Move bundled copy of sqlite one level deeper to better separate it...

third_party/sqlite/src/pager.c

-/*
-** 2001 September 15
-**
-** The author disclaims copyright to this source code.  In place of
-** a legal notice, here is a blessing:
-**
-**    May you do good and not evil.
-**    May you find forgiveness for yourself and forgive others.
-**    May you share freely, never taking more than you give.
-**
-*************************************************************************
-** This is the implementation of the page cache subsystem or "pager".
-** 
-** The pager is used to access a database disk file.  It implements
-** atomic commit and rollback through the use of a journal file that
-** is separate from the database file.  The pager also implements file
-** locking to prevent two processes from writing the same database
-** file simultaneously, or one process from reading the database while
-** another is writing.
-**
-** @(#) $Id: pager.c,v 1.629 2009/08/10 17:48:57 drh Exp $
-*/
-#ifndef SQLITE_OMIT_DISKIO
-#include "sqliteInt.h"
-
-/*
-** Macros for troubleshooting.  Normally turned off
-*/
-#if 0
-int sqlite3PagerTrace=1;  /* True to enable tracing */
-#define sqlite3DebugPrintf printf
-#define PAGERTRACE(X)     if( sqlite3PagerTrace ){ sqlite3DebugPrintf X; }
-#else
-#define PAGERTRACE(X)
-#endif
-
-/*
-** The following two macros are used within the PAGERTRACE() macros above
-** to print out file-descriptors. 
-**
-** PAGERID() takes a pointer to a Pager struct as its argument. The
-** associated file-descriptor is returned. FILEHANDLEID() takes an sqlite3_file
-** struct as its argument.
-*/
-#define PAGERID(p) ((int)(p->fd))
-#define FILEHANDLEID(fd) ((int)fd)
-
-/*
-** The page cache as a whole is always in one of the following
-** states:
-**
-**   PAGER_UNLOCK        The page cache is not currently reading or 
-**                       writing the database file.  There is no
-**                       data held in memory.  This is the initial
-**                       state.
-**
-**   PAGER_SHARED        The page cache is reading the database.
-**                       Writing is not permitted.  There can be
-**                       multiple readers accessing the same database
-**                       file at the same time.
-**
-**   PAGER_RESERVED      This process has reserved the database for writing
-**                       but has not yet made any changes.  Only one process
-**                       at a time can reserve the database.  The original
-**                       database file has not been modified so other
-**                       processes may still be reading the on-disk
-**                       database file.
-**
-**   PAGER_EXCLUSIVE     The page cache is writing the database.
-**                       Access is exclusive.  No other processes or
-**                       threads can be reading or writing while one
-**                       process is writing.
-**
-**   PAGER_SYNCED        The pager moves to this state from PAGER_EXCLUSIVE
-**                       after all dirty pages have been written to the
-**                       database file and the file has been synced to
-**                       disk. All that remains to do is to remove or
-**                       truncate the journal file and the transaction 
-**                       will be committed.
-**
-** The page cache comes up in PAGER_UNLOCK.  The first time a
-** sqlite3PagerGet() occurs, the state transitions to PAGER_SHARED.
-** After all pages have been released using sqlite_page_unref(),
-** the state transitions back to PAGER_UNLOCK.  The first time
-** that sqlite3PagerWrite() is called, the state transitions to
-** PAGER_RESERVED.  (Note that sqlite3PagerWrite() can only be
-** called on an outstanding page which means that the pager must
-** be in PAGER_SHARED before it transitions to PAGER_RESERVED.)
-** PAGER_RESERVED means that there is an open rollback journal.
-** The transition to PAGER_EXCLUSIVE occurs before any changes
-** are made to the database file, though writes to the rollback
-** journal occurs with just PAGER_RESERVED.  After an sqlite3PagerRollback()
-** or sqlite3PagerCommitPhaseTwo(), the state can go back to PAGER_SHARED,
-** or it can stay at PAGER_EXCLUSIVE if we are in exclusive access mode.
