown):
+**
+**   f fi fir fire fireb firebi firebir firebird
+**   m my mys mysq mysql
+**   s sq sql sqli sqlit sqlite
+**
+** Whereas if isPrefixIter is zero, the terms visited are:
+**
+**   firebird mysql sqlite
+*/
+int sqlite3Fts3SegReaderPending(
+  Fts3Table *p,                   /* Virtual table handle */
+  int iIndex,                     /* Index for p->aIndex */
+  const char *zTerm,              /* Term to search for */
+  int nTerm,                      /* Size of buffer zTerm */
+  int bPrefix,                    /* True for a prefix iterator */
+  Fts3SegReader **ppReader        /* OUT: SegReader for pending-terms */
+){
+  Fts3SegReader *pReader = 0;     /* Fts3SegReader object to return */
+  Fts3HashElem *pE;               /* Iterator variable */
+  Fts3HashElem **aElem = 0;       /* Array of term hash entries to scan */
+  int nElem = 0;                  /* Size of array at aElem */
+  int rc = SQLITE_OK;             /* Return Code */
+  Fts3Hash *pHash;
+
+  pHash = &p->aIndex[iIndex].hPending;
+  if( bPrefix ){
+    int nAlloc = 0;               /* Size of allocated array at aElem */
+
+    for(pE=fts3HashFirst(pHash); pE; pE=fts3HashNext(pE)){
+      char *zKey = (char *)fts3HashKey(pE);
+      int nKey = fts3HashKeysize(pE);
+      if( nTerm==0 || (nKey>=nTerm && 0==memcmp(zKey, zTerm, nTerm)) ){
+        if( nElem==nAlloc ){
+          Fts3HashElem **aElem2;
+          nAlloc += 16;
+          aElem2 = (Fts3HashElem **)sqlite3_realloc(
+              aElem, nAlloc*sizeof(Fts3HashElem *)
+          );
+          if( !aElem2 ){
+            rc = SQLITE_NOMEM;
+            nElem = 0;
+            break;
+          }
+          aElem = aElem2;
+        }
+
+        aElem[nElem++] = pE;
+      }
+    }
+
+    /* If more than one term matches the prefix, sort the Fts3HashElem
+    ** objects in term order using qsort(). This uses the same comparison
+    ** callback as is used when flushing terms to disk.
+    */
+    if( nElem>1 ){
+      qsort(aElem, nElem, sizeof(Fts3HashElem *), fts3CompareElemByTerm);
+    }
+
+  }else{
+    /* The query is a simple term lookup that matches at most one term in
+    ** the index. All that is required is a straight hash-lookup. 
+    **
+    ** Because the stack address of pE may be accessed via the aElem pointer
+    ** below, the "Fts3HashElem *pE" must be declared so that it is valid
+    ** within this entire function, not just this "else{...}" block.
+    */
+    pE = fts3HashFindElem(pHash, zTerm, nTerm);
+    if( pE ){
+      aElem = &pE;
+      nElem = 1;
+    }
+  }
+
+  if( nElem>0 ){
+    int nByte = sizeof(Fts3SegReader) + (nElem+1)*sizeof(Fts3HashElem *);
+    pReader = (Fts3SegReader *)sqlite3_malloc(nByte);
+    if( !pReader ){
+      rc = SQLITE_NOMEM;
+    }else{
+      memset(pReader, 0, nByte);
+      pReader->iIdx = 0x7FFFFFFF;
+      pReader->ppNextElem = (Fts3HashElem **)&pReader[1];
+      memcpy(pReader->ppNextElem, aElem, nElem*sizeof(Fts3HashElem *));
+    }
+  }
+
+  if( bPrefix ){
+    sqlite3_free(aElem);
+  }
+  *ppReader = pReader;
+  return rc;
+}
+
+/*
+** Compare the entries pointed to by two Fts3SegReader structures. 
+** Comparison is as follows:
+**
+**   1) EOF is greater than not EOF.
+**
+**   2) The current terms (if any) are compared using memcmp(). If one
+**      term is a prefix of another, the longer term is considered the
+**      larger.
+**
+**   3) By segment age. An older segment is considered larger.
+*/
+static int fts3SegReaderCmp(Fts3SegReader *pLhs, Fts3SegReader *pRhs){
+  int rc;
+  if( pLhs->aNode && pRhs->aNode ){
+    int rc2 = pLhs->nTerm - pRhs->nTerm;
+    if( rc2<0 ){
+      rc = memcmp(pLhs->zTerm, pRhs->zTerm, pLhs->nTerm);
+    }else{
+      rc = memcmp(pLhs->zTerm, pRhs->zTerm, pRhs->nTerm);
+    }
+    if( rc==0 ){
+      rc = rc2;
+    }
+  }else{
+    rc = (pLhs->aNode==0) - (pRhs->aNode==0);
+  }
+  if( rc==0 ){
+    rc = pRhs->iIdx - pLhs->iIdx;
+  }
+  assert( rc!=0 );
+  return rc;
+}
+
+/*
+** A different comparison function for SegReader structures. In this
+** version, it is assumed that each SegReader points to an entry in
+** a doclist for identical terms. Comparison is made as follows:
+**
+**   1) EOF (end of doclist in this case) is greater than not EOF.
+**
+**   2) By current docid.
+**
+**   3) By segment age. An older segment is considered larger.
+*/
+static int fts3SegReaderDoclistCmp(Fts3SegReader *pLhs, Fts3SegReader *pRhs){
+  int rc = (pLhs->pOffsetList==0)-(pRhs->pOffsetList==0);
+  if( rc==0 ){
+    if( pLhs->iDocid==pRhs->iDocid ){
+      rc = pRhs->iIdx - pLhs->iIdx;
+    }else{
+      rc = (pLhs->iDocid > pRhs->iDocid) ? 1 : -1;
+    }
+  }
+  assert( pLhs->aNode && pRhs->aNode );
+  return rc;
+}
+static int fts3SegReaderDoclistCmpRev(Fts3SegReader *pLhs, Fts3SegReader *pRhs){
+  int rc = (pLhs->pOffsetList==0)-(pRhs->pOffsetList==0);
+  if( rc==0 ){
+    if( pLhs->iDocid==pRhs->iDocid ){
+      rc = pRhs->iIdx - pLhs->iIdx;
+    }else{
+      rc = (pLhs->iDocid < pRhs->iDocid) ? 1 : -1;
+    }
+  }
+  assert( pLhs->aNode && pRhs->aNode );
+  return rc;
+}
+
+/*
+** Compare the term that the Fts3SegReader object passed as the first argument
+** points to with the term specified by arguments zTerm and nTerm. 
+**
+** If the pSeg iterator is already at EOF, return 0. Otherwise, return
+** -ve if the pSeg term is less than zTerm/nTerm, 0 if the two terms are
+** equal, or +ve if the pSeg term is greater than zTerm/nTerm.
+*/
+static int fts3SegReaderTermCmp(
+  Fts3SegReader *pSeg,            /* Segment reader object */
+  const char *zTerm,              /* Term to compare to */
+  int nTerm                       /* Size of term zTerm in bytes */
+){
+  int res = 0;
+  if( pSeg->aNode ){
+    if( pSeg->nTerm>nTerm ){
+      res = memcmp(pSeg->zTerm, zTerm, nTerm);
+    }else{
+      res = memcmp(pSeg->zTerm, zTerm, pSeg->nTerm);
+    }
+    if( res==0 ){
+      res = pSeg->nTerm-nTerm;
+    }
+  }
+  return res;
+}
+
+/*
+** Argument apSegment is an array of nSegment elements. It is known that
+** the final (nSegment-nSuspect) members are already in sorted order
+** (according to the comparison function provided). This function shuffles
+** the array around until all entries are in sorted order.
+*/
+static void fts3SegReaderSort(
+  Fts3SegReader **apSegment,                     /* Array to sort entries of */
+  int nSegment,                                  /* Size of apSegment array */
+  int nSuspect,                                  /* Unsorted entry count */
+  int (*xCmp)(Fts3SegReader *, Fts3SegReader *)  /* Comparison function */
+){
+  int i;                          /* Iterator variable */
+
+  assert( nSuspect<=nSegment );
+
+  if( nSuspect==nSegment ) nSuspect--;
+  for(i=nSuspect-1; i>=0; i--){
+    int j;
+    for(j=i; j<(nSegment-1); j++){
+      Fts3SegReader *pTmp;
+      if( xCmp(apSegment[j], apSegment[j+1])<0 ) break;
+      pTmp = apSegment[j+1];
+      apSegment[j+1] = apSegment[j];
+      apSegment[j] = pTmp;
+    }
+  }
+
+#ifndef NDEBUG
+  /* Check that the list really is sorted now. */
+  for(i=0; i<(nSuspect-1); i++){
+    assert( xCmp(apSegment[i], apSegment[i+1])<0 );
+  }
+#endif
+}
+
+/* 
+** Insert a record into the %_segments table.
+*/
+static int fts3WriteSegment(
+  Fts3Table *p,                   /* Virtual table handle */
+  sqlite3_int64 iBlock,           /* Block id for new block */
+  char *z,                        /* Pointer to buffer containing block data */
+  int n                           /* Size of buffer z in bytes */
+){
+  sqlite3_stmt *pStmt;
+  int rc = fts3SqlStmt(p, SQL_INSERT_SEGMENTS, &pStmt, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pStmt, 1, iBlock);
+    sqlite3_bind_blob(pStmt, 2, z, n, SQLITE_STATIC);
+    sqlite3_step(pStmt);
+    rc = sqlite3_reset(pStmt);
+  }
+  return rc;
+}
+
+/*
+** Find the largest relative level number in the table. If successful, set
+** *pnMax to this value and return SQLITE_OK. Otherwise, if an error occurs,
+** set *pnMax to zero and return an SQLite error code.
+*/
+int sqlite3Fts3MaxLevel(Fts3Table *p, int *pnMax){
+  int rc;
+  int mxLevel = 0;
+  sqlite3_stmt *pStmt = 0;
+
+  rc = fts3SqlStmt(p, SQL_SELECT_MXLEVEL, &pStmt, 0);
+  if( rc==SQLITE_OK ){
+    if( SQLITE_ROW==sqlite3_step(pStmt) ){
+      mxLevel = sqlite3_column_int(pStmt, 0);
+    }
+    rc = sqlite3_reset(pStmt);
+  }
+  *pnMax = mxLevel;
+  return rc;
+}
+
+/* 
+** Insert a record into the %_segdir table.
+*/
+static int fts3WriteSegdir(
+  Fts3Table *p,                   /* Virtual table handle */
+  sqlite3_int64 iLevel,           /* Value for "level" field (absolute level) */
+  int iIdx,                       /* Value for "idx" field */
+  sqlite3_int64 iStartBlock,      /* Value for "start_block" field */
+  sqlite3_int64 iLeafEndBlock,    /* Value for "leaves_end_block" field */
+  sqlite3_int64 iEndBlock,        /* Value for "end_block" field */
+  sqlite3_int64 nLeafData,        /* Bytes of leaf data in segment */
+  char *zRoot,                    /* Blob value for "root" field */
+  int nRoot                       /* Number of bytes in buffer zRoot */
+){
+  sqlite3_stmt *pStmt;
+  int rc = fts3SqlStmt(p, SQL_INSERT_SEGDIR, &pStmt, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pStmt, 1, iLevel);
+    sqlite3_bind_int(pStmt, 2, iIdx);
+    sqlite3_bind_int64(pStmt, 3, iStartBlock);
+    sqlite3_bind_int64(pStmt, 4, iLeafEndBlock);
+    if( nLeafData==0 ){
+      sqlite3_bind_int64(pStmt, 5, iEndBlock);
+    }else{
+      char *zEnd = sqlite3_mprintf("%lld %lld", iEndBlock, nLeafData);
+      if( !zEnd ) return SQLITE_NOMEM;
+      sqlite3_bind_text(pStmt, 5, zEnd, -1, sqlite3_free);
+    }
+    sqlite3_bind_blob(pStmt, 6, zRoot, nRoot, SQLITE_STATIC);
+    sqlite3_step(pStmt);
+    rc = sqlite3_reset(pStmt);
+  }
+  return rc;
+}
+
+/*
+** Return the size of the common prefix (if any) shared by zPrev and
+** zNext, in bytes. For example, 
+**
+**   fts3PrefixCompress("abc", 3, "abcdef", 6)   // returns 3
+**   fts3PrefixCompress("abX", 3, "abcdef", 6)   // returns 2
+**   fts3PrefixCompress("abX", 3, "Xbcdef", 6)   // returns 0
+*/
+static int fts3PrefixCompress(
+  const char *zPrev,              /* Buffer containing previous term */
+  int nPrev,                      /* Size of buffer zPrev in bytes */
+  const char *zNext,              /* Buffer containing next term */
+  int nNext                       /* Size of buffer zNext in bytes */
+){
+  int n;
+  UNUSED_PARAMETER(nNext);
+  for(n=0; n<nPrev && zPrev[n]==zNext[n]; n++);
+  return n;
+}
+
+/*
+** Add term zTerm to the SegmentNode. It is guaranteed that zTerm is larger
+** (according to memcmp) than the previous term.
+*/
+static int fts3NodeAddTerm(
+  Fts3Table *p,                   /* Virtual table handle */
+  SegmentNode **ppTree,           /* IN/OUT: SegmentNode handle */ 
+  int isCopyTerm,                 /* True if zTerm/nTerm is transient */
+  const char *zTerm,              /* Pointer to buffer containing term */
+  int nTerm                       /* Size of term in bytes */
+){
+  SegmentNode *pTree = *ppTree;
+  int rc;
+  SegmentNode *pNew;
+
+  /* First try to append the term to the current node. Return early if 
+  ** this is possible.
+  */
+  if( pTree ){
+    int nData = pTree->nData;     /* Current size of node in bytes */
+    int nReq = nData;             /* Required space after adding zTerm */
+    int nPrefix;                  /* Number of bytes of prefix compression */
+    int nSuffix;                  /* Suffix length */
+
+    nPrefix = fts3PrefixCompress(pTree->zTerm, pTree->nTerm, zTerm, nTerm);
+    nSuffix = nTerm-nPrefix;
+
+    nReq += sqlite3Fts3VarintLen(nPrefix)+sqlite3Fts3VarintLen(nSuffix)+nSuffix;
+    if( nReq<=p->nNodeSize || !pTree->zTerm ){
+
+      if( nReq>p->nNodeSize ){
+        /* An unusual case: this is the first term to be added to the node
+        ** and the static node buffer (p->nNodeSize bytes) is not large
+        ** enough. Use a separately malloced buffer instead This wastes
+        ** p->nNodeSize bytes, but since this scenario only comes about when
+        ** the database contain two terms that share a prefix of almost 2KB, 
+        ** this is not expected to be a serious problem. 
+        */
+        assert( pTree->aData==(char *)&pTree[1] );
+        pTree->aData = (char *)sqlite3_malloc(nReq);
+        if( !pTree->aData ){
+          return SQLITE_NOMEM;
+        }
+      }
+
+      if( pTree->zTerm ){
+        /* There is no prefix-length field for first term in a node */
+        nData += sqlite3Fts3PutVarint(&pTree->aData[nData], nPrefix);
+      }
+
+      nData += sqlite3Fts3PutVarint(&pTree->aData[nData], nSuffix);
+      memcpy(&pTree->aData[nData], &zTerm[nPrefix], nSuffix);
+      pTree->nData = nData + nSuffix;
+      pTree->nEntry++;
+
+      if( isCopyTerm ){
+        if( pTree->nMalloc<nTerm ){
+          char *zNew = sqlite3_realloc(pTree->zMalloc, nTerm*2);
+          if( !zNew ){
+            return SQLITE_NOMEM;
+          }
+          pTree->nMalloc = nTerm*2;
+          pTree->zMalloc = zNew;
+        }
+        pTree->zTerm = pTree->zMalloc;
+        memcpy(pTree->zTerm, zTerm, nTerm);
+        pTree->nTerm = nTerm;
+      }else{
+        pTree->zTerm = (char *)zTerm;
+        pTree->nTerm = nTerm;
+      }
+      return SQLITE_OK;
+    }
+  }
+
+  /* If control flows to here, it was not possible to append zTerm to the
+  ** current node. Create a new node (a right-sibling of the current node).
+  ** If this is the first node in the tree, the term is added to it.
+  **
+  ** Otherwise, the term is not added to the new node, it is left empty for
+  ** now. Instead, the term is inserted into the parent of pTree. If pTree 
+  ** has no parent, one is created here.
+  */
+  pNew = (SegmentNode *)sqlite3_malloc(sizeof(SegmentNode) + p->nNodeSize);
+  if( !pNew ){
+    return SQLITE_NOMEM;
+  }
+  memset(pNew, 0, sizeof(SegmentNode));
+  pNew->nData = 1 + FTS3_VARINT_MAX;
+  pNew->aData = (char *)&pNew[1];
+
+  if( pTree ){
+    SegmentNode *pParent = pTree->pParent;
+    rc = fts3NodeAddTerm(p, &pParent, isCopyTerm, zTerm, nTerm);
+    if( pTree->pParent==0 ){
+      pTree->pParent = pParent;
+    }
+    pTree->pRight = pNew;
+    pNew->pLeftmost = pTree->pLeftmost;
+    pNew->pParent = pParent;
+    pNew->zMalloc = pTree->zMalloc;
+    pNew->nMalloc = pTree->nMalloc;
+    pTree->zMalloc = 0;
+  }else{
+    pNew->pLeftmost = pNew;
+    rc = fts3NodeAddTerm(p, &pNew, isCopyTerm, zTerm, nTerm); 
+  }
+
+  *ppTree = pNew;
+  return rc;
+}
+
+/*
+** Helper function for fts3NodeWrite().
+*/
+static int fts3TreeFinishNode(
+  SegmentNode *pTree, 
+  int iHeight, 
+  sqlite3_int64 iLeftChild
+){
+  int nStart;
+  assert( iHeight>=1 && iHeight<128 );
+  nStart = FTS3_VARINT_MAX - sqlite3Fts3VarintLen(iLeftChild);
+  pTree->aData[nStart] = (char)iHeight;
+  sqlite3Fts3PutVarint(&pTree->aData[nStart+1], iLeftChild);
+  return nStart;
+}
+
+/*
+** Write the buffer for the segment node pTree and all of its peers to the
+** database. Then call this function recursively to write the parent of 
+** pTree and its peers to the database. 
+**
+** Except, if pTree is a root node, do not write it to the database. Instead,
+** set output variables *paRoot and *pnRoot to contain the root node.
+**
+** If successful, SQLITE_OK is returned and output variable *piLast is
+** set to the largest blockid written to the database (or zero if no
+** blocks were written to the db). Otherwise, an SQLite error code is 
+** returned.
+*/
+static int fts3NodeWrite(
+  Fts3Table *p,                   /* Virtual table handle */
+  SegmentNode *pTree,             /* SegmentNode handle */
+  int iHeight,                    /* Height of this node in tree */
+  sqlite3_int64 iLeaf,            /* Block id of first leaf node */
+  sqlite3_int64 iFree,            /* Block id of next free slot in %_segments */
+  sqlite3_int64 *piLast,          /* OUT: Block id of last entry written */
+  char **paRoot,                  /* OUT: Data for root node */
+  int *pnRoot                     /* OUT: Size of root node in bytes */
+){
+  int rc = SQLITE_OK;
+
+  if( !pTree->pParent ){
+    /* Root node of the tree. */
+    int nStart = fts3TreeFinishNode(pTree, iHeight, iLeaf);
+    *piLast = iFree-1;
+    *pnRoot = pTree->nData - nStart;
+    *paRoot = &pTree->aData[nStart];
+  }else{
+    SegmentNode *pIter;
+    sqlite3_int64 iNextFree = iFree;
+    sqlite3_int64 iNextLeaf = iLeaf;
+    for(pIter=pTree->pLeftmost; pIter && rc==SQLITE_OK; pIter=pIter->pRight){
+      int nStart = fts3TreeFinishNode(pIter, iHeight, iNextLeaf);
+      int nWrite = pIter->nData - nStart;
+  
+      rc = fts3WriteSegment(p, iNextFree, &pIter->aData[nStart], nWrite);
+      iNextFree++;
+      iNextLeaf += (pIter->nEntry+1);
+    }
+    if( rc==SQLITE_OK ){
+      assert( iNextLeaf==iFree );
+      rc = fts3NodeWrite(
+          p, pTree->pParent, iHeight+1, iFree, iNextFree, piLast, paRoot, pnRoot
+      );
+    }
+  }
+
+  return rc;
+}
+
+/*
+** Free all memory allocations associated with the tree pTree.
+*/
+static void fts3NodeFree(SegmentNode *pTree){
+  if( pTree ){
+    SegmentNode *p = pTree->pLeftmost;
+    fts3NodeFree(p->pParent);
+    while( p ){
+      SegmentNode *pRight = p->pRight;
+      if( p->aData!=(char *)&p[1] ){
+        sqlite3_free(p->aData);
+      }
+      assert( pRight==0 || p->zMalloc==0 );
+      sqlite3_free(p->zMalloc);
+      sqlite3_free(p);
+      p = pRight;
+    }
+  }
+}
+
+/*
+** Add a term to the segment being constructed by the SegmentWriter object
+** *ppWriter. When adding the first term to a segment, *ppWriter should
+** be passed NULL. This function will allocate a new SegmentWriter object
+** and return it via the input/output variable *ppWriter in this case.