-*/
-#define PAGER_UNLOCK      0
-#define PAGER_SHARED      1   /* same as SHARED_LOCK */
-#define PAGER_RESERVED    2   /* same as RESERVED_LOCK */
-#define PAGER_EXCLUSIVE   4   /* same as EXCLUSIVE_LOCK */
-#define PAGER_SYNCED      5
-
-/*
-** A macro used for invoking the codec if there is one
-*/
-#ifdef SQLITE_HAS_CODEC
-# define CODEC1(P,D,N,X,E) \
-    if( P->xCodec && P->xCodec(P->pCodec,D,N,X)==0 ){ E; }
-# define CODEC2(P,D,N,X,E,O) \
-    if( P->xCodec==0 ){ O=(char*)D; }else \
-    if( (O=(char*)(P->xCodec(P->pCodec,D,N,X)))==0 ){ E; }
-#else
-# define CODEC1(P,D,N,X,E)   /* NO-OP */
-# define CODEC2(P,D,N,X,E,O) O=(char*)D
-#endif
-
-/*
-** The maximum allowed sector size. 64KiB. If the xSectorsize() method 
-** returns a value larger than this, then MAX_SECTOR_SIZE is used instead.
-** This could conceivably cause corruption following a power failure on
-** such a system. This is currently an undocumented limit.
-*/
-#define MAX_SECTOR_SIZE 0x10000
-
-/*
-** An instance of the following structure is allocated for each active
-** savepoint and statement transaction in the system. All such structures
-** are stored in the Pager.aSavepoint[] array, which is allocated and
-** resized using sqlite3Realloc().
-**
-** When a savepoint is created, the PagerSavepoint.iHdrOffset field is
-** set to 0. If a journal-header is written into the main journal while
-** the savepoint is active, then iHdrOffset is set to the byte offset 
-** immediately following the last journal record written into the main
-** journal before the journal-header. This is required during savepoint
-** rollback (see pagerPlaybackSavepoint()).
-*/
-typedef struct PagerSavepoint PagerSavepoint;
-struct PagerSavepoint {
-  i64 iOffset;                 /* Starting offset in main journal */
-  i64 iHdrOffset;              /* See above */
-  Bitvec *pInSavepoint;        /* Set of pages in this savepoint */
-  Pgno nOrig;                  /* Original number of pages in file */
-  Pgno iSubRec;                /* Index of first record in sub-journal */
-};
-
-/*
-** A open page cache is an instance of the following structure.
-**
-** errCode
-**
-**   Pager.errCode may be set to SQLITE_IOERR, SQLITE_CORRUPT, or
-**   or SQLITE_FULL. Once one of the first three errors occurs, it persists
-**   and is returned as the result of every major pager API call.  The
-**   SQLITE_FULL return code is slightly different. It persists only until the
-**   next successful rollback is performed on the pager cache. Also,
-**   SQLITE_FULL does not affect the sqlite3PagerGet() and sqlite3PagerLookup()
-**   APIs, they may still be used successfully.
-**
-** dbSizeValid, dbSize, dbOrigSize, dbFileSize
-**
-**   Managing the size of the database file in pages is a little complicated.
-**   The variable Pager.dbSize contains the number of pages that the database
-**   image currently contains. As the database image grows or shrinks this
-**   variable is updated. The variable Pager.dbFileSize contains the number
-**   of pages in the database file. This may be different from Pager.dbSize
-**   if some pages have been appended to the database image but not yet written
-**   out from the cache to the actual file on disk. Or if the image has been
-**   truncated by an incremental-vacuum operation. The Pager.dbOrigSize variable
-**   contains the number of pages in the database image when the current
-**   transaction was opened. The contents of all three of these variables is
-**   only guaranteed to be correct if the boolean Pager.dbSizeValid is true.
-**
-**   TODO: Under what conditions is dbSizeValid set? Cleared?
-**
-** changeCountDone
-**
-**   This boolean variable is used to make sure that the change-counter 
-**   (the 4-byte header field at byte offset 24 of the database file) is 
-**   not updated more often than necessary. 
-**
-**   It is set to true when the change-counter field is updated, which 
-**   can only happen if an exclusive lock is held on the database file.
-**   It is cleared (set to false) whenever an exclusive lock is 
-**   relinquished on the database file. Each time a transaction is committed,
-**   The changeCountDone flag is inspected. If it is true, the work of
-**   updating the change-counter is omitted for the current transaction.
-**
-**   This mechanism means that when running in exclusive mode, a connection 
-**   need only update the change-counter once, for the first transaction
-**   committed.
-**
-** dbModified
-**
-**   The dbModified flag is set whenever a database page is dirtied.
-**   It is cleared at the end of each transaction.
-**
-**   It is used when committing or otherwise ending a transaction. If
-**   the dbModified flag is clear then less work has to be done.
-**
-** journalStarted
-**
-**   This flag is set whenever the the main journal is synced. 
-**
-**   The point of this flag is that it must be set after the 
-**   first journal header in a journal file has been synced to disk.
-**   After this has happened, new pages appended to the database 
-**   do not need the PGHDR_NEED_SYNC flag set, as they do not need
-**   to wait for a journal sync before they can be written out to
-**   the database file (see function pager_write()).
-**   
-** setMaster
-**
-**   This variable is used to ensure that the master journal file name
-**   (if any) is only written into the journal file once.
-**
-**   When committing a transaction, the master journal file name (if any)
-**   may be written into the journal file while the pager is still in
-**   PAGER_RESERVED state (see CommitPhaseOne() for the action). It
-**   then attempts to upgrade to an exclusive lock. If this attempt
-**   fails, then SQLITE_BUSY may be returned to the user and the user
-**   may attempt to commit the transaction again later (calling
-**   CommitPhaseOne() again). This flag is used to ensure that the 
-**   master journal name is only written to the journal file the first
-**   time CommitPhaseOne() is called.
-**
-** doNotSync
-**
-**   This variable is set and cleared by sqlite3PagerWrite().
-**
-** needSync
-**
-**   TODO: It might be easier to set this variable in writeJournalHdr()
-**   and writeMasterJournal() only. Change its meaning to "unsynced data
-**   has been written to the journal".
-**
-** subjInMemory
-**
-**   This is a boolean variable. If true, then any required sub-journal
-**   is opened as an in-memory journal file. If false, then in-memory
-**   sub-journals are only used for in-memory pager files.
-*/
-struct Pager {
-  sqlite3_vfs *pVfs;          /* OS functions to use for IO */
-  u8 exclusiveMode;           /* Boolean. True if locking_mode==EXCLUSIVE */
-  u8 journalMode;             /* On of the PAGER_JOURNALMODE_* values */
-  u8 useJournal;              /* Use a rollback journal on this file */
-  u8 noReadlock;              /* Do not bother to obtain readlocks */
-  u8 noSync;                  /* Do not sync the journal if true */
-  u8 fullSync;                /* Do extra syncs of the journal for robustness */
-  u8 sync_flags;              /* One of SYNC_NORMAL or SYNC_FULL */
-  u8 tempFile;                /* zFilename is a temporary file */
-  u8 readOnly;                /* True for a read-only database */
-  u8 memDb;                   /* True to inhibit all file I/O */
-
-  /* The following block contains those class members that are dynamically
-  ** modified during normal operations. The other variables in this structure
-  ** are either constant throughout the lifetime of the pager, or else
-  ** used to store configuration parameters that affect the way the pager 
-  ** operates.
-  **
-  ** The 'state' variable is described in more detail along with the
-  ** descriptions of the values it may take - PAGER_UNLOCK etc. Many of the
-  ** other variables in this block are described in the comment directly 
-  ** above this class definition.