+**
+** If successful, SQLITE_OK is returned. Otherwise, an SQLite error code.
+*/
+static int fts3SegWriterAdd(
+  Fts3Table *p,                   /* Virtual table handle */
+  SegmentWriter **ppWriter,       /* IN/OUT: SegmentWriter handle */ 
+  int isCopyTerm,                 /* True if buffer zTerm must be copied */
+  const char *zTerm,              /* Pointer to buffer containing term */
+  int nTerm,                      /* Size of term in bytes */
+  const char *aDoclist,           /* Pointer to buffer containing doclist */
+  int nDoclist                    /* Size of doclist in bytes */
+){
+  int nPrefix;                    /* Size of term prefix in bytes */
+  int nSuffix;                    /* Size of term suffix in bytes */
+  int nReq;                       /* Number of bytes required on leaf page */
+  int nData;
+  SegmentWriter *pWriter = *ppWriter;
+
+  if( !pWriter ){
+    int rc;
+    sqlite3_stmt *pStmt;
+
+    /* Allocate the SegmentWriter structure */
+    pWriter = (SegmentWriter *)sqlite3_malloc(sizeof(SegmentWriter));
+    if( !pWriter ) return SQLITE_NOMEM;
+    memset(pWriter, 0, sizeof(SegmentWriter));
+    *ppWriter = pWriter;
+
+    /* Allocate a buffer in which to accumulate data */
+    pWriter->aData = (char *)sqlite3_malloc(p->nNodeSize);
+    if( !pWriter->aData ) return SQLITE_NOMEM;
+    pWriter->nSize = p->nNodeSize;
+
+    /* Find the next free blockid in the %_segments table */
+    rc = fts3SqlStmt(p, SQL_NEXT_SEGMENTS_ID, &pStmt, 0);
+    if( rc!=SQLITE_OK ) return rc;
+    if( SQLITE_ROW==sqlite3_step(pStmt) ){
+      pWriter->iFree = sqlite3_column_int64(pStmt, 0);
+      pWriter->iFirst = pWriter->iFree;
+    }
+    rc = sqlite3_reset(pStmt);
+    if( rc!=SQLITE_OK ) return rc;
+  }
+  nData = pWriter->nData;
+
+  nPrefix = fts3PrefixCompress(pWriter->zTerm, pWriter->nTerm, zTerm, nTerm);
+  nSuffix = nTerm-nPrefix;
+
+  /* Figure out how many bytes are required by this new entry */
+  nReq = sqlite3Fts3VarintLen(nPrefix) +    /* varint containing prefix size */
+    sqlite3Fts3VarintLen(nSuffix) +         /* varint containing suffix size */
+    nSuffix +                               /* Term suffix */
+    sqlite3Fts3VarintLen(nDoclist) +        /* Size of doclist */
+    nDoclist;                               /* Doclist data */
+
+  if( nData>0 && nData+nReq>p->nNodeSize ){
+    int rc;
+
+    /* The current leaf node is full. Write it out to the database. */
+    rc = fts3WriteSegment(p, pWriter->iFree++, pWriter->aData, nData);
+    if( rc!=SQLITE_OK ) return rc;
+    p->nLeafAdd++;
+
+    /* Add the current term to the interior node tree. The term added to
+    ** the interior tree must:
+    **
+    **   a) be greater than the largest term on the leaf node just written
+    **      to the database (still available in pWriter->zTerm), and
+    **
+    **   b) be less than or equal to the term about to be added to the new
+    **      leaf node (zTerm/nTerm).
+    **
+    ** In other words, it must be the prefix of zTerm 1 byte longer than
+    ** the common prefix (if any) of zTerm and pWriter->zTerm.
+    */
+    assert( nPrefix<nTerm );
+    rc = fts3NodeAddTerm(p, &pWriter->pTree, isCopyTerm, zTerm, nPrefix+1);
+    if( rc!=SQLITE_OK ) return rc;
+
+    nData = 0;
+    pWriter->nTerm = 0;
+
+    nPrefix = 0;
+    nSuffix = nTerm;
+    nReq = 1 +                              /* varint containing prefix size */
+      sqlite3Fts3VarintLen(nTerm) +         /* varint containing suffix size */
+      nTerm +                               /* Term suffix */
+      sqlite3Fts3VarintLen(nDoclist) +      /* Size of doclist */
+      nDoclist;                             /* Doclist data */
+  }
+
+  /* Increase the total number of bytes written to account for the new entry. */
+  pWriter->nLeafData += nReq;
+
+  /* If the buffer currently allocated is too small for this entry, realloc
+  ** the buffer to make it large enough.
+  */
+  if( nReq>pWriter->nSize ){
+    char *aNew = sqlite3_realloc(pWriter->aData, nReq);
+    if( !aNew ) return SQLITE_NOMEM;
+    pWriter->aData = aNew;
+    pWriter->nSize = nReq;
+  }
+  assert( nData+nReq<=pWriter->nSize );
+
+  /* Append the prefix-compressed term and doclist to the buffer. */
+  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nPrefix);
+  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nSuffix);
+  memcpy(&pWriter->aData[nData], &zTerm[nPrefix], nSuffix);
+  nData += nSuffix;
+  nData += sqlite3Fts3PutVarint(&pWriter->aData[nData], nDoclist);
+  memcpy(&pWriter->aData[nData], aDoclist, nDoclist);
+  pWriter->nData = nData + nDoclist;
+
+  /* Save the current term so that it can be used to prefix-compress the next.
+  ** If the isCopyTerm parameter is true, then the buffer pointed to by
+  ** zTerm is transient, so take a copy of the term data. Otherwise, just
+  ** store a copy of the pointer.
+  */
+  if( isCopyTerm ){
+    if( nTerm>pWriter->nMalloc ){
+      char *zNew = sqlite3_realloc(pWriter->zMalloc, nTerm*2);
+      if( !zNew ){
+        return SQLITE_NOMEM;
+      }
+      pWriter->nMalloc = nTerm*2;
+      pWriter->zMalloc = zNew;
+      pWriter->zTerm = zNew;
+    }
+    assert( pWriter->zTerm==pWriter->zMalloc );
+    memcpy(pWriter->zTerm, zTerm, nTerm);
+  }else{
+    pWriter->zTerm = (char *)zTerm;
+  }
+  pWriter->nTerm = nTerm;
+
+  return SQLITE_OK;
+}
+
+/*
+** Flush all data associated with the SegmentWriter object pWriter to the
+** database. This function must be called after all terms have been added
+** to the segment using fts3SegWriterAdd(). If successful, SQLITE_OK is
+** returned. Otherwise, an SQLite error code.
+*/
+static int fts3SegWriterFlush(
+  Fts3Table *p,                   /* Virtual table handle */
+  SegmentWriter *pWriter,         /* SegmentWriter to flush to the db */
+  sqlite3_int64 iLevel,           /* Value for 'level' column of %_segdir */
+  int iIdx                        /* Value for 'idx' column of %_segdir */
+){
+  int rc;                         /* Return code */
+  if( pWriter->pTree ){
+    sqlite3_int64 iLast = 0;      /* Largest block id written to database */
+    sqlite3_int64 iLastLeaf;      /* Largest leaf block id written to db */
+    char *zRoot = NULL;           /* Pointer to buffer containing root node */
+    int nRoot = 0;                /* Size of buffer zRoot */
+
+    iLastLeaf = pWriter->iFree;
+    rc = fts3WriteSegment(p, pWriter->iFree++, pWriter->aData, pWriter->nData);
+    if( rc==SQLITE_OK ){
+      rc = fts3NodeWrite(p, pWriter->pTree, 1,
+          pWriter->iFirst, pWriter->iFree, &iLast, &zRoot, &nRoot);
+    }
+    if( rc==SQLITE_OK ){
+      rc = fts3WriteSegdir(p, iLevel, iIdx, 
+          pWriter->iFirst, iLastLeaf, iLast, pWriter->nLeafData, zRoot, nRoot);
+    }
+  }else{
+    /* The entire tree fits on the root node. Write it to the segdir table. */
+    rc = fts3WriteSegdir(p, iLevel, iIdx, 
+        0, 0, 0, pWriter->nLeafData, pWriter->aData, pWriter->nData);
+  }
+  p->nLeafAdd++;
+  return rc;
+}
+
+/*
+** Release all memory held by the SegmentWriter object passed as the 
+** first argument.
+*/
+static void fts3SegWriterFree(SegmentWriter *pWriter){
+  if( pWriter ){
+    sqlite3_free(pWriter->aData);
+    sqlite3_free(pWriter->zMalloc);
+    fts3NodeFree(pWriter->pTree);
+    sqlite3_free(pWriter);
+  }
+}
+
+/*
+** The first value in the apVal[] array is assumed to contain an integer.
+** This function tests if there exist any documents with docid values that
+** are different from that integer. i.e. if deleting the document with docid
+** pRowid would mean the FTS3 table were empty.
+**
+** If successful, *pisEmpty is set to true if the table is empty except for
+** document pRowid, or false otherwise, and SQLITE_OK is returned. If an
+** error occurs, an SQLite error code is returned.
+*/
+static int fts3IsEmpty(Fts3Table *p, sqlite3_value *pRowid, int *pisEmpty){
+  sqlite3_stmt *pStmt;
+  int rc;
+  if( p->zContentTbl ){
+    /* If using the content=xxx option, assume the table is never empty */
+    *pisEmpty = 0;
+    rc = SQLITE_OK;
+  }else{
+    rc = fts3SqlStmt(p, SQL_IS_EMPTY, &pStmt, &pRowid);
+    if( rc==SQLITE_OK ){
+      if( SQLITE_ROW==sqlite3_step(pStmt) ){
+        *pisEmpty = sqlite3_column_int(pStmt, 0);
+      }
+      rc = sqlite3_reset(pStmt);
+    }
+  }
+  return rc;
+}
+
+/*
+** Set *pnMax to the largest segment level in the database for the index
+** iIndex.
+**
+** Segment levels are stored in the 'level' column of the %_segdir table.
+**
+** Return SQLITE_OK if successful, or an SQLite error code if not.
+*/
+static int fts3SegmentMaxLevel(
+  Fts3Table *p, 
+  int iLangid,
+  int iIndex, 
+  sqlite3_int64 *pnMax
+){
+  sqlite3_stmt *pStmt;
+  int rc;
+  assert( iIndex>=0 && iIndex<p->nIndex );
+
+  /* Set pStmt to the compiled version of:
+  **
+  **   SELECT max(level) FROM %Q.'%q_segdir' WHERE level BETWEEN ? AND ?
+  **
+  ** (1024 is actually the value of macro FTS3_SEGDIR_PREFIXLEVEL_STR).
+  */
+  rc = fts3SqlStmt(p, SQL_SELECT_SEGDIR_MAX_LEVEL, &pStmt, 0);
+  if( rc!=SQLITE_OK ) return rc;
+  sqlite3_bind_int64(pStmt, 1, getAbsoluteLevel(p, iLangid, iIndex, 0));
+  sqlite3_bind_int64(pStmt, 2, 
+      getAbsoluteLevel(p, iLangid, iIndex, FTS3_SEGDIR_MAXLEVEL-1)
+  );
+  if( SQLITE_ROW==sqlite3_step(pStmt) ){
+    *pnMax = sqlite3_column_int64(pStmt, 0);
+  }
+  return sqlite3_reset(pStmt);
+}
+
+/*
+** iAbsLevel is an absolute level that may be assumed to exist within
+** the database. This function checks if it is the largest level number
+** within its index. Assuming no error occurs, *pbMax is set to 1 if
+** iAbsLevel is indeed the largest level, or 0 otherwise, and SQLITE_OK
+** is returned. If an error occurs, an error code is returned and the
+** final value of *pbMax is undefined.
+*/
+static int fts3SegmentIsMaxLevel(Fts3Table *p, i64 iAbsLevel, int *pbMax){
+
+  /* Set pStmt to the compiled version of:
+  **
+  **   SELECT max(level) FROM %Q.'%q_segdir' WHERE level BETWEEN ? AND ?
+  **
+  ** (1024 is actually the value of macro FTS3_SEGDIR_PREFIXLEVEL_STR).
+  */
+  sqlite3_stmt *pStmt;
+  int rc = fts3SqlStmt(p, SQL_SELECT_SEGDIR_MAX_LEVEL, &pStmt, 0);
+  if( rc!=SQLITE_OK ) return rc;
+  sqlite3_bind_int64(pStmt, 1, iAbsLevel+1);
+  sqlite3_bind_int64(pStmt, 2, 
+      ((iAbsLevel/FTS3_SEGDIR_MAXLEVEL)+1) * FTS3_SEGDIR_MAXLEVEL
+  );
+
+  *pbMax = 0;
+  if( SQLITE_ROW==sqlite3_step(pStmt) ){
+    *pbMax = sqlite3_column_type(pStmt, 0)==SQLITE_NULL;
+  }
+  return sqlite3_reset(pStmt);
+}
+
+/*
+** Delete all entries in the %_segments table associated with the segment
+** opened with seg-reader pSeg. This function does not affect the contents
+** of the %_segdir table.
+*/
+static int fts3DeleteSegment(
+  Fts3Table *p,                   /* FTS table handle */
+  Fts3SegReader *pSeg             /* Segment to delete */
+){
+  int rc = SQLITE_OK;             /* Return code */
+  if( pSeg->iStartBlock ){
+    sqlite3_stmt *pDelete;        /* SQL statement to delete rows */
+    rc = fts3SqlStmt(p, SQL_DELETE_SEGMENTS_RANGE, &pDelete, 0);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_int64(pDelete, 1, pSeg->iStartBlock);
+      sqlite3_bind_int64(pDelete, 2, pSeg->iEndBlock);
+      sqlite3_step(pDelete);
+      rc = sqlite3_reset(pDelete);
+    }
+  }
+  return rc;
+}
+
+/*
+** This function is used after merging multiple segments into a single large
+** segment to delete the old, now redundant, segment b-trees. Specifically,
+** it:
+** 
+**   1) Deletes all %_segments entries for the segments associated with 
+**      each of the SegReader objects in the array passed as the third 
+**      argument, and
+**
+**   2) deletes all %_segdir entries with level iLevel, or all %_segdir
+**      entries regardless of level if (iLevel<0).
+**
+** SQLITE_OK is returned if successful, otherwise an SQLite error code.
+*/
+static int fts3DeleteSegdir(
+  Fts3Table *p,                   /* Virtual table handle */
+  int iLangid,                    /* Language id */
+  int iIndex,                     /* Index for p->aIndex */
+  int iLevel,                     /* Level of %_segdir entries to delete */
+  Fts3SegReader **apSegment,      /* Array of SegReader objects */
+  int nReader                     /* Size of array apSegment */
+){
+  int rc = SQLITE_OK;             /* Return Code */
+  int i;                          /* Iterator variable */
+  sqlite3_stmt *pDelete = 0;      /* SQL statement to delete rows */
+
+  for(i=0; rc==SQLITE_OK && i<nReader; i++){
+    rc = fts3DeleteSegment(p, apSegment[i]);
+  }
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+
+  assert( iLevel>=0 || iLevel==FTS3_SEGCURSOR_ALL );
+  if( iLevel==FTS3_SEGCURSOR_ALL ){
+    rc = fts3SqlStmt(p, SQL_DELETE_SEGDIR_RANGE, &pDelete, 0);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_int64(pDelete, 1, getAbsoluteLevel(p, iLangid, iIndex, 0));
+      sqlite3_bind_int64(pDelete, 2, 
+          getAbsoluteLevel(p, iLangid, iIndex, FTS3_SEGDIR_MAXLEVEL-1)
+      );
+    }
+  }else{
+    rc = fts3SqlStmt(p, SQL_DELETE_SEGDIR_LEVEL, &pDelete, 0);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_int64(
+          pDelete, 1, getAbsoluteLevel(p, iLangid, iIndex, iLevel)
+      );
+    }
+  }
+
+  if( rc==SQLITE_OK ){
+    sqlite3_step(pDelete);
+    rc = sqlite3_reset(pDelete);
+  }
+
+  return rc;
+}
+
+/*
+** When this function is called, buffer *ppList (size *pnList bytes) contains 
+** a position list that may (or may not) feature multiple columns. This
+** function adjusts the pointer *ppList and the length *pnList so that they
+** identify the subset of the position list that corresponds to column iCol.
+**
+** If there are no entries in the input position list for column iCol, then
+** *pnList is set to zero before returning.
+**
+** If parameter bZero is non-zero, then any part of the input list following
+** the end of the output list is zeroed before returning.
+*/
+static void fts3ColumnFilter(
+  int iCol,                       /* Column to filter on */
+  int bZero,                      /* Zero out anything following *ppList */
+  char **ppList,                  /* IN/OUT: Pointer to position list */
+  int *pnList                     /* IN/OUT: Size of buffer *ppList in bytes */
+){
+  char *pList = *ppList;
+  int nList = *pnList;
+  char *pEnd = &pList[nList];
+  int iCurrent = 0;
+  char *p = pList;
+
+  assert( iCol>=0 );
+  while( 1 ){
+    char c = 0;
+    while( p<pEnd && (c | *p)&0xFE ) c = *p++ & 0x80;
+  
+    if( iCol==iCurrent ){
+      nList = (int)(p - pList);
+      break;
+    }
+
+    nList -= (int)(p - pList);
+    pList = p;
+    if( nList==0 ){
+      break;
+    }
+    p = &pList[1];
+    p += fts3GetVarint32(p, &iCurrent);
+  }
+
+  if( bZero && &pList[nList]!=pEnd ){
+    memset(&pList[nList], 0, pEnd - &pList[nList]);
+  }
+  *ppList = pList;
+  *pnList = nList;
+}
+
+/*
+** Cache data in the Fts3MultiSegReader.aBuffer[] buffer (overwriting any
+** existing data). Grow the buffer if required.
+**
+** If successful, return SQLITE_OK. Otherwise, if an OOM error is encountered
+** trying to resize the buffer, return SQLITE_NOMEM.
+*/
+static int fts3MsrBufferData(
+  Fts3MultiSegReader *pMsr,       /* Multi-segment-reader handle */
+  char *pList,
+  int nList
+){
+  if( nList>pMsr->nBuffer ){
+    char *pNew;
+    pMsr->nBuffer = nList*2;
+    pNew = (char *)sqlite3_realloc(pMsr->aBuffer, pMsr->nBuffer);
+    if( !pNew ) return SQLITE_NOMEM;
+    pMsr->aBuffer = pNew;
+  }
+
+  memcpy(pMsr->aBuffer, pList, nList);
+  return SQLITE_OK;
+}
+
+int sqlite3Fts3MsrIncrNext(
+  Fts3Table *p,                   /* Virtual table handle */
+  Fts3MultiSegReader *pMsr,       /* Multi-segment-reader handle */
+  sqlite3_int64 *piDocid,         /* OUT: Docid value */
+  char **paPoslist,               /* OUT: Pointer to position list */
+  int *pnPoslist                  /* OUT: Size of position list in bytes */
+){
+  int nMerge = pMsr->nAdvance;
+  Fts3SegReader **apSegment = pMsr->apSegment;
+  int (*xCmp)(Fts3SegReader *, Fts3SegReader *) = (
+    p->bDescIdx ? fts3SegReaderDoclistCmpRev : fts3SegReaderDoclistCmp
+  );
+
+  if( nMerge==0 ){
+    *paPoslist = 0;
+    return SQLITE_OK;
+  }
+
+  while( 1 ){
+    Fts3SegReader *pSeg;
+    pSeg = pMsr->apSegment[0];
+
+    if( pSeg->pOffsetList==0 ){
+      *paPoslist = 0;
+      break;
+    }else{
+      int rc;
+      char *pList;
+      int nList;
+      int j;
+      sqlite3_int64 iDocid = apSegment[0]->iDocid;
+
+      rc = fts3SegReaderNextDocid(p, apSegment[0], &pList, &nList);
+      j = 1;
+      while( rc==SQLITE_OK 
+        && j<nMerge
+        && apSegment[j]->pOffsetList
+        && apSegment[j]->iDocid==iDocid
+      ){
+        rc = fts3SegReaderNextDocid(p, apSegment[j], 0, 0);
+        j++;
+      }
+      if( rc!=SQLITE_OK ) return rc;
+      fts3SegReaderSort(pMsr->apSegment, nMerge, j, xCmp);
+
+      if( nList>0 && fts3SegReaderIsPending(apSegment[0]) ){
+        rc = fts3MsrBufferData(pMsr, pList, nList+1);
+        if( rc!=SQLITE_OK ) return rc;
+        assert( (pMsr->aBuffer[nList] & 0xFE)==0x00 );
+        pList = pMsr->aBuffer;
+      }
+
+      if( pMsr->iColFilter>=0 ){
+        fts3ColumnFilter(pMsr->iColFilter, 1, &pList, &nList);
+      }
+
+      if( nList>0 ){
+        *paPoslist = pList;
+        *piDocid = iDocid;
+        *pnPoslist = nList;
+        break;
+      }
+    }
+  }
+
+  return SQLITE_OK;
+}
+
+static int fts3SegReaderStart(
+  Fts3Table *p,                   /* Virtual table handle */
+  Fts3MultiSegReader *pCsr,       /* Cursor object */
+  const char *zTerm,              /* Term searched for (or NULL) */
+  int nTerm                       /* Length of zTerm in bytes */
+){
+  int i;
+  int nSeg = pCsr->nSegment;
+
+  /* If the Fts3SegFilter defines a specific term (or term prefix) to search 
+  ** for, then advance each segment iterator until it points to a term of
+  ** equal or greater value than the specified term. This prevents many
+  ** unnecessary merge/sort operations for the case where single segment
+  ** b-tree leaf nodes contain more than one term.