-  */
-  u8 state;                   /* PAGER_UNLOCK, _SHARED, _RESERVED, etc. */
-  u8 dbModified;              /* True if there are any changes to the Db */
-  u8 needSync;                /* True if an fsync() is needed on the journal */
-  u8 journalStarted;          /* True if header of journal is synced */
-  u8 changeCountDone;         /* Set after incrementing the change-counter */
-  u8 setMaster;               /* True if a m-j name has been written to jrnl */
-  u8 doNotSync;               /* Boolean. While true, do not spill the cache */
-  u8 dbSizeValid;             /* Set when dbSize is correct */
-  u8 subjInMemory;            /* True to use in-memory sub-journals */
-  Pgno dbSize;                /* Number of pages in the database */
-  Pgno dbOrigSize;            /* dbSize before the current transaction */
-  Pgno dbFileSize;            /* Number of pages in the database file */
-  int errCode;                /* One of several kinds of errors */
-  int nRec;                   /* Pages journalled since last j-header written */
-  u32 cksumInit;              /* Quasi-random value added to every checksum */
-  u32 nSubRec;                /* Number of records written to sub-journal */
-  Bitvec *pInJournal;         /* One bit for each page in the database file */
-  sqlite3_file *fd;           /* File descriptor for database */
-  sqlite3_file *jfd;          /* File descriptor for main journal */
-  sqlite3_file *sjfd;         /* File descriptor for sub-journal */
-  i64 journalOff;             /* Current write offset in the journal file */
-  i64 journalHdr;             /* Byte offset to previous journal header */
-  PagerSavepoint *aSavepoint; /* Array of active savepoints */
-  int nSavepoint;             /* Number of elements in aSavepoint[] */
-  char dbFileVers[16];        /* Changes whenever database file changes */
-  u32 sectorSize;             /* Assumed sector size during rollback */
-
-  u16 nExtra;                 /* Add this many bytes to each in-memory page */
-  i16 nReserve;               /* Number of unused bytes at end of each page */
-  u32 vfsFlags;               /* Flags for sqlite3_vfs.xOpen() */
-  int pageSize;               /* Number of bytes in a page */
-  Pgno mxPgno;                /* Maximum allowed size of the database */
-  char *zFilename;            /* Name of the database file */
-  char *zJournal;             /* Name of the journal file */
-  int (*xBusyHandler)(void*); /* Function to call when busy */
-  void *pBusyHandlerArg;      /* Context argument for xBusyHandler */
-#ifdef SQLITE_TEST
-  int nHit, nMiss;            /* Cache hits and missing */
-  int nRead, nWrite;          /* Database pages read/written */
-#endif
-  void (*xReiniter)(DbPage*); /* Call this routine when reloading pages */
-#ifdef SQLITE_HAS_CODEC
-  void *(*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
-  void (*xCodecSizeChng)(void*,int,int); /* Notify of page size changes */
-  void (*xCodecFree)(void*);             /* Destructor for the codec */
-  void *pCodec;               /* First argument to xCodec... methods */
-#endif
-  char *pTmpSpace;            /* Pager.pageSize bytes of space for tmp use */
-  i64 journalSizeLimit;       /* Size limit for persistent journal files */
-  PCache *pPCache;            /* Pointer to page cache object */
-  sqlite3_backup *pBackup;    /* Pointer to list of ongoing backup processes */
-};
-
-/*
-** The following global variables hold counters used for
-** testing purposes only.  These variables do not exist in
-** a non-testing build.  These variables are not thread-safe.
-*/
-#ifdef SQLITE_TEST
-int sqlite3_pager_readdb_count = 0;    /* Number of full pages read from DB */
-int sqlite3_pager_writedb_count = 0;   /* Number of full pages written to DB */
-int sqlite3_pager_writej_count = 0;    /* Number of pages written to journal */
-# define PAGER_INCR(v)  v++
-#else
-# define PAGER_INCR(v)
-#endif
-
-
-
-/*
-** Journal files begin with the following magic string.  The data
-** was obtained from /dev/random.  It is used only as a sanity check.
-**
-** Since version 2.8.0, the journal format contains additional sanity
-** checking information.  If the power fails while the journal is being
-** written, semi-random garbage data might appear in the journal
-** file after power is restored.  If an attempt is then made
-** to roll the journal back, the database could be corrupted.  The additional
-** sanity checking data is an attempt to discover the garbage in the
-** journal and ignore it.
-**
-** The sanity checking information for the new journal format consists
-** of a 32-bit checksum on each page of data.  The checksum covers both
-** the page number and the pPager->pageSize bytes of data for the page.
-** This cksum is initialized to a 32-bit random value that appears in the
-** journal file right after the header.  The random initializer is important,
-** because garbage data that appears at the end of a journal is likely
-** data that was once in other files that have now been deleted.  If the
-** garbage data came from an obsolete journal file, the checksums might
-** be correct.  But by initializing the checksum to random value which
-** is different for every journal, we minimize that risk.