+  */
+  for(i=0; pCsr->bRestart==0 && i<pCsr->nSegment; i++){
+    int res = 0;
+    Fts3SegReader *pSeg = pCsr->apSegment[i];
+    do {
+      int rc = fts3SegReaderNext(p, pSeg, 0);
+      if( rc!=SQLITE_OK ) return rc;
+    }while( zTerm && (res = fts3SegReaderTermCmp(pSeg, zTerm, nTerm))<0 );
+
+    if( pSeg->bLookup && res!=0 ){
+      fts3SegReaderSetEof(pSeg);
+    }
+  }
+  fts3SegReaderSort(pCsr->apSegment, nSeg, nSeg, fts3SegReaderCmp);
+
+  return SQLITE_OK;
+}
+
+int sqlite3Fts3SegReaderStart(
+  Fts3Table *p,                   /* Virtual table handle */
+  Fts3MultiSegReader *pCsr,       /* Cursor object */
+  Fts3SegFilter *pFilter          /* Restrictions on range of iteration */
+){
+  pCsr->pFilter = pFilter;
+  return fts3SegReaderStart(p, pCsr, pFilter->zTerm, pFilter->nTerm);
+}
+
+int sqlite3Fts3MsrIncrStart(
+  Fts3Table *p,                   /* Virtual table handle */
+  Fts3MultiSegReader *pCsr,       /* Cursor object */
+  int iCol,                       /* Column to match on. */
+  const char *zTerm,              /* Term to iterate through a doclist for */
+  int nTerm                       /* Number of bytes in zTerm */
+){
+  int i;
+  int rc;
+  int nSegment = pCsr->nSegment;
+  int (*xCmp)(Fts3SegReader *, Fts3SegReader *) = (
+    p->bDescIdx ? fts3SegReaderDoclistCmpRev : fts3SegReaderDoclistCmp
+  );
+
+  assert( pCsr->pFilter==0 );
+  assert( zTerm && nTerm>0 );
+
+  /* Advance each segment iterator until it points to the term zTerm/nTerm. */
+  rc = fts3SegReaderStart(p, pCsr, zTerm, nTerm);
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* Determine how many of the segments actually point to zTerm/nTerm. */
+  for(i=0; i<nSegment; i++){
+    Fts3SegReader *pSeg = pCsr->apSegment[i];
+    if( !pSeg->aNode || fts3SegReaderTermCmp(pSeg, zTerm, nTerm) ){
+      break;
+    }
+  }
+  pCsr->nAdvance = i;
+
+  /* Advance each of the segments to point to the first docid. */
+  for(i=0; i<pCsr->nAdvance; i++){
+    rc = fts3SegReaderFirstDocid(p, pCsr->apSegment[i]);
+    if( rc!=SQLITE_OK ) return rc;
+  }
+  fts3SegReaderSort(pCsr->apSegment, i, i, xCmp);
+
+  assert( iCol<0 || iCol<p->nColumn );
+  pCsr->iColFilter = iCol;
+
+  return SQLITE_OK;
+}
+
+/*
+** This function is called on a MultiSegReader that has been started using
+** sqlite3Fts3MsrIncrStart(). One or more calls to MsrIncrNext() may also
+** have been made. Calling this function puts the MultiSegReader in such
+** a state that if the next two calls are:
+**
+**   sqlite3Fts3SegReaderStart()
+**   sqlite3Fts3SegReaderStep()
+**
+** then the entire doclist for the term is available in 
+** MultiSegReader.aDoclist/nDoclist.
+*/
+int sqlite3Fts3MsrIncrRestart(Fts3MultiSegReader *pCsr){
+  int i;                          /* Used to iterate through segment-readers */
+
+  assert( pCsr->zTerm==0 );
+  assert( pCsr->nTerm==0 );
+  assert( pCsr->aDoclist==0 );
+  assert( pCsr->nDoclist==0 );
+
+  pCsr->nAdvance = 0;
+  pCsr->bRestart = 1;
+  for(i=0; i<pCsr->nSegment; i++){
+    pCsr->apSegment[i]->pOffsetList = 0;
+    pCsr->apSegment[i]->nOffsetList = 0;
+    pCsr->apSegment[i]->iDocid = 0;
+  }
+
+  return SQLITE_OK;
+}
+
+
+int sqlite3Fts3SegReaderStep(
+  Fts3Table *p,                   /* Virtual table handle */
+  Fts3MultiSegReader *pCsr        /* Cursor object */
+){
+  int rc = SQLITE_OK;
+
+  int isIgnoreEmpty =  (pCsr->pFilter->flags & FTS3_SEGMENT_IGNORE_EMPTY);
+  int isRequirePos =   (pCsr->pFilter->flags & FTS3_SEGMENT_REQUIRE_POS);
+  int isColFilter =    (pCsr->pFilter->flags & FTS3_SEGMENT_COLUMN_FILTER);
+  int isPrefix =       (pCsr->pFilter->flags & FTS3_SEGMENT_PREFIX);
+  int isScan =         (pCsr->pFilter->flags & FTS3_SEGMENT_SCAN);
+  int isFirst =        (pCsr->pFilter->flags & FTS3_SEGMENT_FIRST);
+
+  Fts3SegReader **apSegment = pCsr->apSegment;
+  int nSegment = pCsr->nSegment;
+  Fts3SegFilter *pFilter = pCsr->pFilter;
+  int (*xCmp)(Fts3SegReader *, Fts3SegReader *) = (
+    p->bDescIdx ? fts3SegReaderDoclistCmpRev : fts3SegReaderDoclistCmp
+  );
+
+  if( pCsr->nSegment==0 ) return SQLITE_OK;
+
+  do {
+    int nMerge;
+    int i;
+  
+    /* Advance the first pCsr->nAdvance entries in the apSegment[] array
+    ** forward. Then sort the list in order of current term again.  
+    */
+    for(i=0; i<pCsr->nAdvance; i++){
+      Fts3SegReader *pSeg = apSegment[i];
+      if( pSeg->bLookup ){
+        fts3SegReaderSetEof(pSeg);
+      }else{
+        rc = fts3SegReaderNext(p, pSeg, 0);
+      }
+      if( rc!=SQLITE_OK ) return rc;
+    }
+    fts3SegReaderSort(apSegment, nSegment, pCsr->nAdvance, fts3SegReaderCmp);
+    pCsr->nAdvance = 0;
+
+    /* If all the seg-readers are at EOF, we're finished. return SQLITE_OK. */
+    assert( rc==SQLITE_OK );
+    if( apSegment[0]->aNode==0 ) break;
+
+    pCsr->nTerm = apSegment[0]->nTerm;
+    pCsr->zTerm = apSegment[0]->zTerm;
+
+    /* If this is a prefix-search, and if the term that apSegment[0] points
+    ** to does not share a suffix with pFilter->zTerm/nTerm, then all 
+    ** required callbacks have been made. In this case exit early.
+    **
+    ** Similarly, if this is a search for an exact match, and the first term
+    ** of segment apSegment[0] is not a match, exit early.
+    */
+    if( pFilter->zTerm && !isScan ){
+      if( pCsr->nTerm<pFilter->nTerm 
+       || (!isPrefix && pCsr->nTerm>pFilter->nTerm)
+       || memcmp(pCsr->zTerm, pFilter->zTerm, pFilter->nTerm) 
+      ){
+        break;
+      }
+    }
+
+    nMerge = 1;
+    while( nMerge<nSegment 
+        && apSegment[nMerge]->aNode
+        && apSegment[nMerge]->nTerm==pCsr->nTerm 
+        && 0==memcmp(pCsr->zTerm, apSegment[nMerge]->zTerm, pCsr->nTerm)
+    ){
+      nMerge++;
+    }
+
+    assert( isIgnoreEmpty || (isRequirePos && !isColFilter) );
+    if( nMerge==1 
+     && !isIgnoreEmpty 
+     && !isFirst 
+     && (p->bDescIdx==0 || fts3SegReaderIsPending(apSegment[0])==0)
+    ){
+      pCsr->nDoclist = apSegment[0]->nDoclist;
+      if( fts3SegReaderIsPending(apSegment[0]) ){
+        rc = fts3MsrBufferData(pCsr, apSegment[0]->aDoclist, pCsr->nDoclist);
+        pCsr->aDoclist = pCsr->aBuffer;
+      }else{
+        pCsr->aDoclist = apSegment[0]->aDoclist;
+      }
+      if( rc==SQLITE_OK ) rc = SQLITE_ROW;
+    }else{
+      int nDoclist = 0;           /* Size of doclist */
+      sqlite3_int64 iPrev = 0;    /* Previous docid stored in doclist */
+
+      /* The current term of the first nMerge entries in the array
+      ** of Fts3SegReader objects is the same. The doclists must be merged
+      ** and a single term returned with the merged doclist.
+      */
+      for(i=0; i<nMerge; i++){
+        fts3SegReaderFirstDocid(p, apSegment[i]);
+      }
+      fts3SegReaderSort(apSegment, nMerge, nMerge, xCmp);
+      while( apSegment[0]->pOffsetList ){
+        int j;                    /* Number of segments that share a docid */
+        char *pList = 0;
+        int nList = 0;
+        int nByte;
+        sqlite3_int64 iDocid = apSegment[0]->iDocid;
+        fts3SegReaderNextDocid(p, apSegment[0], &pList, &nList);
+        j = 1;
+        while( j<nMerge
+            && apSegment[j]->pOffsetList
+            && apSegment[j]->iDocid==iDocid
+        ){
+          fts3SegReaderNextDocid(p, apSegment[j], 0, 0);
+          j++;
+        }
+
+        if( isColFilter ){
+          fts3ColumnFilter(pFilter->iCol, 0, &pList, &nList);
+        }
+
+        if( !isIgnoreEmpty || nList>0 ){
+
+          /* Calculate the 'docid' delta value to write into the merged 
+          ** doclist. */
+          sqlite3_int64 iDelta;
+          if( p->bDescIdx && nDoclist>0 ){
+            iDelta = iPrev - iDocid;
+          }else{
+            iDelta = iDocid - iPrev;
+          }
+          assert( iDelta>0 || (nDoclist==0 && iDelta==iDocid) );
+          assert( nDoclist>0 || iDelta==iDocid );
+
+          nByte = sqlite3Fts3VarintLen(iDelta) + (isRequirePos?nList+1:0);
+          if( nDoclist+nByte>pCsr->nBuffer ){
+            char *aNew;
+            pCsr->nBuffer = (nDoclist+nByte)*2;
+            aNew = sqlite3_realloc(pCsr->aBuffer, pCsr->nBuffer);
+            if( !aNew ){
+              return SQLITE_NOMEM;
+            }
+            pCsr->aBuffer = aNew;
+          }
+
+          if( isFirst ){
+            char *a = &pCsr->aBuffer[nDoclist];
+            int nWrite;
+           
+            nWrite = sqlite3Fts3FirstFilter(iDelta, pList, nList, a);
+            if( nWrite ){
+              iPrev = iDocid;
+              nDoclist += nWrite;
+            }
+          }else{
+            nDoclist += sqlite3Fts3PutVarint(&pCsr->aBuffer[nDoclist], iDelta);
+            iPrev = iDocid;
+            if( isRequirePos ){
+              memcpy(&pCsr->aBuffer[nDoclist], pList, nList);
+              nDoclist += nList;
+              pCsr->aBuffer[nDoclist++] = '\0';
+            }
+          }
+        }
+
+        fts3SegReaderSort(apSegment, nMerge, j, xCmp);
+      }
+      if( nDoclist>0 ){
+        pCsr->aDoclist = pCsr->aBuffer;
+        pCsr->nDoclist = nDoclist;
+        rc = SQLITE_ROW;
+      }
+    }
+    pCsr->nAdvance = nMerge;
+  }while( rc==SQLITE_OK );
+
+  return rc;
+}
+
+
+void sqlite3Fts3SegReaderFinish(
+  Fts3MultiSegReader *pCsr       /* Cursor object */
+){
+  if( pCsr ){
+    int i;
+    for(i=0; i<pCsr->nSegment; i++){
+      sqlite3Fts3SegReaderFree(pCsr->apSegment[i]);
+    }
+    sqlite3_free(pCsr->apSegment);
+    sqlite3_free(pCsr->aBuffer);
+
+    pCsr->nSegment = 0;
+    pCsr->apSegment = 0;
+    pCsr->aBuffer = 0;
+  }
+}
+
+/*
+** Decode the "end_block" field, selected by column iCol of the SELECT 
+** statement passed as the first argument. 
+**
+** The "end_block" field may contain either an integer, or a text field
+** containing the text representation of two non-negative integers separated 
+** by one or more space (0x20) characters. In the first case, set *piEndBlock 
+** to the integer value and *pnByte to zero before returning. In the second, 
+** set *piEndBlock to the first value and *pnByte to the second.
+*/
+static void fts3ReadEndBlockField(
+  sqlite3_stmt *pStmt, 
+  int iCol, 
+  i64 *piEndBlock,
+  i64 *pnByte
+){
+  const unsigned char *zText = sqlite3_column_text(pStmt, iCol);
+  if( zText ){
+    int i;
+    int iMul = 1;
+    i64 iVal = 0;
+    for(i=0; zText[i]>='0' && zText[i]<='9'; i++){
+      iVal = iVal*10 + (zText[i] - '0');
+    }
+    *piEndBlock = iVal;
+    while( zText[i]==' ' ) i++;
+    iVal = 0;
+    if( zText[i]=='-' ){
+      i++;
+      iMul = -1;
+    }
+    for(/* no-op */; zText[i]>='0' && zText[i]<='9'; i++){
+      iVal = iVal*10 + (zText[i] - '0');
+    }
+    *pnByte = (iVal * (i64)iMul);
+  }
+}
+
+
+/*
+** A segment of size nByte bytes has just been written to absolute level
+** iAbsLevel. Promote any segments that should be promoted as a result.
+*/
+static int fts3PromoteSegments(
+  Fts3Table *p,                   /* FTS table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute level just updated */
+  sqlite3_int64 nByte             /* Size of new segment at iAbsLevel */
+){
+  int rc = SQLITE_OK;
+  sqlite3_stmt *pRange;
+
+  rc = fts3SqlStmt(p, SQL_SELECT_LEVEL_RANGE2, &pRange, 0);
+
+  if( rc==SQLITE_OK ){
+    int bOk = 0;
+    i64 iLast = (iAbsLevel/FTS3_SEGDIR_MAXLEVEL + 1) * FTS3_SEGDIR_MAXLEVEL - 1;
+    i64 nLimit = (nByte*3)/2;
+
+    /* Loop through all entries in the %_segdir table corresponding to 
+    ** segments in this index on levels greater than iAbsLevel. If there is
+    ** at least one such segment, and it is possible to determine that all 
+    ** such segments are smaller than nLimit bytes in size, they will be 
+    ** promoted to level iAbsLevel.  */
+    sqlite3_bind_int64(pRange, 1, iAbsLevel+1);
+    sqlite3_bind_int64(pRange, 2, iLast);
+    while( SQLITE_ROW==sqlite3_step(pRange) ){
+      i64 nSize = 0, dummy;
+      fts3ReadEndBlockField(pRange, 2, &dummy, &nSize);
+      if( nSize<=0 || nSize>nLimit ){
+        /* If nSize==0, then the %_segdir.end_block field does not not 
+        ** contain a size value. This happens if it was written by an
+        ** old version of FTS. In this case it is not possible to determine
+        ** the size of the segment, and so segment promotion does not
+        ** take place.  */
+        bOk = 0;
+        break;
+      }
+      bOk = 1;
+    }
+    rc = sqlite3_reset(pRange);
+
+    if( bOk ){
+      int iIdx = 0;
+      sqlite3_stmt *pUpdate1 = 0;
+      sqlite3_stmt *pUpdate2 = 0;
+
+      if( rc==SQLITE_OK ){
+        rc = fts3SqlStmt(p, SQL_UPDATE_LEVEL_IDX, &pUpdate1, 0);
+      }
+      if( rc==SQLITE_OK ){
+        rc = fts3SqlStmt(p, SQL_UPDATE_LEVEL, &pUpdate2, 0);
+      }
+
+      if( rc==SQLITE_OK ){
+
+        /* Loop through all %_segdir entries for segments in this index with
+        ** levels equal to or greater than iAbsLevel. As each entry is visited,
+        ** updated it to set (level = -1) and (idx = N), where N is 0 for the
+        ** oldest segment in the range, 1 for the next oldest, and so on.
+        **
+        ** In other words, move all segments being promoted to level -1,
+        ** setting the "idx" fields as appropriate to keep them in the same
+        ** order. The contents of level -1 (which is never used, except
+        ** transiently here), will be moved back to level iAbsLevel below.  */
+        sqlite3_bind_int64(pRange, 1, iAbsLevel);
+        while( SQLITE_ROW==sqlite3_step(pRange) ){
+          sqlite3_bind_int(pUpdate1, 1, iIdx++);
+          sqlite3_bind_int(pUpdate1, 2, sqlite3_column_int(pRange, 0));
+          sqlite3_bind_int(pUpdate1, 3, sqlite3_column_int(pRange, 1));
+          sqlite3_step(pUpdate1);
+          rc = sqlite3_reset(pUpdate1);
+          if( rc!=SQLITE_OK ){
+            sqlite3_reset(pRange);
+            break;
+          }
+        }
+      }
+      if( rc==SQLITE_OK ){
+        rc = sqlite3_reset(pRange);
+      }
+
+      /* Move level -1 to level iAbsLevel */
+      if( rc==SQLITE_OK ){
+        sqlite3_bind_int64(pUpdate2, 1, iAbsLevel);
+        sqlite3_step(pUpdate2);
+        rc = sqlite3_reset(pUpdate2);
+      }
+    }
+  }
+
+
+  return rc;
+}
+
+/*
+** Merge all level iLevel segments in the database into a single 
+** iLevel+1 segment. Or, if iLevel<0, merge all segments into a
+** single segment with a level equal to the numerically largest level 
+** currently present in the database.
+**
+** If this function is called with iLevel<0, but there is only one
+** segment in the database, SQLITE_DONE is returned immediately. 
+** Otherwise, if successful, SQLITE_OK is returned. If an error occurs, 
+** an SQLite error code is returned.
+*/
+static int fts3SegmentMerge(
+  Fts3Table *p, 
+  int iLangid,                    /* Language id to merge */
+  int iIndex,                     /* Index in p->aIndex[] to merge */
+  int iLevel                      /* Level to merge */
+){
+  int rc;                         /* Return code */
+  int iIdx = 0;                   /* Index of new segment */
+  sqlite3_int64 iNewLevel = 0;    /* Level/index to create new segment at */
+  SegmentWriter *pWriter = 0;     /* Used to write the new, merged, segment */
+  Fts3SegFilter filter;           /* Segment term filter condition */
+  Fts3MultiSegReader csr;         /* Cursor to iterate through level(s) */
+  int bIgnoreEmpty = 0;           /* True to ignore empty segments */
+  i64 iMaxLevel = 0;              /* Max level number for this index/langid */
+
+  assert( iLevel==FTS3_SEGCURSOR_ALL
+       || iLevel==FTS3_SEGCURSOR_PENDING
+       || iLevel>=0
+  );
+  assert( iLevel<FTS3_SEGDIR_MAXLEVEL );
+  assert( iIndex>=0 && iIndex<p->nIndex );
+
+  rc = sqlite3Fts3SegReaderCursor(p, iLangid, iIndex, iLevel, 0, 0, 1, 0, &csr);
+  if( rc!=SQLITE_OK || csr.nSegment==0 ) goto finished;
+
+  if( iLevel!=FTS3_SEGCURSOR_PENDING ){
+    rc = fts3SegmentMaxLevel(p, iLangid, iIndex, &iMaxLevel);
+    if( rc!=SQLITE_OK ) goto finished;
+  }
+
+  if( iLevel==FTS3_SEGCURSOR_ALL ){
+    /* This call is to merge all segments in the database to a single
+    ** segment. The level of the new segment is equal to the numerically
+    ** greatest segment level currently present in the database for this
+    ** index. The idx of the new segment is always 0.  */
+    if( csr.nSegment==1 && 0==fts3SegReaderIsPending(csr.apSegment[0]) ){
+      rc = SQLITE_DONE;
+      goto finished;
+    }
+    iNewLevel = iMaxLevel;
+    bIgnoreEmpty = 1;
+
+  }else{
+    /* This call is to merge all segments at level iLevel. find the next
+    ** available segment index at level iLevel+1. The call to
+    ** fts3AllocateSegdirIdx() will merge the segments at level iLevel+1 to 
+    ** a single iLevel+2 segment if necessary.  */
+    assert( FTS3_SEGCURSOR_PENDING==-1 );
+    iNewLevel = getAbsoluteLevel(p, iLangid, iIndex, iLevel+1);
+    rc = fts3AllocateSegdirIdx(p, iLangid, iIndex, iLevel+1, &iIdx);
+    bIgnoreEmpty = (iLevel!=FTS3_SEGCURSOR_PENDING) && (iNewLevel>iMaxLevel);
+  }
+  if( rc!=SQLITE_OK ) goto finished;
+
+  assert( csr.nSegment>0 );
+  assert( iNewLevel>=getAbsoluteLevel(p, iLangid, iIndex, 0) );
+  assert( iNewLevel<getAbsoluteLevel(p, iLangid, iIndex,FTS3_SEGDIR_MAXLEVEL) );
+
+  memset(&filter, 0, sizeof(Fts3SegFilter));
+  filter.flags = FTS3_SEGMENT_REQUIRE_POS;
+  filter.flags |= (bIgnoreEmpty ? FTS3_SEGMENT_IGNORE_EMPTY : 0);
+
+  rc = sqlite3Fts3SegReaderStart(p, &csr, &filter);
+  while( SQLITE_OK==rc ){
+    rc = sqlite3Fts3SegReaderStep(p, &csr);
+    if( rc!=SQLITE_ROW ) break;
+    rc = fts3SegWriterAdd(p, &pWriter, 1, 
+        csr.zTerm, csr.nTerm, csr.aDoclist, csr.nDoclist);
+  }
+  if( rc!=SQLITE_OK ) goto finished;
+  assert( pWriter || bIgnoreEmpty );
+
+  if( iLevel!=FTS3_SEGCURSOR_PENDING ){
+    rc = fts3DeleteSegdir(
+        p, iLangid, iIndex, iLevel, csr.apSegment, csr.nSegment
+    );
+    if( rc!=SQLITE_OK ) goto finished;
+  }
+  if( pWriter ){
+    rc = fts3SegWriterFlush(p, pWriter, iNewLevel, iIdx);
+    if( rc==SQLITE_OK ){
+      if( iLevel==FTS3_SEGCURSOR_PENDING || iNewLevel<iMaxLevel ){
+        rc = fts3PromoteSegments(p, iNewLevel, pWriter->nLeafData);
+      }
+    }
+  }
+
+ finished:
+  fts3SegWriterFree(pWriter);
+  sqlite3Fts3SegReaderFinish(&csr);
+  return rc;
+}
+
+
+/* 
+** Flush the contents of pendingTerms to level 0 segments. 
+*/
+int sqlite3Fts3PendingTermsFlush(Fts3Table *p){
+  int rc = SQLITE_OK;
+  int i;
+        
+  for(i=0; rc==SQLITE_OK && i<p->nIndex; i++){
+    rc = fts3SegmentMerge(p, p->iPrevLangid, i, FTS3_SEGCURSOR_PENDING);
+    if( rc==SQLITE_DONE ) rc = SQLITE_OK;
+  }
+  sqlite3Fts3PendingTermsClear(p);
+
+  /* Determine the auto-incr-merge setting if unknown.  If enabled,
+  ** estimate the number of leaf blocks of content to be written
+  */
+  if( rc==SQLITE_OK && p->bHasStat
+   && p->nAutoincrmerge==0xff && p->nLeafAdd>0
+  ){
+    sqlite3_stmt *pStmt = 0;
+    rc = fts3SqlStmt(p, SQL_SELECT_STAT, &pStmt, 0);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_int(pStmt, 1, FTS_STAT_AUTOINCRMERGE);
+      rc = sqlite3_step(pStmt);
+      if( rc==SQLITE_ROW ){
+        p->nAutoincrmerge = sqlite3_column_int(pStmt, 0);
+        if( p->nAutoincrmerge==1 ) p->nAutoincrmerge = 8;
+      }else if( rc==SQLITE_DONE ){
+        p->nAutoincrmerge = 0;
+      }
+      rc = sqlite3_reset(pStmt);
+    }
+  }
+  return rc;
+}
+
+/*
+** Encode N integers as varints into a blob.
+*/
+static void fts3EncodeIntArray(
+  int N,             /* The number of integers to encode */
+  u32 *a,            /* The integer values */
+  char *zBuf,        /* Write the BLOB here */
+  int *pNBuf         /* Write number of bytes if zBuf[] used here */
+){
+  int i, j;
+  for(i=j=0; i<N; i++){
+    j += sqlite3Fts3PutVarint(&zBuf[j], (sqlite3_int64)a[i]);
+  }
+  *pNBuf = j;
+}
+
+/*
+** Decode a blob of varints into N integers
+*/
+static void fts3DecodeIntArray(
+  int N,             /* The number of integers to decode */
+  u32 *a,            /* Write the integer values */
+  const char *zBuf,  /* The BLOB containing the varints */
+  int nBuf           /* size of the BLOB */
+){
+  int i, j;
+  UNUSED_PARAMETER(nBuf);
+  for(i=j=0; i<N; i++){
+    sqlite3_int64 x;
+    j += sqlite3Fts3GetVarint(&zBuf[j], &x);
+    assert(j<=nBuf);
+    a[i] = (u32)(x & 0xffffffff);
+  }
+}
+
+/*
+** Insert the sizes (in tokens) for each column of the document
+** with docid equal to p->iPrevDocid.  The sizes are encoded as
+** a blob of varints.
+*/
+static void fts3InsertDocsize(
+  int *pRC,                       /* Result code */
+  Fts3Table *p,                   /* Table into which to insert */
+  u32 *aSz                        /* Sizes of each column, in tokens */
+){
+  char *pBlob;             /* The BLOB encoding of the document size */
+  int nBlob;               /* Number of bytes in the BLOB */
+  sqlite3_stmt *pStmt;     /* Statement used to insert the encoding */
+  int rc;                  /* Result code from subfunctions */
+
+  if( *pRC ) return;
+  pBlob = sqlite3_malloc( 10*p->nColumn );
+  if( pBlob==0 ){
+    *pRC = SQLITE_NOMEM;
+    return;
+  }
+  fts3EncodeIntArray(p->nColumn, aSz, pBlob, &nBlob);
+  rc = fts3SqlStmt(p, SQL_REPLACE_DOCSIZE, &pStmt, 0);
+  if( rc ){
+    sqlite3_free(pBlob);
+    *pRC = rc;
+    return;
+  }
+  sqlite3_bind_int64(pStmt, 1, p->iPrevDocid);
+  sqlite3_bind_blob(pStmt, 2, pBlob, nBlob, sqlite3_free);
+  sqlite3_step(pStmt);
+  *pRC = sqlite3_reset(pStmt);
+}
+
+/*
+** Record 0 of the %_stat table contains a blob consisting of N varints,
+** where N is the number of user defined columns in the fts3 table plus
+** two. If nCol is the number of user defined columns, then values of the 
+** varints are set as follows:
+**
+**   Varint 0:       Total number of rows in the table.
+**
+**   Varint 1..nCol: For each column, the total number of tokens stored in
+**                   the column for all rows of the table.
+**
+**   Varint 1+nCol:  The total size, in bytes, of all text values in all
+**                   columns of all rows of the table.
+**
+*/
+static void fts3UpdateDocTotals(
+  int *pRC,                       /* The result code */
+  Fts3Table *p,                   /* Table being updated */
+  u32 *aSzIns,                    /* Size increases */
+  u32 *aSzDel,                    /* Size decreases */
+  int nChng                       /* Change in the number of documents */
+){
+  char *pBlob;             /* Storage for BLOB written into %_stat */
+  int nBlob;               /* Size of BLOB written into %_stat */
+  u32 *a;                  /* Array of integers that becomes the BLOB */
+  sqlite3_stmt *pStmt;     /* Statement for reading and writing */
+  int i;                   /* Loop counter */
+  int rc;                  /* Result code from subfunctions */
+
+  const int nStat = p->nColumn+2;
+
+  if( *pRC ) return;
+  a = sqlite3_malloc( (sizeof(u32)+10)*nStat );
+  if( a==0 ){
+    *pRC = SQLITE_NOMEM;
+    return;
+  }
+  pBlob = (char*)&a[nStat];
+  rc = fts3SqlStmt(p, SQL_SELECT_STAT, &pStmt, 0);
+  if( rc ){
+    sqlite3_free(a);
+    *pRC = rc;
+    return;
+  }
+  sqlite3_bind_int(pStmt, 1, FTS_STAT_DOCTOTAL);
+  if( sqlite3_step(pStmt)==SQLITE_ROW ){
+    fts3DecodeIntArray(nStat, a,
+         sqlite3_column_blob(pStmt, 0),
+         sqlite3_column_bytes(pStmt, 0));
+  }else{
+    memset(a, 0, sizeof(u32)*(nStat) );
+  }
+  rc = sqlite3_reset(pStmt);
+  if( rc!=SQLITE_OK ){
+    sqlite3_free(a);
+    *pRC = rc;
+    return;
+  }
+  if( nChng<0 && a[0]<(u32)(-nChng) ){
+    a[0] = 0;
+  }else{
+    a[0] += nChng;
+  }
+  for(i=0; i<p->nColumn+1; i++){
+    u32 x = a[i+1];
+    if( x+aSzIns[i] < aSzDel[i] ){
+      x = 0;
+    }else{
+      x = x + aSzIns[i] - aSzDel[i];
+    }
+    a[i+1] = x;
+  }
+  fts3EncodeIntArray(nStat, a, pBlob, &nBlob);
+  rc = fts3SqlStmt(p, SQL_REPLACE_STAT, &pStmt, 0);
+  if( rc ){
+    sqlite3_free(a);
+    *pRC = rc;
+    return;
+  }
+  sqlite3_bind_int(pStmt, 1, FTS_STAT_DOCTOTAL);
+  sqlite3_bind_blob(pStmt, 2, pBlob, nBlob, SQLITE_STATIC);
+  sqlite3_step(pStmt);
+  *pRC = sqlite3_reset(pStmt);
+  sqlite3_free(a);
+}
+
+/*
+** Merge the entire database so that there is one segment for each 
+** iIndex/iLangid combination.
+*/
+static int fts3DoOptimize(Fts3Table *p, int bReturnDone){
+  int bSeenDone = 0;
+  int rc;
+  sqlite3_stmt *pAllLangid = 0;
+
+  rc = fts3SqlStmt(p, SQL_SELECT_ALL_LANGID, &pAllLangid, 0);
+  if( rc==SQLITE_OK ){
+    int rc2;
+    sqlite3_bind_int(pAllLangid, 1, p->iPrevLangid);
+    sqlite3_bind_int(pAllLangid, 2, p->nIndex);
+    while( sqlite3_step(pAllLangid)==SQLITE_ROW ){
+      int i;
+      int iLangid = sqlite3_column_int(pAllLangid, 0);
+      for(i=0; rc==SQLITE_OK && i<p->nIndex; i++){
+        rc = fts3SegmentMerge(p, iLangid, i, FTS3_SEGCURSOR_ALL);
+        if( rc==SQLITE_DONE ){
+          bSeenDone = 1;
+          rc = SQLITE_OK;
+        }
+      }
+    }
+    rc2 = sqlite3_reset(pAllLangid);
+    if( rc==SQLITE_OK ) rc = rc2;
+  }
+
+  sqlite3Fts3SegmentsClose(p);
+  sqlite3Fts3PendingTermsClear(p);
+
+  return (rc==SQLITE_OK && bReturnDone && bSeenDone) ? SQLITE_DONE : rc;
+}
+
+/*
+** This function is called when the user executes the following statement:
+**
+**     INSERT INTO <tbl>(<tbl>) VALUES('rebuild');
+**
+** The entire FTS index is discarded and rebuilt. If the table is one 
+** created using the content=xxx option, then the new index is based on
+** the current contents of the xxx table. Otherwise, it is rebuilt based
+** on the contents of the %_content table.
+*/
+static int fts3DoRebuild(Fts3Table *p){
+  int rc;                         /* Return Code */
+
+  rc = fts3DeleteAll(p, 0);
+  if( rc==SQLITE_OK ){
+    u32 *aSz = 0;
+    u32 *aSzIns = 0;
+    u32 *aSzDel = 0;
+    sqlite3_stmt *pStmt = 0;
+    int nEntry = 0;
+
+    /* Compose and prepare an SQL statement to loop through the content table */
+    char *zSql = sqlite3_mprintf("SELECT %s" , p->zReadExprlist);
+    if( !zSql ){
+      rc = SQLITE_NOMEM;
+    }else{
+      rc = sqlite3_prepare_v2(p->db, zSql, -1, &pStmt, 0);
+      sqlite3_free(zSql);
+    }
+
+    if( rc==SQLITE_OK ){
+      int nByte = sizeof(u32) * (p->nColumn+1)*3;
+      aSz = (u32 *)sqlite3_malloc(nByte);
+      if( aSz==0 ){
+        rc = SQLITE_NOMEM;
+      }else{
+        memset(aSz, 0, nByte);
+        aSzIns = &aSz[p->nColumn+1];
+        aSzDel = &aSzIns[p->nColumn+1];
+      }
+    }
+
+    while( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+      int iCol;
+      int iLangid = langidFromSelect(p, pStmt);
+      rc = fts3PendingTermsDocid(p, 0, iLangid, sqlite3_column_int64(pStmt, 0));
+      memset(aSz, 0, sizeof(aSz[0]) * (p->nColumn+1));
+      for(iCol=0; rc==SQLITE_OK && iCol<p->nColumn; iCol++){
+        if( p->abNotindexed[iCol]==0 ){
+          const char *z = (const char *) sqlite3_column_text(pStmt, iCol+1);
+          rc = fts3PendingTermsAdd(p, iLangid, z, iCol, &aSz[iCol]);
+          aSz[p->nColumn] += sqlite3_column_bytes(pStmt, iCol+1);
+        }
+      }
+      if( p->bHasDocsize ){
+        fts3InsertDocsize(&rc, p, aSz);
+      }
+      if( rc!=SQLITE_OK ){
+        sqlite3_finalize(pStmt);
+        pStmt = 0;
+      }else{
+        nEntry++;
+        for(iCol=0; iCol<=p->nColumn; iCol++){
+          aSzIns[iCol] += aSz[iCol];
+        }
+      }
+    }
+    if( p->bFts4 ){
+      fts3UpdateDocTotals(&rc, p, aSzIns, aSzDel, nEntry);
+    }
+    sqlite3_free(aSz);
+
+    if( pStmt ){
+      int rc2 = sqlite3_finalize(pStmt);
+      if( rc==SQLITE_OK ){
+        rc = rc2;
+      }
+    }
+  }
+
+  return rc;
+}
+
+
+/*
+** This function opens a cursor used to read the input data for an 
+** incremental merge operation. Specifically, it opens a cursor to scan
+** the oldest nSeg segments (idx=0 through idx=(nSeg-1)) in absolute 
+** level iAbsLevel.
+*/
+static int fts3IncrmergeCsr(
+  Fts3Table *p,                   /* FTS3 table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute level to open */
+  int nSeg,                       /* Number of segments to merge */
+  Fts3MultiSegReader *pCsr        /* Cursor object to populate */
+){
+  int rc;                         /* Return Code */
+  sqlite3_stmt *pStmt = 0;        /* Statement used to read %_segdir entry */  
+  int nByte;                      /* Bytes allocated at pCsr->apSegment[] */
+
+  /* Allocate space for the Fts3MultiSegReader.aCsr[] array */
+  memset(pCsr, 0, sizeof(*pCsr));
+  nByte = sizeof(Fts3SegReader *) * nSeg;
+  pCsr->apSegment = (Fts3SegReader **)sqlite3_malloc(nByte);
+
+  if( pCsr->apSegment==0 ){
+    rc = SQLITE_NOMEM;
+  }else{
+    memset(pCsr->apSegment, 0, nByte);
+    rc = fts3SqlStmt(p, SQL_SELECT_LEVEL, &pStmt, 0);
+  }
+  if( rc==SQLITE_OK ){
+    int i;
+    int rc2;
+    sqlite3_bind_int64(pStmt, 1, iAbsLevel);
+    assert( pCsr->nSegment==0 );
+    for(i=0; rc==SQLITE_OK && sqlite3_step(pStmt)==SQLITE_ROW && i<nSeg; i++){
+      rc = sqlite3Fts3SegReaderNew(i, 0,
+          sqlite3_column_int64(pStmt, 1),        /* segdir.start_block */
+          sqlite3_column_int64(pStmt, 2),        /* segdir.leaves_end_block */
+          sqlite3_column_int64(pStmt, 3),        /* segdir.end_block */
+          sqlite3_column_blob(pStmt, 4),         /* segdir.root */
+          sqlite3_column_bytes(pStmt, 4),        /* segdir.root */
+          &pCsr->apSegment[i]
+      );
+      pCsr->nSegment++;
+    }
+    rc2 = sqlite3_reset(pStmt);
+    if( rc==SQLITE_OK ) rc = rc2;
+  }
+
+  return rc;
+}
+
+typedef struct IncrmergeWriter IncrmergeWriter;
+typedef struct NodeWriter NodeWriter;
+typedef struct Blob Blob;
+typedef struct NodeReader NodeReader;
+
+/*
+** An instance of the following structure is used as a dynamic buffer
+** to build up nodes or other blobs of data in.
+**
+** The function blobGrowBuffer() is used to extend the allocation.
+*/
+struct Blob {
+  char *a;                        /* Pointer to allocation */
+  int n;                          /* Number of valid bytes of data in a[] */
+  int nAlloc;                     /* Allocated size of a[] (nAlloc>=n) */
+};
+
+/*
+** This structure is used to build up buffers containing segment b-tree 
+** nodes (blocks).
+*/
+struct NodeWriter {
+  sqlite3_int64 iBlock;           /* Current block id */
+  Blob key;                       /* Last key written to the current block */
+  Blob block;                     /* Current block image */
+};
+
+/*
+** An object of this type contains the state required to create or append
+** to an appendable b-tree segment.
+*/
+struct IncrmergeWriter {
+  int nLeafEst;                   /* Space allocated for leaf blocks */
+  int nWork;                      /* Number of leaf pages flushed */
+  sqlite3_int64 iAbsLevel;        /* Absolute level of input segments */
+  int iIdx;                       /* Index of *output* segment in iAbsLevel+1 */
+  sqlite3_int64 iStart;           /* Block number of first allocated block */
+  sqlite3_int64 iEnd;             /* Block number of last allocated block */
+  sqlite3_int64 nLeafData;        /* Bytes of leaf page data so far */
+  u8 bNoLeafData;                 /* If true, store 0 for segment size */
+  NodeWriter aNodeWriter[FTS_MAX_APPENDABLE_HEIGHT];
+};
+
+/*
+** An object of the following type is used to read data from a single
+** FTS segment node. See the following functions:
+**
+**     nodeReaderInit()
+**     nodeReaderNext()
+**     nodeReaderRelease()
+*/
+struct NodeReader {
+  const char *aNode;
+  int nNode;
+  int iOff;                       /* Current offset within aNode[] */
+
+  /* Output variables. Containing the current node entry. */
+  sqlite3_int64 iChild;           /* Pointer to child node */
+  Blob term;                      /* Current term */
+  const char *aDoclist;           /* Pointer to doclist */
+  int nDoclist;                   /* Size of doclist in bytes */
+};
+
+/*
+** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
+** Otherwise, if the allocation at pBlob->a is not already at least nMin
+** bytes in size, extend (realloc) it to be so.
+**
+** If an OOM error occurs, set *pRc to SQLITE_NOMEM and leave pBlob->a
+** unmodified. Otherwise, if the allocation succeeds, update pBlob->nAlloc
+** to reflect the new size of the pBlob->a[] buffer.
+*/
+static void blobGrowBuffer(Blob *pBlob, int nMin, int *pRc){
+  if( *pRc==SQLITE_OK && nMin>pBlob->nAlloc ){
+    int nAlloc = nMin;
+    char *a = (char *)sqlite3_realloc(pBlob->a, nAlloc);
+    if( a ){
+      pBlob->nAlloc = nAlloc;
+      pBlob->a = a;
+    }else{
+      *pRc = SQLITE_NOMEM;
+    }
+  }
+}
+
+/*
+** Attempt to advance the node-reader object passed as the first argument to
+** the next entry on the node. 
+**
+** Return an error code if an error occurs (SQLITE_NOMEM is possible). 
+** Otherwise return SQLITE_OK. If there is no next entry on the node
+** (e.g. because the current entry is the last) set NodeReader->aNode to
+** NULL to indicate EOF. Otherwise, populate the NodeReader structure output 
+** variables for the new entry.