-*/
-static const unsigned char aJournalMagic[] = {
-  0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7,
-};
-
-/*
-** The size of the of each page record in the journal is given by
-** the following macro.
-*/
-#define JOURNAL_PG_SZ(pPager)  ((pPager->pageSize) + 8)
-
-/*
-** The journal header size for this pager. This is usually the same 
-** size as a single disk sector. See also setSectorSize().
-*/
-#define JOURNAL_HDR_SZ(pPager) (pPager->sectorSize)
-
-/*
-** The macro MEMDB is true if we are dealing with an in-memory database.
-** We do this as a macro so that if the SQLITE_OMIT_MEMORYDB macro is set,
-** the value of MEMDB will be a constant and the compiler will optimize
-** out code that would never execute.
-*/
-#ifdef SQLITE_OMIT_MEMORYDB
-# define MEMDB 0
-#else
-# define MEMDB pPager->memDb
-#endif
-
-/*
-** The maximum legal page number is (2^31 - 1).
-*/
-#define PAGER_MAX_PGNO 2147483647
-
-/* Begin preload-cache.patch for Chromium */
-/* See comments above the definition. */
-int sqlite3PagerAcquire2(
-  Pager *pPager,
-  Pgno pgno,
-  DbPage **ppPage,
-  int noContent,
-  unsigned char *pDataToFill);
-/* End preload-cache.patch for Chromium */
-
-#ifndef NDEBUG 
-/*
-** Usage:
-**
-**   assert( assert_pager_state(pPager) );
-*/
-static int assert_pager_state(Pager *pPager){
-
-  /* A temp-file is always in PAGER_EXCLUSIVE or PAGER_SYNCED state. */
-  assert( pPager->tempFile==0 || pPager->state>=PAGER_EXCLUSIVE );
-
-  /* The changeCountDone flag is always set for temp-files */
-  assert( pPager->tempFile==0 || pPager->changeCountDone );
-
-  return 1;
-}
-#endif
-
-/*
-** Return true if it is necessary to write page *pPg into the sub-journal.
-** A page needs to be written into the sub-journal if there exists one
-** or more open savepoints for which:
-**
-**   * The page-number is less than or equal to PagerSavepoint.nOrig, and
-**   * The bit corresponding to the page-number is not set in
-**     PagerSavepoint.pInSavepoint.
-*/
-static int subjRequiresPage(PgHdr *pPg){
-  Pgno pgno = pPg->pgno;
-  Pager *pPager = pPg->pPager;
-  int i;
-  for(i=0; i<pPager->nSavepoint; i++){
-    PagerSavepoint *p = &pPager->aSavepoint[i];
-    if( p->nOrig>=pgno && 0==sqlite3BitvecTest(p->pInSavepoint, pgno) ){
-      return 1;
-    }
-  }
-  return 0;
-}
-
-/*
-** Return true if the page is already in the journal file.
-*/
-static int pageInJournal(PgHdr *pPg){
-  return sqlite3BitvecTest(pPg->pPager->pInJournal, pPg->pgno);
-}
-
-/*
-** Read a 32-bit integer from the given file descriptor.  Store the integer
-** that is read in *pRes.  Return SQLITE_OK if everything worked, or an
-** error code is something goes wrong.
-**
-** All values are stored on disk as big-endian.
-*/
-static int read32bits(sqlite3_file *fd, i64 offset, u32 *pRes){
-  unsigned char ac[4];
-  int rc = sqlite3OsRead(fd, ac, sizeof(ac), offset);
-  if( rc==SQLITE_OK ){
-    *pRes = sqlite3Get4byte(ac);
-  }
-  return rc;
-}
-
-/*
-** Write a 32-bit integer into a string buffer in big-endian byte order.
-*/
-#define put32bits(A,B)  sqlite3Put4byte((u8*)A,B)
-
-/*
-** Write a 32-bit integer into the given file descriptor.  Return SQLITE_OK
-** on success or an error code is something goes wrong.
-*/
-static int write32bits(sqlite3_file *fd, i64 offset, u32 val){
-  char ac[4];
-  put32bits(ac, val);
-  return sqlite3OsWrite(fd, ac, 4, offset);
-}
-
-/*
-** The argument to this macro is a file descriptor (type sqlite3_file*).
-** Return 0 if it is not open, or non-zero (but not 1) if it is.
-**
-** This is so that expressions can be written as:
-**
-**   if( isOpen(pPager->jfd) ){ ...
-**
-** instead of
-**
-**   if( pPager->jfd->pMethods ){ ...
-*/
-#define isOpen(pFd) ((pFd)->pMethods)
-
-/*
-** If file pFd is open, call sqlite3OsUnlock() on it.
-*/
-static int osUnlock(sqlite3_file *pFd, int eLock){
-  if( !isOpen(pFd) ){
-    return SQLITE_OK;
-  }
-  return sqlite3OsUnlock(pFd, eLock);
-}
-
-/*
-** This function determines whether or not the atomic-write optimization
-** can be used with this pager. The optimization can be used if:
-**
-**  (a) the value returned by OsDeviceCharacteristics() indicates that
-**      a database page may be written atomically, and
-**  (b) the value returned by OsSectorSize() is less than or equal
-**      to the page size.
-**
-** The optimization is also always enabled for temporary files. It is
-** an error to call this function if pPager is opened on an in-memory
-** database.
-**
-** If the optimization cannot be used, 0 is returned. If it can be used,
-** then the value returned is the size of the journal file when it
-** contains rollback data for exactly one page.
-*/
-#ifdef SQLITE_ENABLE_ATOMIC_WRITE
-static int jrnlBufferSize(Pager *pPager){
-  assert( !MEMDB );
-  if( !pPager->tempFile ){
-    int dc;                           /* Device characteristics */
-    int nSector;                      /* Sector size */
-    int szPage;                       /* Page size */
-
-    assert( isOpen(pPager->fd) );
-    dc = sqlite3OsDeviceCharacteristics(pPager->fd);
-    nSector = pPager->sectorSize;
-    szPage = pPager->pageSize;
-
-    assert(SQLITE_IOCAP_ATOMIC512==(512>>8));
-    assert(SQLITE_IOCAP_ATOMIC64K==(65536>>8));
-    if( 0==(dc&(SQLITE_IOCAP_ATOMIC|(szPage>>8)) || nSector>szPage) ){
-      return 0;
-    }
-  }
-
-  return JOURNAL_HDR_SZ(pPager) + JOURNAL_PG_SZ(pPager);
-}
-#endif
-
-/*
-** If SQLITE_CHECK_PAGES is defined then we do some sanity checking
-** on the cache using a hash function.  This is used for testing
-** and debugging only.
-*/
-#ifdef SQLITE_CHECK_PAGES
-/*
-** Return a 32-bit hash of the page data for pPage.
-*/
-static u32 pager_datahash(int nByte, unsigned char *pData){
-  u32 hash = 0;
-  int i;
-  for(i=0; i<nByte; i++){
-    hash = (hash*1039) + pData[i];
-  }
-  return hash;
-}
-static u32 pager_pagehash(PgHdr *pPage){
-  return pager_datahash(pPage->pPager->pageSize, (unsigned char *)pPage->pData);
-}
-static void pager_set_pagehash(PgHdr *pPage){
-  pPage->pageHash = pager_pagehash(pPage);
-}
-
-/*
-** The CHECK_PAGE macro takes a PgHdr* as an argument. If SQLITE_CHECK_PAGES
-** is defined, and NDEBUG is not defined, an assert() statement checks
-** that the page is either dirty or still matches the calculated page-hash.
-*/
-#define CHECK_PAGE(x) checkPage(x)
-static void checkPage(PgHdr *pPg){
-  Pager *pPager = pPg->pPager;
-  assert( !pPg->pageHash || pPager->errCode
-      || (pPg->flags&PGHDR_DIRTY) || pPg->pageHash==pager_pagehash(pPg) );
-}
-
-#else
-#define pager_datahash(X,Y)  0
-#define pager_pagehash(X)  0
-#define CHECK_PAGE(x)
-#endif  /* SQLITE_CHECK_PAGES */
-
-/*
-** When this is called the journal file for pager pPager must be open.
-** This function attempts to read a master journal file name from the 
-** end of the file and, if successful, copies it into memory supplied 
-** by the caller. See comments above writeMasterJournal() for the format
-** used to store a master journal file name at the end of a journal file.