+*/
+static int nodeReaderNext(NodeReader *p){
+  int bFirst = (p->term.n==0);    /* True for first term on the node */
+  int nPrefix = 0;                /* Bytes to copy from previous term */
+  int nSuffix = 0;                /* Bytes to append to the prefix */
+  int rc = SQLITE_OK;             /* Return code */
+
+  assert( p->aNode );
+  if( p->iChild && bFirst==0 ) p->iChild++;
+  if( p->iOff>=p->nNode ){
+    /* EOF */
+    p->aNode = 0;
+  }else{
+    if( bFirst==0 ){
+      p->iOff += fts3GetVarint32(&p->aNode[p->iOff], &nPrefix);
+    }
+    p->iOff += fts3GetVarint32(&p->aNode[p->iOff], &nSuffix);
+
+    blobGrowBuffer(&p->term, nPrefix+nSuffix, &rc);
+    if( rc==SQLITE_OK ){
+      memcpy(&p->term.a[nPrefix], &p->aNode[p->iOff], nSuffix);
+      p->term.n = nPrefix+nSuffix;
+      p->iOff += nSuffix;
+      if( p->iChild==0 ){
+        p->iOff += fts3GetVarint32(&p->aNode[p->iOff], &p->nDoclist);
+        p->aDoclist = &p->aNode[p->iOff];
+        p->iOff += p->nDoclist;
+      }
+    }
+  }
+
+  assert( p->iOff<=p->nNode );
+
+  return rc;
+}
+
+/*
+** Release all dynamic resources held by node-reader object *p.
+*/
+static void nodeReaderRelease(NodeReader *p){
+  sqlite3_free(p->term.a);
+}
+
+/*
+** Initialize a node-reader object to read the node in buffer aNode/nNode.
+**
+** If successful, SQLITE_OK is returned and the NodeReader object set to 
+** point to the first entry on the node (if any). Otherwise, an SQLite
+** error code is returned.
+*/
+static int nodeReaderInit(NodeReader *p, const char *aNode, int nNode){
+  memset(p, 0, sizeof(NodeReader));
+  p->aNode = aNode;
+  p->nNode = nNode;
+
+  /* Figure out if this is a leaf or an internal node. */
+  if( p->aNode[0] ){
+    /* An internal node. */
+    p->iOff = 1 + sqlite3Fts3GetVarint(&p->aNode[1], &p->iChild);
+  }else{
+    p->iOff = 1;
+  }
+
+  return nodeReaderNext(p);
+}
+
+/*
+** This function is called while writing an FTS segment each time a leaf o
+** node is finished and written to disk. The key (zTerm/nTerm) is guaranteed
+** to be greater than the largest key on the node just written, but smaller
+** than or equal to the first key that will be written to the next leaf
+** node.
+**
+** The block id of the leaf node just written to disk may be found in
+** (pWriter->aNodeWriter[0].iBlock) when this function is called.
+*/
+static int fts3IncrmergePush(
+  Fts3Table *p,                   /* Fts3 table handle */
+  IncrmergeWriter *pWriter,       /* Writer object */
+  const char *zTerm,              /* Term to write to internal node */
+  int nTerm                       /* Bytes at zTerm */
+){
+  sqlite3_int64 iPtr = pWriter->aNodeWriter[0].iBlock;
+  int iLayer;
+
+  assert( nTerm>0 );
+  for(iLayer=1; ALWAYS(iLayer<FTS_MAX_APPENDABLE_HEIGHT); iLayer++){
+    sqlite3_int64 iNextPtr = 0;
+    NodeWriter *pNode = &pWriter->aNodeWriter[iLayer];
+    int rc = SQLITE_OK;
+    int nPrefix;
+    int nSuffix;
+    int nSpace;
+
+    /* Figure out how much space the key will consume if it is written to
+    ** the current node of layer iLayer. Due to the prefix compression, 
+    ** the space required changes depending on which node the key is to
+    ** be added to.  */
+    nPrefix = fts3PrefixCompress(pNode->key.a, pNode->key.n, zTerm, nTerm);
+    nSuffix = nTerm - nPrefix;
+    nSpace  = sqlite3Fts3VarintLen(nPrefix);
+    nSpace += sqlite3Fts3VarintLen(nSuffix) + nSuffix;
+
+    if( pNode->key.n==0 || (pNode->block.n + nSpace)<=p->nNodeSize ){ 
+      /* If the current node of layer iLayer contains zero keys, or if adding
+      ** the key to it will not cause it to grow to larger than nNodeSize 
+      ** bytes in size, write the key here.  */
+
+      Blob *pBlk = &pNode->block;
+      if( pBlk->n==0 ){
+        blobGrowBuffer(pBlk, p->nNodeSize, &rc);
+        if( rc==SQLITE_OK ){
+          pBlk->a[0] = (char)iLayer;
+          pBlk->n = 1 + sqlite3Fts3PutVarint(&pBlk->a[1], iPtr);
+        }
+      }
+      blobGrowBuffer(pBlk, pBlk->n + nSpace, &rc);
+      blobGrowBuffer(&pNode->key, nTerm, &rc);
+
+      if( rc==SQLITE_OK ){
+        if( pNode->key.n ){
+          pBlk->n += sqlite3Fts3PutVarint(&pBlk->a[pBlk->n], nPrefix);
+        }
+        pBlk->n += sqlite3Fts3PutVarint(&pBlk->a[pBlk->n], nSuffix);
+        memcpy(&pBlk->a[pBlk->n], &zTerm[nPrefix], nSuffix);
+        pBlk->n += nSuffix;
+
+        memcpy(pNode->key.a, zTerm, nTerm);
+        pNode->key.n = nTerm;
+      }
+    }else{
+      /* Otherwise, flush the current node of layer iLayer to disk.
+      ** Then allocate a new, empty sibling node. The key will be written
+      ** into the parent of this node. */
+      rc = fts3WriteSegment(p, pNode->iBlock, pNode->block.a, pNode->block.n);
+
+      assert( pNode->block.nAlloc>=p->nNodeSize );
+      pNode->block.a[0] = (char)iLayer;
+      pNode->block.n = 1 + sqlite3Fts3PutVarint(&pNode->block.a[1], iPtr+1);
+
+      iNextPtr = pNode->iBlock;
+      pNode->iBlock++;
+      pNode->key.n = 0;
+    }
+
+    if( rc!=SQLITE_OK || iNextPtr==0 ) return rc;
+    iPtr = iNextPtr;
+  }
+
+  assert( 0 );
+  return 0;
+}
+
+/*
+** Append a term and (optionally) doclist to the FTS segment node currently
+** stored in blob *pNode. The node need not contain any terms, but the
+** header must be written before this function is called.
+**
+** A node header is a single 0x00 byte for a leaf node, or a height varint
+** followed by the left-hand-child varint for an internal node.
+**
+** The term to be appended is passed via arguments zTerm/nTerm. For a 
+** leaf node, the doclist is passed as aDoclist/nDoclist. For an internal
+** node, both aDoclist and nDoclist must be passed 0.
+**
+** If the size of the value in blob pPrev is zero, then this is the first
+** term written to the node. Otherwise, pPrev contains a copy of the 
+** previous term. Before this function returns, it is updated to contain a
+** copy of zTerm/nTerm.
+**
+** It is assumed that the buffer associated with pNode is already large
+** enough to accommodate the new entry. The buffer associated with pPrev
+** is extended by this function if requrired.
+**
+** If an error (i.e. OOM condition) occurs, an SQLite error code is
+** returned. Otherwise, SQLITE_OK.
+*/
+static int fts3AppendToNode(
+  Blob *pNode,                    /* Current node image to append to */
+  Blob *pPrev,                    /* Buffer containing previous term written */
+  const char *zTerm,              /* New term to write */
+  int nTerm,                      /* Size of zTerm in bytes */
+  const char *aDoclist,           /* Doclist (or NULL) to write */
+  int nDoclist                    /* Size of aDoclist in bytes */ 
+){
+  int rc = SQLITE_OK;             /* Return code */
+  int bFirst = (pPrev->n==0);     /* True if this is the first term written */
+  int nPrefix;                    /* Size of term prefix in bytes */
+  int nSuffix;                    /* Size of term suffix in bytes */
+
+  /* Node must have already been started. There must be a doclist for a
+  ** leaf node, and there must not be a doclist for an internal node.  */
+  assert( pNode->n>0 );
+  assert( (pNode->a[0]=='\0')==(aDoclist!=0) );
+
+  blobGrowBuffer(pPrev, nTerm, &rc);
+  if( rc!=SQLITE_OK ) return rc;
+
+  nPrefix = fts3PrefixCompress(pPrev->a, pPrev->n, zTerm, nTerm);
+  nSuffix = nTerm - nPrefix;
+  memcpy(pPrev->a, zTerm, nTerm);
+  pPrev->n = nTerm;
+
+  if( bFirst==0 ){
+    pNode->n += sqlite3Fts3PutVarint(&pNode->a[pNode->n], nPrefix);
+  }
+  pNode->n += sqlite3Fts3PutVarint(&pNode->a[pNode->n], nSuffix);
+  memcpy(&pNode->a[pNode->n], &zTerm[nPrefix], nSuffix);
+  pNode->n += nSuffix;
+
+  if( aDoclist ){
+    pNode->n += sqlite3Fts3PutVarint(&pNode->a[pNode->n], nDoclist);
+    memcpy(&pNode->a[pNode->n], aDoclist, nDoclist);
+    pNode->n += nDoclist;
+  }
+
+  assert( pNode->n<=pNode->nAlloc );
+
+  return SQLITE_OK;
+}
+
+/*
+** Append the current term and doclist pointed to by cursor pCsr to the
+** appendable b-tree segment opened for writing by pWriter.
+**
+** Return SQLITE_OK if successful, or an SQLite error code otherwise.
+*/
+static int fts3IncrmergeAppend(
+  Fts3Table *p,                   /* Fts3 table handle */
+  IncrmergeWriter *pWriter,       /* Writer object */
+  Fts3MultiSegReader *pCsr        /* Cursor containing term and doclist */
+){
+  const char *zTerm = pCsr->zTerm;
+  int nTerm = pCsr->nTerm;
+  const char *aDoclist = pCsr->aDoclist;
+  int nDoclist = pCsr->nDoclist;
+  int rc = SQLITE_OK;           /* Return code */
+  int nSpace;                   /* Total space in bytes required on leaf */
+  int nPrefix;                  /* Size of prefix shared with previous term */
+  int nSuffix;                  /* Size of suffix (nTerm - nPrefix) */
+  NodeWriter *pLeaf;            /* Object used to write leaf nodes */
+
+  pLeaf = &pWriter->aNodeWriter[0];
+  nPrefix = fts3PrefixCompress(pLeaf->key.a, pLeaf->key.n, zTerm, nTerm);
+  nSuffix = nTerm - nPrefix;
+
+  nSpace  = sqlite3Fts3VarintLen(nPrefix);
+  nSpace += sqlite3Fts3VarintLen(nSuffix) + nSuffix;
+  nSpace += sqlite3Fts3VarintLen(nDoclist) + nDoclist;
+
+  /* If the current block is not empty, and if adding this term/doclist
+  ** to the current block would make it larger than Fts3Table.nNodeSize
+  ** bytes, write this block out to the database. */
+  if( pLeaf->block.n>0 && (pLeaf->block.n + nSpace)>p->nNodeSize ){
+    rc = fts3WriteSegment(p, pLeaf->iBlock, pLeaf->block.a, pLeaf->block.n);
+    pWriter->nWork++;
+
+    /* Add the current term to the parent node. The term added to the 
+    ** parent must:
+    **
+    **   a) be greater than the largest term on the leaf node just written
+    **      to the database (still available in pLeaf->key), and
+    **
+    **   b) be less than or equal to the term about to be added to the new
+    **      leaf node (zTerm/nTerm).
+    **
+    ** In other words, it must be the prefix of zTerm 1 byte longer than
+    ** the common prefix (if any) of zTerm and pWriter->zTerm.
+    */
+    if( rc==SQLITE_OK ){
+      rc = fts3IncrmergePush(p, pWriter, zTerm, nPrefix+1);
+    }
+
+    /* Advance to the next output block */
+    pLeaf->iBlock++;
+    pLeaf->key.n = 0;
+    pLeaf->block.n = 0;
+
+    nSuffix = nTerm;
+    nSpace  = 1;
+    nSpace += sqlite3Fts3VarintLen(nSuffix) + nSuffix;
+    nSpace += sqlite3Fts3VarintLen(nDoclist) + nDoclist;
+  }
+
+  pWriter->nLeafData += nSpace;
+  blobGrowBuffer(&pLeaf->block, pLeaf->block.n + nSpace, &rc);
+  if( rc==SQLITE_OK ){
+    if( pLeaf->block.n==0 ){
+      pLeaf->block.n = 1;
+      pLeaf->block.a[0] = '\0';
+    }
+    rc = fts3AppendToNode(
+        &pLeaf->block, &pLeaf->key, zTerm, nTerm, aDoclist, nDoclist
+    );
+  }
+
+  return rc;
+}
+
+/*
+** This function is called to release all dynamic resources held by the
+** merge-writer object pWriter, and if no error has occurred, to flush
+** all outstanding node buffers held by pWriter to disk.
+**
+** If *pRc is not SQLITE_OK when this function is called, then no attempt
+** is made to write any data to disk. Instead, this function serves only
+** to release outstanding resources.
+**
+** Otherwise, if *pRc is initially SQLITE_OK and an error occurs while
+** flushing buffers to disk, *pRc is set to an SQLite error code before
+** returning.
+*/
+static void fts3IncrmergeRelease(
+  Fts3Table *p,                   /* FTS3 table handle */
+  IncrmergeWriter *pWriter,       /* Merge-writer object */
+  int *pRc                        /* IN/OUT: Error code */
+){
+  int i;                          /* Used to iterate through non-root layers */
+  int iRoot;                      /* Index of root in pWriter->aNodeWriter */
+  NodeWriter *pRoot;              /* NodeWriter for root node */
+  int rc = *pRc;                  /* Error code */
+
+  /* Set iRoot to the index in pWriter->aNodeWriter[] of the output segment 
+  ** root node. If the segment fits entirely on a single leaf node, iRoot
+  ** will be set to 0. If the root node is the parent of the leaves, iRoot
+  ** will be 1. And so on.  */
+  for(iRoot=FTS_MAX_APPENDABLE_HEIGHT-1; iRoot>=0; iRoot--){
+    NodeWriter *pNode = &pWriter->aNodeWriter[iRoot];
+    if( pNode->block.n>0 ) break;
+    assert( *pRc || pNode->block.nAlloc==0 );
+    assert( *pRc || pNode->key.nAlloc==0 );
+    sqlite3_free(pNode->block.a);
+    sqlite3_free(pNode->key.a);
+  }
+
+  /* Empty output segment. This is a no-op. */
+  if( iRoot<0 ) return;
+
+  /* The entire output segment fits on a single node. Normally, this means
+  ** the node would be stored as a blob in the "root" column of the %_segdir
+  ** table. However, this is not permitted in this case. The problem is that 
+  ** space has already been reserved in the %_segments table, and so the 
+  ** start_block and end_block fields of the %_segdir table must be populated. 
+  ** And, by design or by accident, released versions of FTS cannot handle 
+  ** segments that fit entirely on the root node with start_block!=0.
+  **
+  ** Instead, create a synthetic root node that contains nothing but a 
+  ** pointer to the single content node. So that the segment consists of a
+  ** single leaf and a single interior (root) node.
+  **
+  ** Todo: Better might be to defer allocating space in the %_segments 
+  ** table until we are sure it is needed.
+  */
+  if( iRoot==0 ){
+    Blob *pBlock = &pWriter->aNodeWriter[1].block;
+    blobGrowBuffer(pBlock, 1 + FTS3_VARINT_MAX, &rc);
+    if( rc==SQLITE_OK ){
+      pBlock->a[0] = 0x01;
+      pBlock->n = 1 + sqlite3Fts3PutVarint(
+          &pBlock->a[1], pWriter->aNodeWriter[0].iBlock
+      );
+    }
+    iRoot = 1;
+  }
+  pRoot = &pWriter->aNodeWriter[iRoot];
+
+  /* Flush all currently outstanding nodes to disk. */
+  for(i=0; i<iRoot; i++){
+    NodeWriter *pNode = &pWriter->aNodeWriter[i];
+    if( pNode->block.n>0 && rc==SQLITE_OK ){
+      rc = fts3WriteSegment(p, pNode->iBlock, pNode->block.a, pNode->block.n);
+    }
+    sqlite3_free(pNode->block.a);
+    sqlite3_free(pNode->key.a);
+  }
+
+  /* Write the %_segdir record. */
+  if( rc==SQLITE_OK ){
+    rc = fts3WriteSegdir(p, 
+        pWriter->iAbsLevel+1,               /* level */
+        pWriter->iIdx,                      /* idx */
+        pWriter->iStart,                    /* start_block */
+        pWriter->aNodeWriter[0].iBlock,     /* leaves_end_block */
+        pWriter->iEnd,                      /* end_block */
+        (pWriter->bNoLeafData==0 ? pWriter->nLeafData : 0),   /* end_block */
+        pRoot->block.a, pRoot->block.n      /* root */
+    );
+  }
+  sqlite3_free(pRoot->block.a);
+  sqlite3_free(pRoot->key.a);
+
+  *pRc = rc;
+}
+
+/*
+** Compare the term in buffer zLhs (size in bytes nLhs) with that in
+** zRhs (size in bytes nRhs) using memcmp. If one term is a prefix of
+** the other, it is considered to be smaller than the other.
+**
+** Return -ve if zLhs is smaller than zRhs, 0 if it is equal, or +ve
+** if it is greater.
+*/
+static int fts3TermCmp(
+  const char *zLhs, int nLhs,     /* LHS of comparison */
+  const char *zRhs, int nRhs      /* RHS of comparison */
+){
+  int nCmp = MIN(nLhs, nRhs);
+  int res;
+
+  res = memcmp(zLhs, zRhs, nCmp);
+  if( res==0 ) res = nLhs - nRhs;
+
+  return res;
+}
+
+
+/*
+** Query to see if the entry in the %_segments table with blockid iEnd is 
+** NULL. If no error occurs and the entry is NULL, set *pbRes 1 before
+** returning. Otherwise, set *pbRes to 0. 
+**
+** Or, if an error occurs while querying the database, return an SQLite 
+** error code. The final value of *pbRes is undefined in this case.
+**
+** This is used to test if a segment is an "appendable" segment. If it
+** is, then a NULL entry has been inserted into the %_segments table
+** with blockid %_segdir.end_block.
+*/
+static int fts3IsAppendable(Fts3Table *p, sqlite3_int64 iEnd, int *pbRes){
+  int bRes = 0;                   /* Result to set *pbRes to */
+  sqlite3_stmt *pCheck = 0;       /* Statement to query database with */
+  int rc;                         /* Return code */
+
+  rc = fts3SqlStmt(p, SQL_SEGMENT_IS_APPENDABLE, &pCheck, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pCheck, 1, iEnd);
+    if( SQLITE_ROW==sqlite3_step(pCheck) ) bRes = 1;
+    rc = sqlite3_reset(pCheck);
+  }
+  
+  *pbRes = bRes;
+  return rc;
+}
+
+/*
+** This function is called when initializing an incremental-merge operation.
+** It checks if the existing segment with index value iIdx at absolute level 
+** (iAbsLevel+1) can be appended to by the incremental merge. If it can, the
+** merge-writer object *pWriter is initialized to write to it.
+**
+** An existing segment can be appended to by an incremental merge if:
+**
+**   * It was initially created as an appendable segment (with all required
+**     space pre-allocated), and
+**
+**   * The first key read from the input (arguments zKey and nKey) is 
+**     greater than the largest key currently stored in the potential
+**     output segment.