-**
-** zMaster must point to a buffer of at least nMaster bytes allocated by
-** the caller. This should be sqlite3_vfs.mxPathname+1 (to ensure there is
-** enough space to write the master journal name). If the master journal
-** name in the journal is longer than nMaster bytes (including a
-** nul-terminator), then this is handled as if no master journal name
-** were present in the journal.
-**
-** If a master journal file name is present at the end of the journal
-** file, then it is copied into the buffer pointed to by zMaster. A
-** nul-terminator byte is appended to the buffer following the master
-** journal file name.
-**
-** If it is determined that no master journal file name is present 
-** zMaster[0] is set to 0 and SQLITE_OK returned.
-**
-** If an error occurs while reading from the journal file, an SQLite
-** error code is returned.
-*/
-static int readMasterJournal(sqlite3_file *pJrnl, char *zMaster, u32 nMaster){
-  int rc;                    /* Return code */
-  u32 len;                   /* Length in bytes of master journal name */
-  i64 szJ;                   /* Total size in bytes of journal file pJrnl */
-  u32 cksum;                 /* MJ checksum value read from journal */
-  u32 u;                     /* Unsigned loop counter */
-  unsigned char aMagic[8];   /* A buffer to hold the magic header */
-  zMaster[0] = '\0';
-
-  if( SQLITE_OK!=(rc = sqlite3OsFileSize(pJrnl, &szJ))
-   || szJ<16
-   || SQLITE_OK!=(rc = read32bits(pJrnl, szJ-16, &len))
-   || len>=nMaster 
-   || SQLITE_OK!=(rc = read32bits(pJrnl, szJ-12, &cksum))
-   || SQLITE_OK!=(rc = sqlite3OsRead(pJrnl, aMagic, 8, szJ-8))
-   || memcmp(aMagic, aJournalMagic, 8)
-   || SQLITE_OK!=(rc = sqlite3OsRead(pJrnl, zMaster, len, szJ-16-len))
-  ){
-    return rc;
-  }
-
-  /* See if the checksum matches the master journal name */
-  for(u=0; u<len; u++){
-    cksum -= zMaster[u];
-  }
-  if( cksum ){
-    /* If the checksum doesn't add up, then one or more of the disk sectors
-    ** containing the master journal filename is corrupted. This means
-    ** definitely roll back, so just return SQLITE_OK and report a (nul)
-    ** master-journal filename.
-    */
-    len = 0;
-  }
-  zMaster[len] = '\0';
-   
-  return SQLITE_OK;
-}
-
-/*
-** Return the offset of the sector boundary at or immediately 
-** following the value in pPager->journalOff, assuming a sector 
-** size of pPager->sectorSize bytes.
-**
-** i.e for a sector size of 512:
-**
-**   Pager.journalOff          Return value
-**   ---------------------------------------
-**   0                         0
-**   512                       512
-**   100                       512
-**   2000                      2048
-** 
-*/
-static i64 journalHdrOffset(Pager *pPager){
-  i64 offset = 0;
-  i64 c = pPager->journalOff;
-  if( c ){
-    offset = ((c-1)/JOURNAL_HDR_SZ(pPager) + 1) * JOURNAL_HDR_SZ(pPager);
-  }
-  assert( offset%JOURNAL_HDR_SZ(pPager)==0 );
-  assert( offset>=c );
-  assert( (offset-c)<JOURNAL_HDR_SZ(pPager) );
-  return offset;
-}
-
-/*
-** The journal file must be open when this function is called.
-**
-** This function is a no-op if the journal file has not been written to
-** within the current transaction (i.e. if Pager.journalOff==0).
-**
-** If doTruncate is non-zero or the Pager.journalSizeLimit variable is
-** set to 0, then truncate the journal file to zero bytes in size. Otherwise,
-** zero the 28-byte header at the start of the journal file. In either case, 
-** if the pager is not in no-sync mode, sync the journal file immediately 
-** after writing or truncating it.
-**
-** If Pager.journalSizeLimit is set to a positive, non-zero value, and
-** following the truncation or zeroing described above the size of the 
-** journal file in bytes is larger than this value, then truncate the
-** journal file to Pager.journalSizeLimit bytes. The journal file does
-** not need to be synced following this operation.