+*/
+static int fts3IncrmergeLoad(
+  Fts3Table *p,                   /* Fts3 table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute level of input segments */
+  int iIdx,                       /* Index of candidate output segment */
+  const char *zKey,               /* First key to write */
+  int nKey,                       /* Number of bytes in nKey */
+  IncrmergeWriter *pWriter        /* Populate this object */
+){
+  int rc;                         /* Return code */
+  sqlite3_stmt *pSelect = 0;      /* SELECT to read %_segdir entry */
+
+  rc = fts3SqlStmt(p, SQL_SELECT_SEGDIR, &pSelect, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_int64 iStart = 0;     /* Value of %_segdir.start_block */
+    sqlite3_int64 iLeafEnd = 0;   /* Value of %_segdir.leaves_end_block */
+    sqlite3_int64 iEnd = 0;       /* Value of %_segdir.end_block */
+    const char *aRoot = 0;        /* Pointer to %_segdir.root buffer */
+    int nRoot = 0;                /* Size of aRoot[] in bytes */
+    int rc2;                      /* Return code from sqlite3_reset() */
+    int bAppendable = 0;          /* Set to true if segment is appendable */
+
+    /* Read the %_segdir entry for index iIdx absolute level (iAbsLevel+1) */
+    sqlite3_bind_int64(pSelect, 1, iAbsLevel+1);
+    sqlite3_bind_int(pSelect, 2, iIdx);
+    if( sqlite3_step(pSelect)==SQLITE_ROW ){
+      iStart = sqlite3_column_int64(pSelect, 1);
+      iLeafEnd = sqlite3_column_int64(pSelect, 2);
+      fts3ReadEndBlockField(pSelect, 3, &iEnd, &pWriter->nLeafData);
+      if( pWriter->nLeafData<0 ){
+        pWriter->nLeafData = pWriter->nLeafData * -1;
+      }
+      pWriter->bNoLeafData = (pWriter->nLeafData==0);
+      nRoot = sqlite3_column_bytes(pSelect, 4);
+      aRoot = sqlite3_column_blob(pSelect, 4);
+    }else{
+      return sqlite3_reset(pSelect);
+    }
+
+    /* Check for the zero-length marker in the %_segments table */
+    rc = fts3IsAppendable(p, iEnd, &bAppendable);
+
+    /* Check that zKey/nKey is larger than the largest key the candidate */
+    if( rc==SQLITE_OK && bAppendable ){
+      char *aLeaf = 0;
+      int nLeaf = 0;
+
+      rc = sqlite3Fts3ReadBlock(p, iLeafEnd, &aLeaf, &nLeaf, 0);
+      if( rc==SQLITE_OK ){
+        NodeReader reader;
+        for(rc = nodeReaderInit(&reader, aLeaf, nLeaf);
+            rc==SQLITE_OK && reader.aNode;
+            rc = nodeReaderNext(&reader)
+        ){
+          assert( reader.aNode );
+        }
+        if( fts3TermCmp(zKey, nKey, reader.term.a, reader.term.n)<=0 ){
+          bAppendable = 0;
+        }
+        nodeReaderRelease(&reader);
+      }
+      sqlite3_free(aLeaf);
+    }
+
+    if( rc==SQLITE_OK && bAppendable ){
+      /* It is possible to append to this segment. Set up the IncrmergeWriter
+      ** object to do so.  */
+      int i;
+      int nHeight = (int)aRoot[0];
+      NodeWriter *pNode;
+
+      pWriter->nLeafEst = (int)((iEnd - iStart) + 1)/FTS_MAX_APPENDABLE_HEIGHT;
+      pWriter->iStart = iStart;
+      pWriter->iEnd = iEnd;
+      pWriter->iAbsLevel = iAbsLevel;
+      pWriter->iIdx = iIdx;
+
+      for(i=nHeight+1; i<FTS_MAX_APPENDABLE_HEIGHT; i++){
+        pWriter->aNodeWriter[i].iBlock = pWriter->iStart + i*pWriter->nLeafEst;
+      }
+
+      pNode = &pWriter->aNodeWriter[nHeight];
+      pNode->iBlock = pWriter->iStart + pWriter->nLeafEst*nHeight;
+      blobGrowBuffer(&pNode->block, MAX(nRoot, p->nNodeSize), &rc);
+      if( rc==SQLITE_OK ){
+        memcpy(pNode->block.a, aRoot, nRoot);
+        pNode->block.n = nRoot;
+      }
+
+      for(i=nHeight; i>=0 && rc==SQLITE_OK; i--){
+        NodeReader reader;
+        pNode = &pWriter->aNodeWriter[i];
+
+        rc = nodeReaderInit(&reader, pNode->block.a, pNode->block.n);
+        while( reader.aNode && rc==SQLITE_OK ) rc = nodeReaderNext(&reader);
+        blobGrowBuffer(&pNode->key, reader.term.n, &rc);
+        if( rc==SQLITE_OK ){
+          memcpy(pNode->key.a, reader.term.a, reader.term.n);
+          pNode->key.n = reader.term.n;
+          if( i>0 ){
+            char *aBlock = 0;
+            int nBlock = 0;
+            pNode = &pWriter->aNodeWriter[i-1];
+            pNode->iBlock = reader.iChild;
+            rc = sqlite3Fts3ReadBlock(p, reader.iChild, &aBlock, &nBlock, 0);
+            blobGrowBuffer(&pNode->block, MAX(nBlock, p->nNodeSize), &rc);
+            if( rc==SQLITE_OK ){
+              memcpy(pNode->block.a, aBlock, nBlock);
+              pNode->block.n = nBlock;
+            }
+            sqlite3_free(aBlock);
+          }
+        }
+        nodeReaderRelease(&reader);
+      }
+    }
+
+    rc2 = sqlite3_reset(pSelect);
+    if( rc==SQLITE_OK ) rc = rc2;
+  }
+
+  return rc;
+}
+
+/*
+** Determine the largest segment index value that exists within absolute
+** level iAbsLevel+1. If no error occurs, set *piIdx to this value plus
+** one before returning SQLITE_OK. Or, if there are no segments at all 
+** within level iAbsLevel, set *piIdx to zero.
+**
+** If an error occurs, return an SQLite error code. The final value of
+** *piIdx is undefined in this case.
+*/
+static int fts3IncrmergeOutputIdx( 
+  Fts3Table *p,                   /* FTS Table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute index of input segments */
+  int *piIdx                      /* OUT: Next free index at iAbsLevel+1 */
+){
+  int rc;
+  sqlite3_stmt *pOutputIdx = 0;   /* SQL used to find output index */
+
+  rc = fts3SqlStmt(p, SQL_NEXT_SEGMENT_INDEX, &pOutputIdx, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pOutputIdx, 1, iAbsLevel+1);
+    sqlite3_step(pOutputIdx);
+    *piIdx = sqlite3_column_int(pOutputIdx, 0);
+    rc = sqlite3_reset(pOutputIdx);
+  }
+
+  return rc;
+}
+
+/* 
+** Allocate an appendable output segment on absolute level iAbsLevel+1
+** with idx value iIdx.
+**
+** In the %_segdir table, a segment is defined by the values in three
+** columns:
+**
+**     start_block
+**     leaves_end_block
+**     end_block
+**
+** When an appendable segment is allocated, it is estimated that the
+** maximum number of leaf blocks that may be required is the sum of the
+** number of leaf blocks consumed by the input segments, plus the number
+** of input segments, multiplied by two. This value is stored in stack 
+** variable nLeafEst.
+**
+** A total of 16*nLeafEst blocks are allocated when an appendable segment
+** is created ((1 + end_block - start_block)==16*nLeafEst). The contiguous
+** array of leaf nodes starts at the first block allocated. The array
+** of interior nodes that are parents of the leaf nodes start at block
+** (start_block + (1 + end_block - start_block) / 16). And so on.
+**
+** In the actual code below, the value "16" is replaced with the 
+** pre-processor macro FTS_MAX_APPENDABLE_HEIGHT.
+*/
+static int fts3IncrmergeWriter( 
+  Fts3Table *p,                   /* Fts3 table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute level of input segments */
+  int iIdx,                       /* Index of new output segment */
+  Fts3MultiSegReader *pCsr,       /* Cursor that data will be read from */
+  IncrmergeWriter *pWriter        /* Populate this object */
+){
+  int rc;                         /* Return Code */
+  int i;                          /* Iterator variable */
+  int nLeafEst = 0;               /* Blocks allocated for leaf nodes */
+  sqlite3_stmt *pLeafEst = 0;     /* SQL used to determine nLeafEst */
+  sqlite3_stmt *pFirstBlock = 0;  /* SQL used to determine first block */
+
+  /* Calculate nLeafEst. */
+  rc = fts3SqlStmt(p, SQL_MAX_LEAF_NODE_ESTIMATE, &pLeafEst, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pLeafEst, 1, iAbsLevel);
+    sqlite3_bind_int64(pLeafEst, 2, pCsr->nSegment);
+    if( SQLITE_ROW==sqlite3_step(pLeafEst) ){
+      nLeafEst = sqlite3_column_int(pLeafEst, 0);
+    }
+    rc = sqlite3_reset(pLeafEst);
+  }
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* Calculate the first block to use in the output segment */
+  rc = fts3SqlStmt(p, SQL_NEXT_SEGMENTS_ID, &pFirstBlock, 0);
+  if( rc==SQLITE_OK ){
+    if( SQLITE_ROW==sqlite3_step(pFirstBlock) ){
+      pWriter->iStart = sqlite3_column_int64(pFirstBlock, 0);
+      pWriter->iEnd = pWriter->iStart - 1;
+      pWriter->iEnd += nLeafEst * FTS_MAX_APPENDABLE_HEIGHT;
+    }
+    rc = sqlite3_reset(pFirstBlock);
+  }
+  if( rc!=SQLITE_OK ) return rc;
+
+  /* Insert the marker in the %_segments table to make sure nobody tries
+  ** to steal the space just allocated. This is also used to identify 
+  ** appendable segments.  */
+  rc = fts3WriteSegment(p, pWriter->iEnd, 0, 0);
+  if( rc!=SQLITE_OK ) return rc;
+
+  pWriter->iAbsLevel = iAbsLevel;
+  pWriter->nLeafEst = nLeafEst;
+  pWriter->iIdx = iIdx;
+
+  /* Set up the array of NodeWriter objects */
+  for(i=0; i<FTS_MAX_APPENDABLE_HEIGHT; i++){
+    pWriter->aNodeWriter[i].iBlock = pWriter->iStart + i*pWriter->nLeafEst;
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Remove an entry from the %_segdir table. This involves running the 
+** following two statements:
+**
+**   DELETE FROM %_segdir WHERE level = :iAbsLevel AND idx = :iIdx
+**   UPDATE %_segdir SET idx = idx - 1 WHERE level = :iAbsLevel AND idx > :iIdx
+**
+** The DELETE statement removes the specific %_segdir level. The UPDATE 
+** statement ensures that the remaining segments have contiguously allocated
+** idx values.
+*/
+static int fts3RemoveSegdirEntry(
+  Fts3Table *p,                   /* FTS3 table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute level to delete from */
+  int iIdx                        /* Index of %_segdir entry to delete */
+){
+  int rc;                         /* Return code */
+  sqlite3_stmt *pDelete = 0;      /* DELETE statement */
+
+  rc = fts3SqlStmt(p, SQL_DELETE_SEGDIR_ENTRY, &pDelete, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pDelete, 1, iAbsLevel);
+    sqlite3_bind_int(pDelete, 2, iIdx);
+    sqlite3_step(pDelete);
+    rc = sqlite3_reset(pDelete);
+  }
+
+  return rc;
+}
+
+/*
+** One or more segments have just been removed from absolute level iAbsLevel.
+** Update the 'idx' values of the remaining segments in the level so that
+** the idx values are a contiguous sequence starting from 0.
+*/
+static int fts3RepackSegdirLevel(
+  Fts3Table *p,                   /* FTS3 table handle */
+  sqlite3_int64 iAbsLevel         /* Absolute level to repack */
+){
+  int rc;                         /* Return code */
+  int *aIdx = 0;                  /* Array of remaining idx values */
+  int nIdx = 0;                   /* Valid entries in aIdx[] */
+  int nAlloc = 0;                 /* Allocated size of aIdx[] */
+  int i;                          /* Iterator variable */
+  sqlite3_stmt *pSelect = 0;      /* Select statement to read idx values */
+  sqlite3_stmt *pUpdate = 0;      /* Update statement to modify idx values */
+
+  rc = fts3SqlStmt(p, SQL_SELECT_INDEXES, &pSelect, 0);
+  if( rc==SQLITE_OK ){
+    int rc2;
+    sqlite3_bind_int64(pSelect, 1, iAbsLevel);
+    while( SQLITE_ROW==sqlite3_step(pSelect) ){
+      if( nIdx>=nAlloc ){
+        int *aNew;
+        nAlloc += 16;
+        aNew = sqlite3_realloc(aIdx, nAlloc*sizeof(int));
+        if( !aNew ){
+          rc = SQLITE_NOMEM;
+          break;
+        }
+        aIdx = aNew;
+      }
+      aIdx[nIdx++] = sqlite3_column_int(pSelect, 0);
+    }
+    rc2 = sqlite3_reset(pSelect);
+    if( rc==SQLITE_OK ) rc = rc2;
+  }
+
+  if( rc==SQLITE_OK ){
+    rc = fts3SqlStmt(p, SQL_SHIFT_SEGDIR_ENTRY, &pUpdate, 0);
+  }
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int64(pUpdate, 2, iAbsLevel);
+  }
+
+  assert( p->bIgnoreSavepoint==0 );
+  p->bIgnoreSavepoint = 1;
+  for(i=0; rc==SQLITE_OK && i<nIdx; i++){
+    if( aIdx[i]!=i ){
+      sqlite3_bind_int(pUpdate, 3, aIdx[i]);
+      sqlite3_bind_int(pUpdate, 1, i);
+      sqlite3_step(pUpdate);
+      rc = sqlite3_reset(pUpdate);
+    }
+  }
+  p->bIgnoreSavepoint = 0;
+
+  sqlite3_free(aIdx);
+  return rc;
+}
+
+static void fts3StartNode(Blob *pNode, int iHeight, sqlite3_int64 iChild){
+  pNode->a[0] = (char)iHeight;
+  if( iChild ){
+    assert( pNode->nAlloc>=1+sqlite3Fts3VarintLen(iChild) );
+    pNode->n = 1 + sqlite3Fts3PutVarint(&pNode->a[1], iChild);
+  }else{
+    assert( pNode->nAlloc>=1 );
+    pNode->n = 1;
+  }
+}
+
+/*
+** The first two arguments are a pointer to and the size of a segment b-tree
+** node. The node may be a leaf or an internal node.
+**
+** This function creates a new node image in blob object *pNew by copying
+** all terms that are greater than or equal to zTerm/nTerm (for leaf nodes)
+** or greater than zTerm/nTerm (for internal nodes) from aNode/nNode.
+*/
+static int fts3TruncateNode(
+  const char *aNode,              /* Current node image */
+  int nNode,                      /* Size of aNode in bytes */
+  Blob *pNew,                     /* OUT: Write new node image here */
+  const char *zTerm,              /* Omit all terms smaller than this */
+  int nTerm,                      /* Size of zTerm in bytes */
+  sqlite3_int64 *piBlock          /* OUT: Block number in next layer down */
+){
+  NodeReader reader;              /* Reader object */
+  Blob prev = {0, 0, 0};          /* Previous term written to new node */
+  int rc = SQLITE_OK;             /* Return code */
+  int bLeaf = aNode[0]=='\0';     /* True for a leaf node */
+
+  /* Allocate required output space */
+  blobGrowBuffer(pNew, nNode, &rc);
+  if( rc!=SQLITE_OK ) return rc;
+  pNew->n = 0;
+
+  /* Populate new node buffer */
+  for(rc = nodeReaderInit(&reader, aNode, nNode); 
+      rc==SQLITE_OK && reader.aNode; 
+      rc = nodeReaderNext(&reader)
+  ){
+    if( pNew->n==0 ){
+      int res = fts3TermCmp(reader.term.a, reader.term.n, zTerm, nTerm);
+      if( res<0 || (bLeaf==0 && res==0) ) continue;
+      fts3StartNode(pNew, (int)aNode[0], reader.iChild);
+      *piBlock = reader.iChild;
+    }
+    rc = fts3AppendToNode(
+        pNew, &prev, reader.term.a, reader.term.n,
+        reader.aDoclist, reader.nDoclist
+    );
+    if( rc!=SQLITE_OK ) break;
+  }
+  if( pNew->n==0 ){
+    fts3StartNode(pNew, (int)aNode[0], reader.iChild);
+    *piBlock = reader.iChild;
+  }
+  assert( pNew->n<=pNew->nAlloc );
+
+  nodeReaderRelease(&reader);
+  sqlite3_free(prev.a);
+  return rc;
+}
+
+/*
+** Remove all terms smaller than zTerm/nTerm from segment iIdx in absolute 
+** level iAbsLevel. This may involve deleting entries from the %_segments
+** table, and modifying existing entries in both the %_segments and %_segdir
+** tables.
+**
+** SQLITE_OK is returned if the segment is updated successfully. Or an
+** SQLite error code otherwise.
+*/
+static int fts3TruncateSegment(
+  Fts3Table *p,                   /* FTS3 table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute level of segment to modify */
+  int iIdx,                       /* Index within level of segment to modify */
+  const char *zTerm,              /* Remove terms smaller than this */
+  int nTerm                      /* Number of bytes in buffer zTerm */
+){
+  int rc = SQLITE_OK;             /* Return code */
+  Blob root = {0,0,0};            /* New root page image */
+  Blob block = {0,0,0};           /* Buffer used for any other block */
+  sqlite3_int64 iBlock = 0;       /* Block id */
+  sqlite3_int64 iNewStart = 0;    /* New value for iStartBlock */
+  sqlite3_int64 iOldStart = 0;    /* Old value for iStartBlock */
+  sqlite3_stmt *pFetch = 0;       /* Statement used to fetch segdir */
+
+  rc = fts3SqlStmt(p, SQL_SELECT_SEGDIR, &pFetch, 0);
+  if( rc==SQLITE_OK ){
+    int rc2;                      /* sqlite3_reset() return code */
+    sqlite3_bind_int64(pFetch, 1, iAbsLevel);
+    sqlite3_bind_int(pFetch, 2, iIdx);
+    if( SQLITE_ROW==sqlite3_step(pFetch) ){
+      const char *aRoot = sqlite3_column_blob(pFetch, 4);
+      int nRoot = sqlite3_column_bytes(pFetch, 4);
+      iOldStart = sqlite3_column_int64(pFetch, 1);
+      rc = fts3TruncateNode(aRoot, nRoot, &root, zTerm, nTerm, &iBlock);
+    }
+    rc2 = sqlite3_reset(pFetch);
+    if( rc==SQLITE_OK ) rc = rc2;
+  }
+
+  while( rc==SQLITE_OK && iBlock ){
+    char *aBlock = 0;
+    int nBlock = 0;
+    iNewStart = iBlock;
+
+    rc = sqlite3Fts3ReadBlock(p, iBlock, &aBlock, &nBlock, 0);
+    if( rc==SQLITE_OK ){
+      rc = fts3TruncateNode(aBlock, nBlock, &block, zTerm, nTerm, &iBlock);
+    }
+    if( rc==SQLITE_OK ){
+      rc = fts3WriteSegment(p, iNewStart, block.a, block.n);
+    }
+    sqlite3_free(aBlock);
+  }
+
+  /* Variable iNewStart now contains the first valid leaf node. */
+  if( rc==SQLITE_OK && iNewStart ){
+    sqlite3_stmt *pDel = 0;
+    rc = fts3SqlStmt(p, SQL_DELETE_SEGMENTS_RANGE, &pDel, 0);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_int64(pDel, 1, iOldStart);
+      sqlite3_bind_int64(pDel, 2, iNewStart-1);
+      sqlite3_step(pDel);
+      rc = sqlite3_reset(pDel);
+    }
+  }
+
+  if( rc==SQLITE_OK ){
+    sqlite3_stmt *pChomp = 0;
+    rc = fts3SqlStmt(p, SQL_CHOMP_SEGDIR, &pChomp, 0);
+    if( rc==SQLITE_OK ){
+      sqlite3_bind_int64(pChomp, 1, iNewStart);
+      sqlite3_bind_blob(pChomp, 2, root.a, root.n, SQLITE_STATIC);
+      sqlite3_bind_int64(pChomp, 3, iAbsLevel);
+      sqlite3_bind_int(pChomp, 4, iIdx);
+      sqlite3_step(pChomp);
+      rc = sqlite3_reset(pChomp);
+    }
+  }
+
+  sqlite3_free(root.a);
+  sqlite3_free(block.a);
+  return rc;
+}
+
+/*
+** This function is called after an incrmental-merge operation has run to
+** merge (or partially merge) two or more segments from absolute level
+** iAbsLevel.
+**
+** Each input segment is either removed from the db completely (if all of
+** its data was copied to the output segment by the incrmerge operation)
+** or modified in place so that it no longer contains those entries that
+** have been duplicated in the output segment.
+*/
+static int fts3IncrmergeChomp(
+  Fts3Table *p,                   /* FTS table handle */
+  sqlite3_int64 iAbsLevel,        /* Absolute level containing segments */
+  Fts3MultiSegReader *pCsr,       /* Chomp all segments opened by this cursor */
+  int *pnRem                      /* Number of segments not deleted */
+){
+  int i;
+  int nRem = 0;
+  int rc = SQLITE_OK;
+
+  for(i=pCsr->nSegment-1; i>=0 && rc==SQLITE_OK; i--){
+    Fts3SegReader *pSeg = 0;
+    int j;
+
+    /* Find the Fts3SegReader object with Fts3SegReader.iIdx==i. It is hiding
+    ** somewhere in the pCsr->apSegment[] array.  */
+    for(j=0; ALWAYS(j<pCsr->nSegment); j++){
+      pSeg = pCsr->apSegment[j];
+      if( pSeg->iIdx==i ) break;
+    }
+    assert( j<pCsr->nSegment && pSeg->iIdx==i );
+
+    if( pSeg->aNode==0 ){
+      /* Seg-reader is at EOF. Remove the entire input segment. */
+      rc = fts3DeleteSegment(p, pSeg);
+      if( rc==SQLITE_OK ){
+        rc = fts3RemoveSegdirEntry(p, iAbsLevel, pSeg->iIdx);
+      }
+      *pnRem = 0;
+    }else{
+      /* The incremental merge did not copy all the data from this 
+      ** segment to the upper level. The segment is modified in place
+      ** so that it contains no keys smaller than zTerm/nTerm. */ 
+      const char *zTerm = pSeg->zTerm;
+      int nTerm = pSeg->nTerm;
+      rc = fts3TruncateSegment(p, iAbsLevel, pSeg->iIdx, zTerm, nTerm);
+      nRem++;
+    }
+  }
+
+  if( rc==SQLITE_OK && nRem!=pCsr->nSegment ){
+    rc = fts3RepackSegdirLevel(p, iAbsLevel);
+  }
+
+  *pnRem = nRem;
+  return rc;
+}
+
+/*
+** Store an incr-merge hint in the database.
+*/
+static int fts3IncrmergeHintStore(Fts3Table *p, Blob *pHint){
+  sqlite3_stmt *pReplace = 0;
+  int rc;                         /* Return code */
+
+  rc = fts3SqlStmt(p, SQL_REPLACE_STAT, &pReplace, 0);
+  if( rc==SQLITE_OK ){
+    sqlite3_bind_int(pReplace, 1, FTS_STAT_INCRMERGEHINT);
+    sqlite3_bind_blob(pReplace, 2, pHint->a, pHint->n, SQLITE_STATIC);
+    sqlite3_step(pReplace);
+    rc = sqlite3_reset(pReplace);
+  }
+
+  return rc;
+}
+
+/*
+** Load an incr-merge hint from the database. The incr-merge hint, if one 
+** exists, is stored in the rowid==1 row of the %_stat table.
+**
+** If successful, populate blob *pHint with the value read from the %_stat
+** table and return SQLITE_OK. Otherwise, if an error occurs, return an
+** SQLite error code.
+*/
+static int fts3IncrmergeHintLoad(Fts3Table *p, Blob *pHint){
+  sqlite3_stmt *pSelect = 0;
+  int rc;
+
+  pHint->n = 0;
+  rc = fts3SqlStmt(p, SQL_SELECT_STAT, &pSelect, 0);
+  if( rc==SQLITE_OK ){
+    int rc2;
+    sqlite3_bind_int(pSelect, 1, FTS_STAT_INCRMERGEHINT);
+    if( SQLITE_ROW==sqlite3_step(pSelect) ){
+      const char *aHint = sqlite3_column_blob(pSelect, 0);
+      int nHint = sqlite3_column_bytes(pSelect, 0);
+      if( aHint ){
+        blobGrowBuffer(pHint, nHint, &rc);
+        if( rc==SQLITE_OK ){
+          memcpy(pHint->a, aHint, nHint);
+          pHint->n = nHint;
+        }
+      }
+    }
+    rc2 = sqlite3_reset(pSelect);
+    if( rc==SQLITE_OK ) rc = rc2;
+  }
+
+  return rc;
+}
+
+/*
+** If *pRc is not SQLITE_OK when this function is called, it is a no-op.
+** Otherwise, append an entry to the hint stored in blob *pHint. Each entry
+** consists of two varints, the absolute level number of the input segments 
+** and the number of input segments.
+**
+** If successful, leave *pRc set to SQLITE_OK and return. If an error occurs,
+** set *pRc to an SQLite error code before returning.
+*/
+static void fts3IncrmergeHintPush(
+  Blob *pHint,                    /* Hint blob to append to */
+  i64 iAbsLevel,                  /* First varint to store in hint */
+  int nInput,                     /* Second varint to store in hint */
+  int *pRc                        /* IN/OUT: Error code */
+){
+  blobGrowBuffer(pHint, pHint->n + 2*FTS3_VARINT_MAX, pRc);
+  if( *pRc==SQLITE_OK ){
+    pHint->n += sqlite3Fts3PutVarint(&pHint->a[pHint->n], iAbsLevel);
+    pHint->n += sqlite3Fts3PutVarint(&pHint->a[pHint->n], (i64)nInput);
+  }
+}
+
+/*
+** Read the last entry (most recently pushed) from the hint blob *pHint
+** and then remove the entry. Write the two values read to *piAbsLevel and 
+** *pnInput before returning.
+**
+** If no error occurs, return SQLITE_OK. If the hint blob in *pHint does
+** not contain at least two valid varints, return SQLITE_CORRUPT_VTAB.
+*/
+static int fts3IncrmergeHintPop(Blob *pHint, i64 *piAbsLevel, int *pnInput){
+  const int nHint = pHint->n;
+  int i;
+
+  i = pHint->n-2;
+  while( i>0 && (pHint->a[i-1] & 0x80) ) i--;
+  while( i>0 && (pHint->a[i-1] & 0x80) ) i--;
+
+  pHint->n = i;
+  i += sqlite3Fts3GetVarint(&pHint->a[i], piAbsLevel);
+  i += fts3GetVarint32(&pHint->a[i], pnInput);
+  if( i!=nHint ) return FTS_CORRUPT_VTAB;
+
+  return SQLITE_OK;
+}
+
+
+/*
+** Attempt an incremental merge that writes nMerge leaf blocks.
+**
+** Incremental merges happen nMin segments at a time. The segments 
+** to be merged are the nMin oldest segments (the ones with the smallest 
+** values for the _segdir.idx field) in the highest level that contains 
+** at least nMin segments. Multiple merges might occur in an attempt to 
+** write the quota of nMerge leaf blocks.
+*/
+int sqlite3Fts3Incrmerge(Fts3Table *p, int nMerge, int nMin){
+  int rc;                         /* Return code */
+  int nRem = nMerge;              /* Number of leaf pages yet to  be written */
+  Fts3MultiSegReader *pCsr;       /* Cursor used to read input data */
+  Fts3SegFilter *pFilter;         /* Filter used with cursor pCsr */
+  IncrmergeWriter *pWriter;       /* Writer object */
+  int nSeg = 0;                   /* Number of input segments */
+  sqlite3_int64 iAbsLevel = 0;    /* Absolute level number to work on */
+  Blob hint = {0, 0, 0};          /* Hint read from %_stat table */
+  int bDirtyHint = 0;             /* True if blob 'hint' has been modified */
+
+  /* Allocate space for the cursor, filter and writer objects */
+  const int nAlloc = sizeof(*pCsr) + sizeof(*pFilter) + sizeof(*pWriter);
+  pWriter = (IncrmergeWriter *)sqlite3_malloc(nAlloc);
+  if( !pWriter ) return SQLITE_NOMEM;
+  pFilter = (Fts3SegFilter *)&pWriter[1];
+  pCsr = (Fts3MultiSegReader *)&pFilter[1];
+
+  rc = fts3IncrmergeHintLoad(p, &hint);
+  while( rc==SQLITE_OK && nRem>0 ){
+    const i64 nMod = FTS3_SEGDIR_MAXLEVEL * p->nIndex;
+    sqlite3_stmt *pFindLevel = 0; /* SQL used to determine iAbsLevel */
+    int bUseHint = 0;             /* True if attempting to append */
+    int iIdx = 0;                 /* Largest idx in level (iAbsLevel+1) */
+
+    /* Search the %_segdir table for the absolute level with the smallest
+    ** relative level number that contains at least nMin segments, if any.
+    ** If one is found, set iAbsLevel to the absolute level number and
+    ** nSeg to nMin. If no level with at least nMin segments can be found, 
+    ** set nSeg to -1.
+    */
+    rc = fts3SqlStmt(p, SQL_FIND_MERGE_LEVEL, &pFindLevel, 0);
+    sqlite3_bind_int(pFindLevel, 1, MAX(2, nMin));
+    if( sqlite3_step(pFindLevel)==SQLITE_ROW ){
+      iAbsLevel = sqlite3_column_int64(pFindLevel, 0);
+      nSeg = sqlite3_column_int(pFindLevel, 1);
+      assert( nSeg>=2 );
+    }else{
+      nSeg = -1;
+    }
+    rc = sqlite3_reset(pFindLevel);
+
+    /* If the hint read from the %_stat table is not empty, check if the
+    ** last entry in it specifies a relative level smaller than or equal
+    ** to the level identified by the block above (if any). If so, this 
+    ** iteration of the loop will work on merging at the hinted level.
+    */
+    if( rc==SQLITE_OK && hint.n ){
+      int nHint = hint.n;
+      sqlite3_int64 iHintAbsLevel = 0;      /* Hint level */
+      int nHintSeg = 0;                     /* Hint number of segments */
+
+      rc = fts3IncrmergeHintPop(&hint, &iHintAbsLevel, &nHintSeg);
+      if( nSeg<0 || (iAbsLevel % nMod) >= (iHintAbsLevel % nMod) ){
+        iAbsLevel = iHintAbsLevel;
+        nSeg = nHintSeg;
+        bUseHint = 1;
+        bDirtyHint = 1;
+      }else{
+        /* This undoes the effect of the HintPop() above - so that no entry
+        ** is removed from the hint blob.  */
+        hint.n = nHint;
+      }
+    }
+
+    /* If nSeg is less that zero, then there is no level with at least
+    ** nMin segments and no hint in the %_stat table. No work to do.
+    ** Exit early in this case.  */
+    if( nSeg<0 ) break;
+
+    /* Open a cursor to iterate through the contents of the oldest nSeg 
+    ** indexes of absolute level iAbsLevel. If this cursor is opened using 
+    ** the 'hint' parameters, it is possible that there are less than nSeg
+    ** segments available in level iAbsLevel. In this case, no work is
+    ** done on iAbsLevel - fall through to the next iteration of the loop 
+    ** to start work on some other level.  */
+    memset(pWriter, 0, nAlloc);
+    pFilter->flags = FTS3_SEGMENT_REQUIRE_POS;
+
+    if( rc==SQLITE_OK ){
+      rc = fts3IncrmergeOutputIdx(p, iAbsLevel, &iIdx);
+      assert( bUseHint==1 || bUseHint==0 );
+      if( iIdx==0 || (bUseHint && iIdx==1) ){
+        int bIgnore = 0;
+        rc = fts3SegmentIsMaxLevel(p, iAbsLevel+1, &bIgnore);
+        if( bIgnore ){
+          pFilter->flags |= FTS3_SEGMENT_IGNORE_EMPTY;
+        }
+      }
+    }
+
+    if( rc==SQLITE_OK ){
+      rc = fts3IncrmergeCsr(p, iAbsLevel, nSeg, pCsr);
+    }
+    if( SQLITE_OK==rc && pCsr->nSegment==nSeg
+     && SQLITE_OK==(rc = sqlite3Fts3SegReaderStart(p, pCsr, pFilter))
+     && SQLITE_ROW==(rc = sqlite3Fts3SegReaderStep(p, pCsr))
+    ){
+      if( bUseHint && iIdx>0 ){
+        const char *zKey = pCsr->zTerm;
+        int nKey = pCsr->nTerm;
+        rc = fts3IncrmergeLoad(p, iAbsLevel, iIdx-1, zKey, nKey, pWriter);
+      }else{
+        rc = fts3IncrmergeWriter(p, iAbsLevel, iIdx, pCsr, pWriter);
+      }
+
+      if( rc==SQLITE_OK && pWriter->nLeafEst ){
+        fts3LogMerge(nSeg, iAbsLevel);
+        do {
+          rc = fts3IncrmergeAppend(p, pWriter, pCsr);
+          if( rc==SQLITE_OK ) rc = sqlite3Fts3SegReaderStep(p, pCsr);
+          if( pWriter->nWork>=nRem && rc==SQLITE_ROW ) rc = SQLITE_OK;
+        }while( rc==SQLITE_ROW );
+
+        /* Update or delete the input segments */
+        if( rc==SQLITE_OK ){
+          nRem -= (1 + pWriter->nWork);
+          rc = fts3IncrmergeChomp(p, iAbsLevel, pCsr, &nSeg);
+          if( nSeg!=0 ){
+            bDirtyHint = 1;
+            fts3IncrmergeHintPush(&hint, iAbsLevel, nSeg, &rc);
+          }
+        }
+      }
+
+      if( nSeg!=0 ){
+        pWriter->nLeafData = pWriter->nLeafData * -1;
+      }
+      fts3IncrmergeRelease(p, pWriter, &rc);
+      if( nSeg==0 && pWriter->bNoLeafData==0 ){
+        fts3PromoteSegments(p, iAbsLevel+1, pWriter->nLeafData);
+      }
+    }
+
+    sqlite3Fts3SegReaderFinish(pCsr);
+  }
+
+  /* Write the hint values into the %_stat table for the next incr-merger */
+  if( bDirtyHint && rc==SQLITE_OK ){
+    rc = fts3IncrmergeHintStore(p, &hint);
+  }
+
+  sqlite3_free(pWriter);
+  sqlite3_free(hint.a);
+  return rc;
+}
+
+/*
+** Convert the text beginning at *pz into an integer and return
+** its value.  Advance *pz to point to the first character past
+** the integer.
+*/
+static int fts3Getint(const char **pz){
+  const char *z = *pz;
+  int i = 0;
+  while( (*z)>='0' && (*z)<='9' ) i = 10*i + *(z++) - '0';
+  *pz = z;
+  return i;
+}
+
+/*
+** Process statements of the form:
+**
+**    INSERT INTO table(table) VALUES('merge=A,B');
+**
+** A and B are integers that decode to be the number of leaf pages
+** written for the merge, and the minimum number of segments on a level
+** before it will be selected for a merge, respectively.
+*/
+static int fts3DoIncrmerge(
+  Fts3Table *p,                   /* FTS3 table handle */
+  const char *zParam              /* Nul-terminated string containing "A,B" */
+){
+  int rc;
+  int nMin = (FTS3_MERGE_COUNT / 2);
+  int nMerge = 0;
+  const char *z = zParam;
+
+  /* Read the first integer value */
+  nMerge = fts3Getint(&z);
+
+  /* If the first integer value is followed by a ',',  read the second
+  ** integer value. */
+  if( z[0]==',' && z[1]!='\0' ){
+    z++;
+    nMin = fts3Getint(&z);
+  }
+
+  if( z[0]!='\0' || nMin<2 ){
+    rc = SQLITE_ERROR;
+  }else{
+    rc = SQLITE_OK;
+    if( !p->bHasStat ){
+      assert( p->bFts4==0 );
+      sqlite3Fts3CreateStatTable(&rc, p);
+    }
+    if( rc==SQLITE_OK ){
+      rc = sqlite3Fts3Incrmerge(p, nMerge, nMin);
+    }
+    sqlite3Fts3SegmentsClose(p);
+  }
+  return rc;
+}
+
+/*
+** Process statements of the form:
+**
+**    INSERT INTO table(table) VALUES('automerge=X');
+**
+** where X is an integer.  X==0 means to turn automerge off.  X!=0 means
+** turn it on.  The setting is persistent.
+*/
+static int fts3DoAutoincrmerge(
+  Fts3Table *p,                   /* FTS3 table handle */
+  const char *zParam              /* Nul-terminated string containing boolean */
+){
+  int rc = SQLITE_OK;
+  sqlite3_stmt *pStmt = 0;
+  p->nAutoincrmerge = fts3Getint(&zParam);
+  if( p->nAutoincrmerge==1 || p->nAutoincrmerge>FTS3_MERGE_COUNT ){
+    p->nAutoincrmerge = 8;
+  }
+  if( !p->bHasStat ){
+    assert( p->bFts4==0 );
+    sqlite3Fts3CreateStatTable(&rc, p);
+    if( rc ) return rc;
+  }
+  rc = fts3SqlStmt(p, SQL_REPLACE_STAT, &pStmt, 0);
+  if( rc ) return rc;
+  sqlite3_bind_int(pStmt, 1, FTS_STAT_AUTOINCRMERGE);
+  sqlite3_bind_int(pStmt, 2, p->nAutoincrmerge);
+  sqlite3_step(pStmt);
+  rc = sqlite3_reset(pStmt);
+  return rc;
+}
+
+/*
+** Return a 64-bit checksum for the FTS index entry specified by the
+** arguments to this function.
+*/
+static u64 fts3ChecksumEntry(
+  const char *zTerm,              /* Pointer to buffer containing term */
+  int nTerm,                      /* Size of zTerm in bytes */
+  int iLangid,                    /* Language id for current row */
+  int iIndex,                     /* Index (0..Fts3Table.nIndex-1) */
+  i64 iDocid,                     /* Docid for current row. */
+  int iCol,                       /* Column number */
+  int iPos                        /* Position */
+){
+  int i;
+  u64 ret = (u64)iDocid;
+
+  ret += (ret<<3) + iLangid;
+  ret += (ret<<3) + iIndex;
+  ret += (ret<<3) + iCol;
+  ret += (ret<<3) + iPos;
+  for(i=0; i<nTerm; i++) ret += (ret<<3) + zTerm[i];
+
+  return ret;
+}
+
+/*
+** Return a checksum of all entries in the FTS index that correspond to
+** language id iLangid. The checksum is calculated by XORing the checksums
+** of each individual entry (see fts3ChecksumEntry()) together.
+**
+** If successful, the checksum value is returned and *pRc set to SQLITE_OK.
+** Otherwise, if an error occurs, *pRc is set to an SQLite error code. The
+** return value is undefined in this case.
+*/
+static u64 fts3ChecksumIndex(
+  Fts3Table *p,                   /* FTS3 table handle */
+  int iLangid,                    /* Language id to return cksum for */
+  int iIndex,                     /* Index to cksum (0..p->nIndex-1) */
+  int *pRc                        /* OUT: Return code */
+){
+  Fts3SegFilter filter;
+  Fts3MultiSegReader csr;
+  int rc;
+  u64 cksum = 0;
+
+  assert( *pRc==SQLITE_OK );
+
+  memset(&filter, 0, sizeof(filter));
+  memset(&csr, 0, sizeof(csr));
+  filter.flags =  FTS3_SEGMENT_REQUIRE_POS|FTS3_SEGMENT_IGNORE_EMPTY;
+  filter.flags |= FTS3_SEGMENT_SCAN;
+
+  rc = sqlite3Fts3SegReaderCursor(
+      p, iLangid, iIndex, FTS3_SEGCURSOR_ALL, 0, 0, 0, 1,&csr
+  );
+  if( rc==SQLITE_OK ){
+    rc = sqlite3Fts3SegReaderStart(p, &csr, &filter);
+  }
+
+  if( rc==SQLITE_OK ){
+    while( SQLITE_ROW==(rc = sqlite3Fts3SegReaderStep(p, &csr)) ){
+      char *pCsr = csr.aDoclist;
+      char *pEnd = &pCsr[csr.nDoclist];
+
+      i64 iDocid = 0;
+      i64 iCol = 0;
+      i64 iPos = 0;
+
+      pCsr += sqlite3Fts3GetVarint(pCsr, &iDocid);
+      while( pCsr<pEnd ){
+        i64 iVal = 0;
+        pCsr += sqlite3Fts3GetVarint(pCsr, &iVal);
+        if( pCsr<pEnd ){
+          if( iVal==0 || iVal==1 ){
+            iCol = 0;
+            iPos = 0;
+            if( iVal ){
+              pCsr += sqlite3Fts3GetVarint(pCsr, &iCol);
+            }else{
+              pCsr += sqlite3Fts3GetVarint(pCsr, &iVal);
+              iDocid += iVal;
+            }
+          }else{
+            iPos += (iVal - 2);
+            cksum = cksum ^ fts3ChecksumEntry(
+                csr.zTerm, csr.nTerm, iLangid, iIndex, iDocid,
+                (int)iCol, (int)iPos
+            );
+          }
+        }
+      }
+    }
+  }
+  sqlite3Fts3SegReaderFinish(&csr);
+
+  *pRc = rc;
+  return cksum;
+}
+
+/*
+** Check if the contents of the FTS index match the current contents of the
+** content table. If no error occurs and the contents do match, set *pbOk
+** to true and return SQLITE_OK. Or if the contents do not match, set *pbOk
+** to false before returning.
+**
+** If an error occurs (e.g. an OOM or IO error), return an SQLite error 
+** code. The final value of *pbOk is undefined in this case.
+*/
+static int fts3IntegrityCheck(Fts3Table *p, int *pbOk){
+  int rc = SQLITE_OK;             /* Return code */
+  u64 cksum1 = 0;                 /* Checksum based on FTS index contents */
+  u64 cksum2 = 0;                 /* Checksum based on %_content contents */
+  sqlite3_stmt *pAllLangid = 0;   /* Statement to return all language-ids */
+
+  /* This block calculates the checksum according to the FTS index. */
+  rc = fts3SqlStmt(p, SQL_SELECT_ALL_LANGID, &pAllLangid, 0);
+  if( rc==SQLITE_OK ){
+    int rc2;
+    sqlite3_bind_int(pAllLangid, 1, p->iPrevLangid);
+    sqlite3_bind_int(pAllLangid, 2, p->nIndex);
+    while( rc==SQLITE_OK && sqlite3_step(pAllLangid)==SQLITE_ROW ){
+      int iLangid = sqlite3_column_int(pAllLangid, 0);
+      int i;
+      for(i=0; i<p->nIndex; i++){
+        cksum1 = cksum1 ^ fts3ChecksumIndex(p, iLangid, i, &rc);
+      }
+    }
+    rc2 = sqlite3_reset(pAllLangid);
+    if( rc==SQLITE_OK ) rc = rc2;
+  }
+
+  /* This block calculates the checksum according to the %_content table */
+  if( rc==SQLITE_OK ){
+    sqlite3_tokenizer_module const *pModule = p->pTokenizer->pModule;
+    sqlite3_stmt *pStmt = 0;
+    char *zSql;
+   
+    zSql = sqlite3_mprintf("SELECT %s" , p->zReadExprlist);
+    if( !zSql ){
+      rc = SQLITE_NOMEM;
+    }else{
+      rc = sqlite3_prepare_v2(p->db, zSql, -1, &pStmt, 0);
+      sqlite3_free(zSql);
+    }
+
+    while( rc==SQLITE_OK && SQLITE_ROW==sqlite3_step(pStmt) ){
+      i64 iDocid = sqlite3_column_int64(pStmt, 0);
+      int iLang = langidFromSelect(p, pStmt);
+      int iCol;
+
+      for(iCol=0; rc==SQLITE_OK && iCol<p->nColumn; iCol++){
+        if( p->abNotindexed[iCol]==0 ){
+          const char *zText = (const char *)sqlite3_column_text(pStmt, iCol+1);
+          int nText = sqlite3_column_bytes(pStmt, iCol+1);
+          sqlite3_tokenizer_cursor *pT = 0;
+
+          rc = sqlite3Fts3OpenTokenizer(p->pTokenizer, iLang, zText, nText,&pT);
+          while( rc==SQLITE_OK ){
+            char const *zToken;       /* Buffer containing token */
+            int nToken = 0;           /* Number of bytes in token */
+            int iDum1 = 0, iDum2 = 0; /* Dummy variables */
+            int iPos = 0;             /* Position of token in zText */
+
+            rc = pModule->xNext(pT, &zToken, &nToken, &iDum1, &iDum2, &iPos);
+            if( rc==SQLITE_OK ){
+              int i;
+              cksum2 = cksum2 ^ fts3ChecksumEntry(
+                  zToken, nToken, iLang, 0, iDocid, iCol, iPos
+              );
+              for(i=1; i<p->nIndex; i++){
+                if( p->aIndex[i].nPrefix<=nToken ){
+                  cksum2 = cksum2 ^ fts3ChecksumEntry(
+                      zToken, p->aIndex[i].nPrefix, iLang, i, iDocid, iCol, iPos
+                  );
+                }
+              }
+            }
+          }
+          if( pT ) pModule->xClose(pT);
+          if( rc==SQLITE_DONE ) rc = SQLITE_OK;
+        }
+      }
+    }
+
+    sqlite3_finalize(pStmt);
+  }
+
+  *pbOk = (cksum1==cksum2);
+  return rc;
+}
+
+/*
+** Run the integrity-check. If no error occurs and the current contents of
+** the FTS index are correct, return SQLITE_OK. Or, if the contents of the
+** FTS index are incorrect, return SQLITE_CORRUPT_VTAB.
+**
+** Or, if an error (e.g. an OOM or IO error) occurs, return an SQLite 
+** error code.
+**
+** The integrity-check works as follows. For each token and indexed token
+** prefix in the document set, a 64-bit checksum is calculated (by code
+** in fts3ChecksumEntry()) based on the following:
+**
+**     + The index number (0 for the main index, 1 for the first prefix
+**       index etc.),
+**     + The token (or token prefix) text itself, 
+**     + The language-id of the row it appears in,
+**     + The docid of the row it appears in,
+**     + The column it appears in, and
+**     + The tokens position within that column.
+**
+** The checksums for all entries in the index are XORed together to create
+** a single checksum for the entire index.
+**
+** The integrity-check code calculates the same checksum in two ways:
+**
+**     1. By scanning the contents of the FTS index, and 
+**     2. By scanning and tokenizing the content table.
+**
+** If the two checksums are identical, the integrity-check is deemed to have
+** passed.
+*/
+static int fts3DoIntegrityCheck(
+  Fts3Table *p                    /* FTS3 table handle */
+){
+  int rc;
+  int bOk = 0;
+  rc = fts3IntegrityCheck(p, &bOk);
+  if( rc==SQLITE_OK && bOk==0 ) rc = FTS_CORRUPT_VTAB;
+  return rc;
+}
+
+/*
+** Handle a 'special' INSERT of the form:
+**
+**   "INSERT INTO tbl(tbl) VALUES(<expr>)"
+**
+** Argument pVal contains the result of <expr>. Currently the only 
+** meaningful value to insert is the text 'optimize'.
+*/
+static int fts3SpecialInsert(Fts3Table *p, sqlite3_value *pVal){
+  int rc;                         /* Return Code */
+  const char *zVal = (const char *)sqlite3_value_text(pVal);
+  int nVal = sqlite3_value_bytes(pVal);
+
+  if( !zVal ){
+    return SQLITE_NOMEM;
+  }else if( nVal==8 && 0==sqlite3_strnicmp(zVal, "optimize", 8) ){
+    rc = fts3DoOptimize(p, 0);
+  }else if( nVal==7 && 0==sqlite3_strnicmp(zVal, "rebuild", 7) ){
+    rc = fts3DoRebuild(p);
+  }else if( nVal==15 && 0==sqlite3_strnicmp(zVal, "integrity-check", 15) ){
+    rc = fts3DoIntegrityCheck(p);
+  }else if( nVal>6 && 0==sqlite3_strnicmp(zVal, "merge=", 6) ){
+    rc = fts3DoIncrmerge(p, &zVal[6]);
+  }else if( nVal>10 && 0==sqlite3_strnicmp(zVal, "automerge=", 10) ){
+    rc = fts3DoAutoincrmerge(p, &zVal[10]);
+#ifdef SQLITE_TEST
+  }else if( nVal>9 && 0==sqlite3_strnicmp(zVal, "nodesize=", 9) ){
+    p->nNodeSize = atoi(&zVal[9]);
+    rc = SQLITE_OK;
+  }else if( nVal>11 && 0==sqlite3_strnicmp(zVal, "maxpending=", 9) ){
+    p->nMaxPendingData = atoi(&zVal[11]);
+    rc = SQLITE_OK;
+  }else if( nVal>21 && 0==sqlite3_strnicmp(zVal, "test-no-incr-doclist=", 21) ){
+    p->bNoIncrDoclist = atoi(&zVal[21]);
+    rc = SQLITE_OK;
+#endif
+  }else{
+    rc = SQLITE_ERROR;
+  }
+
+  return rc;
+}
+
+#ifndef SQLITE_DISABLE_FTS4_DEFERRED
+/*
+** Delete all cached deferred doclists. Deferred doclists are cached
+** (allocated) by the sqlite3Fts3CacheDeferredDoclists() function.
+*/
+void sqlite3Fts3FreeDeferredDoclists(Fts3Cursor *pCsr){
+  Fts3DeferredToken *pDef;
+  for(pDef=pCsr->pDeferred; pDef; pDef=pDef->pNext){
+    fts3PendingListDelete(pDef->pList);
+    pDef->pList = 0;
+  }
+}
+
+/*
+** Free all entries in the pCsr->pDeffered list. Entries are added to 
+** this list using sqlite3Fts3DeferToken().
+*/
+void sqlite3Fts3FreeDeferredTokens(Fts3Cursor *pCsr){
+  Fts3DeferredToken *pDef;
+  Fts3DeferredToken *pNext;
+  for(pDef=pCsr->pDeferred; pDef; pDef=pNext){
+    pNext = pDef->pNext;
+    fts3PendingListDelete(pDef->pList);
+    sqlite3_free(pDef);
+  }
+  pCsr->pDeferred = 0;
+}
+
+/*
+** Generate deferred-doclists for all tokens in the pCsr->pDeferred list
+** based on the row that pCsr currently points to.
+**
+** A deferred-doclist is like any other doclist with position information
+** included, except that it only contains entries for a single row of the
+** table, not for all rows.
+*/
+int sqlite3Fts3CacheDeferredDoclists(Fts3Cursor *pCsr){
+  int rc = SQLITE_OK;             /* Return code */
+  if( pCsr->pDeferred ){
+    int i;                        /* Used to iterate through table columns */
+    sqlite3_int64 iDocid;         /* Docid of the row pCsr points to */
+    Fts3DeferredToken *pDef;      /* Used to iterate through deferred tokens */
+  
+    Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
+    sqlite3_tokenizer *pT = p->pTokenizer;
+    sqlite3_tokenizer_module const *pModule = pT->pModule;
+   
+    assert( pCsr->isRequireSeek==0 );
+    iDocid = sqlite3_column_int64(pCsr->pStmt, 0);
+  
+    for(i=0; i<p->nColumn && rc==SQLITE_OK; i++){
+      if( p->abNotindexed[i]==0 ){
+        const char *zText = (const char *)sqlite3_column_text(pCsr->pStmt, i+1);
+        sqlite3_tokenizer_cursor *pTC = 0;
+
+        rc = sqlite3Fts3OpenTokenizer(pT, pCsr->iLangid, zText, -1, &pTC);
+        while( rc==SQLITE_OK ){
+          char const *zToken;       /* Buffer containing token */
+          int nToken = 0;           /* Number of bytes in token */
+          int iDum1 = 0, iDum2 = 0; /* Dummy variables */
+          int iPos = 0;             /* Position of token in zText */
+
+          rc = pModule->xNext(pTC, &zToken, &nToken, &iDum1, &iDum2, &iPos);
+          for(pDef=pCsr->pDeferred; pDef && rc==SQLITE_OK; pDef=pDef->pNext){
+            Fts3PhraseToken *pPT = pDef->pToken;
+            if( (pDef->iCol>=p->nColumn || pDef->iCol==i)
+                && (pPT->bFirst==0 || iPos==0)
+                && (pPT->n==nToken || (pPT->isPrefix && pPT->n<nToken))
+                && (0==memcmp(zToken, pPT->z, pPT->n))
+              ){
+              fts3PendingListAppend(&pDef->pList, iDocid, i, iPos, &rc);
+            }
+          }
+        }
+        if( pTC ) pModule->xClose(pTC);
+        if( rc==SQLITE_DONE ) rc = SQLITE_OK;
+      }
+    }
+
+    for(pDef=pCsr->pDeferred; pDef && rc==SQLITE_OK; pDef=pDef->pNext){
+      if( pDef->pList ){
+        rc = fts3PendingListAppendVarint(&pDef->pList, 0);
+      }
+    }
+  }
+
+  return rc;
+}
+
+int sqlite3Fts3DeferredTokenList(
+  Fts3DeferredToken *p, 
+  char **ppData, 
+  int *pnData
+){
+  char *pRet;
+  int nSkip;
+  sqlite3_int64 dummy;
+
+  *ppData = 0;
+  *pnData = 0;
+
+  if( p->pList==0 ){
+    return SQLITE_OK;
+  }
+
+  pRet = (char *)sqlite3_malloc(p->pList->nData);
+  if( !pRet ) return SQLITE_NOMEM;
+
+  nSkip = sqlite3Fts3GetVarint(p->pList->aData, &dummy);
+  *pnData = p->pList->nData - nSkip;
+  *ppData = pRet;
+  
+  memcpy(pRet, &p->pList->aData[nSkip], *pnData);
+  return SQLITE_OK;
+}
+
+/*
+** Add an entry for token pToken to the pCsr->pDeferred list.
+*/
+int sqlite3Fts3DeferToken(
+  Fts3Cursor *pCsr,               /* Fts3 table cursor */
+  Fts3PhraseToken *pToken,        /* Token to defer */
+  int iCol                        /* Column that token must appear in (or -1) */
+){
+  Fts3DeferredToken *pDeferred;
+  pDeferred = sqlite3_malloc(sizeof(*pDeferred));
+  if( !pDeferred ){
+    return SQLITE_NOMEM;
+  }
+  memset(pDeferred, 0, sizeof(*pDeferred));
+  pDeferred->pToken = pToken;
+  pDeferred->pNext = pCsr->pDeferred; 
+  pDeferred->iCol = iCol;
+  pCsr->pDeferred = pDeferred;
+
+  assert( pToken->pDeferred==0 );
+  pToken->pDeferred = pDeferred;
+
+  return SQLITE_OK;
+}
+#endif
+
+/*
+** SQLite value pRowid contains the rowid of a row that may or may not be
+** present in the FTS3 table. If it is, delete it and adjust the contents
+** of subsiduary data structures accordingly.
+*/
+static int fts3DeleteByRowid(
+  Fts3Table *p, 
+  sqlite3_value *pRowid, 
+  int *pnChng,                    /* IN/OUT: Decrement if row is deleted */
+  u32 *aSzDel
+){
+  int rc = SQLITE_OK;             /* Return code */
+  int bFound = 0;                 /* True if *pRowid really is in the table */
+
+  fts3DeleteTerms(&rc, p, pRowid, aSzDel, &bFound);
+  if( bFound && rc==SQLITE_OK ){
+    int isEmpty = 0;              /* Deleting *pRowid leaves the table empty */
+    rc = fts3IsEmpty(p, pRowid, &isEmpty);
+    if( rc==SQLITE_OK ){
+      if( isEmpty ){
+        /* Deleting this row means the whole table is empty. In this case
+        ** delete the contents of all three tables and throw away any
+        ** data in the pendingTerms hash table.  */
+        rc = fts3DeleteAll(p, 1);
+        *pnChng = 0;
+        memset(aSzDel, 0, sizeof(u32) * (p->nColumn+1) * 2);
+      }else{
+        *pnChng = *pnChng - 1;
+        if( p->zContentTbl==0 ){
+          fts3SqlExec(&rc, p, SQL_DELETE_CONTENT, &pRowid);
+        }
+        if( p->bHasDocsize ){
+          fts3SqlExec(&rc, p, SQL_DELETE_DOCSIZE, &pRowid);
+        }
+      }
+    }
+  }
+
+  return rc;
+}
+
+/*
+** This function does the work for the xUpdate method of FTS3 virtual
+** tables. The schema of the virtual table being:
+**
+**     CREATE TABLE <table name>( 
+**       <user columns>,
+**       <table name> HIDDEN, 
+**       docid HIDDEN, 
+**       <langid> HIDDEN
+**     );
+**
+** 
+*/
+int sqlite3Fts3UpdateMethod(
+  sqlite3_vtab *pVtab,            /* FTS3 vtab object */
+  int nArg,                       /* Size of argument array */
+  sqlite3_value **apVal,          /* Array of arguments */
+  sqlite_int64 *pRowid            /* OUT: The affected (or effected) rowid */
+){
+  Fts3Table *p = (Fts3Table *)pVtab;
+  int rc = SQLITE_OK;             /* Return Code */
+  int isRemove = 0;               /* True for an UPDATE or DELETE */
+  u32 *aSzIns = 0;                /* Sizes of inserted documents */
+  u32 *aSzDel = 0;                /* Sizes of deleted documents */
+  int nChng = 0;                  /* Net change in number of documents */
+  int bInsertDone = 0;
+
+  /* At this point it must be known if the %_stat table exists or not.
+  ** So bHasStat may not be 2.  */
+  assert( p->bHasStat==0 || p->bHasStat==1 );
+
+  assert( p->pSegments==0 );
+  assert( 
+      nArg==1                     /* DELETE operations */
+   || nArg==(2 + p->nColumn + 3)  /* INSERT or UPDATE operations */
+  );
+
+  /* Check for a "special" INSERT operation. One of the form:
+  **
+  **   INSERT INTO xyz(xyz) VALUES('command');
+  */
+  if( nArg>1 
+   && sqlite3_value_type(apVal[0])==SQLITE_NULL 
+   && sqlite3_value_type(apVal[p->nColumn+2])!=SQLITE_NULL 
+  ){
+    rc = fts3SpecialInsert(p, apVal[p->nColumn+2]);
+    goto update_out;
+  }
+
+  if( nArg>1 && sqlite3_value_int(apVal[2 + p->nColumn + 2])<0 ){
+    rc = SQLITE_CONSTRAINT;
+    goto update_out;
+  }
+
+  /* Allocate space to hold the change in document sizes */
+  aSzDel = sqlite3_malloc( sizeof(aSzDel[0])*(p->nColumn+1)*2 );
+  if( aSzDel==0 ){
+    rc = SQLITE_NOMEM;
+    goto update_out;
+  }
+  aSzIns = &aSzDel[p->nColumn+1];
+  memset(aSzDel, 0, sizeof(aSzDel[0])*(p->nColumn+1)*2);
+
+  rc = fts3Writelock(p);
+  if( rc!=SQLITE_OK ) goto update_out;
+
+  /* If this is an INSERT operation, or an UPDATE that modifies the rowid
+  ** value, then this operation requires constraint handling.
+  **
+  ** If the on-conflict mode is REPLACE, this means that the existing row
+  ** should be deleted from the database before inserting the new row. Or,
+  ** if the on-conflict mode is other than REPLACE, then this method must
+  ** detect the conflict and return SQLITE_CONSTRAINT before beginning to
+  ** modify the database file.
+  */
+  if( nArg>1 && p->zContentTbl==0 ){
+    /* Find the value object that holds the new rowid value. */
+    sqlite3_value *pNewRowid = apVal[3+p->nColumn];
+    if( sqlite3_value_type(pNewRowid)==SQLITE_NULL ){
+      pNewRowid = apVal[1];
+    }
+
+    if( sqlite3_value_type(pNewRowid)!=SQLITE_NULL && ( 
+        sqlite3_value_type(apVal[0])==SQLITE_NULL
+     || sqlite3_value_int64(apVal[0])!=sqlite3_value_int64(pNewRowid)
+    )){
+      /* The new rowid is not NULL (in this case the rowid will be
+      ** automatically assigned and there is no chance of a conflict), and 
+      ** the statement is either an INSERT or an UPDATE that modifies the
+      ** rowid column. So if the conflict mode is REPLACE, then delete any
+      ** existing row with rowid=pNewRowid. 
+      **
+      ** Or, if the conflict mode is not REPLACE, insert the new record into 
+      ** the %_content table. If we hit the duplicate rowid constraint (or any
+      ** other error) while doing so, return immediately.
+      **
+      ** This branch may also run if pNewRowid contains a value that cannot
+      ** be losslessly converted to an integer. In this case, the eventual 
+      ** call to fts3InsertData() (either just below or further on in this
+      ** function) will return SQLITE_MISMATCH. If fts3DeleteByRowid is 
+      ** invoked, it will delete zero rows (since no row will have
+      ** docid=$pNewRowid if $pNewRowid is not an integer value).
+      */
+      if( sqlite3_vtab_on_conflict(p->db)==SQLITE_REPLACE ){
+        rc = fts3DeleteByRowid(p, pNewRowid, &nChng, aSzDel);
+      }else{
+        rc = fts3InsertData(p, apVal, pRowid);
+        bInsertDone = 1;
+      }
+    }
+  }
+  if( rc!=SQLITE_OK ){
+    goto update_out;
+  }
+
+  /* If this is a DELETE or UPDATE operation, remove the old record. */
+  if( sqlite3_value_type(apVal[0])!=SQLITE_NULL ){
+    assert( sqlite3_value_type(apVal[0])==SQLITE_INTEGER );
+    rc = fts3DeleteByRowid(p, apVal[0], &nChng, aSzDel);
+    isRemove = 1;
+  }
+  
+  /* If this is an INSERT or UPDATE operation, insert the new record. */
+  if( nArg>1 && rc==SQLITE_OK ){
+    int iLangid = sqlite3_value_int(apVal[2 + p->nColumn + 2]);
+    if( bInsertDone==0 ){
+      rc = fts3InsertData(p, apVal, pRowid);
+      if( rc==SQLITE_CONSTRAINT && p->zContentTbl==0 ){
+        rc = FTS_CORRUPT_VTAB;
+      }
+    }
+    if( rc==SQLITE_OK && (!isRemove || *pRowid!=p->iPrevDocid ) ){
+      rc = fts3PendingTermsDocid(p, 0, iLangid, *pRowid);
+    }
+    if( rc==SQLITE_OK ){
+      assert( p->iPrevDocid==*pRowid );
+      rc = fts3InsertTerms(p, iLangid, apVal, aSzIns);
+    }
+    if( p->bHasDocsize ){
+      fts3InsertDocsize(&rc, p, aSzIns);
+    }
+    nChng++;
+  }
+
+  if( p->bFts4 ){
+    fts3UpdateDocTotals(&rc, p, aSzIns, aSzDel, nChng);
+  }
+
+ update_out:
+  sqlite3_free(aSzDel);
+  sqlite3Fts3SegmentsClose(p);
+  return rc;
+}
+
+/* 
+** Flush any data in the pending-terms hash table to disk. If successful,
+** merge all segments in the database (including the new segment, if 
+** there was any data to flush) into a single segment. 
+*/
+int sqlite3Fts3Optimize(Fts3Table *p){
+  int rc;
+  rc = sqlite3_exec(p->db, "SAVEPOINT fts3", 0, 0, 0);
+  if( rc==SQLITE_OK ){
+    rc = fts3DoOptimize(p, 1);
+    if( rc==SQLITE_OK || rc==SQLITE_DONE ){
+      int rc2 = sqlite3_exec(p->db, "RELEASE fts3", 0, 0, 0);
+      if( rc2!=SQLITE_OK ) rc = rc2;
+    }else{
+      sqlite3_exec(p->db, "ROLLBACK TO fts3", 0, 0, 0);
+      sqlite3_exec(p->db, "RELEASE fts3", 0, 0, 0);
+    }
+  }
+  sqlite3Fts3SegmentsClose(p);
+  return rc;
+}
+
+#endif