-**
-** If an IO error occurs, abandon processing and return the IO error code.
-** Otherwise, return SQLITE_OK.
-*/
-static int zeroJournalHdr(Pager *pPager, int doTruncate){
-  int rc = SQLITE_OK;                               /* Return code */
-  assert( isOpen(pPager->jfd) );
-  if( pPager->journalOff ){
-    const i64 iLimit = pPager->journalSizeLimit;    /* Local cache of jsl */
-
-    IOTRACE(("JZEROHDR %p\n", pPager))
-    if( doTruncate || iLimit==0 ){
-      rc = sqlite3OsTruncate(pPager->jfd, 0);
-    }else{
-      static const char zeroHdr[28] = {0};
-      rc = sqlite3OsWrite(pPager->jfd, zeroHdr, sizeof(zeroHdr), 0);
-    }
-    if( rc==SQLITE_OK && !pPager->noSync ){
-      rc = sqlite3OsSync(pPager->jfd, SQLITE_SYNC_DATAONLY|pPager->sync_flags);
-    }
-
-    /* At this point the transaction is committed but the write lock 
-    ** is still held on the file. If there is a size limit configured for 
-    ** the persistent journal and the journal file currently consumes more
-    ** space than that limit allows for, truncate it now. There is no need
-    ** to sync the file following this operation.
-    */
-    if( rc==SQLITE_OK && iLimit>0 ){
-      i64 sz;
-      rc = sqlite3OsFileSize(pPager->jfd, &sz);
-      if( rc==SQLITE_OK && sz>iLimit ){
-        rc = sqlite3OsTruncate(pPager->jfd, iLimit);
-      }
-    }
-  }
-  return rc;
-}
-
-/*
-** The journal file must be open when this routine is called. A journal
-** header (JOURNAL_HDR_SZ bytes) is written into the journal file at the
-** current location.
-**
-** The format for the journal header is as follows:
-** - 8 bytes: Magic identifying journal format.
-** - 4 bytes: Number of records in journal, or -1 no-sync mode is on.
-** - 4 bytes: Random number used for page hash.
-** - 4 bytes: Initial database page count.
-** - 4 bytes: Sector size used by the process that wrote this journal.
-** - 4 bytes: Database page size.
-** 
-** Followed by (JOURNAL_HDR_SZ - 28) bytes of unused space.
-*/
-static int writeJournalHdr(Pager *pPager){
-  int rc = SQLITE_OK;                 /* Return code */
-  char *zHeader = pPager->pTmpSpace;  /* Temporary space used to build header */
-  u32 nHeader = pPager->pageSize;     /* Size of buffer pointed to by zHeader */
-  u32 nWrite;                         /* Bytes of header sector written */
-  int ii;                             /* Loop counter */
-
-  assert( isOpen(pPager->jfd) );      /* Journal file must be open. */
-
-  if( nHeader>JOURNAL_HDR_SZ(pPager) ){
-    nHeader = JOURNAL_HDR_SZ(pPager);
-  }
-
-  /* If there are active savepoints and any of them were created 
-  ** since the most recent journal header was written, update the 
-  ** PagerSavepoint.iHdrOffset fields now.
-  */
-  for(ii=0; ii<pPager->nSavepoint; ii++){
-    if( pPager->aSavepoint[ii].iHdrOffset==0 ){
-      pPager->aSavepoint[ii].iHdrOffset = pPager->journalOff;
-    }
-  }
-
-  pPager->journalHdr = pPager->journalOff = journalHdrOffset(pPager);
-
-  /* 
-  ** Write the nRec Field - the number of page records that follow this
-  ** journal header. Normally, zero is written to this value at this time.
-  ** After the records are added to the journal (and the journal synced, 
-  ** if in full-sync mode), the zero is overwritten with the true number
-  ** of records (see syncJournal()).
-  **
-  ** A faster alternative is to write 0xFFFFFFFF to the nRec field. When
-  ** reading the journal this value tells SQLite to assume that the
-  ** rest of the journal file contains valid page records. This assumption
-  ** is dangerous, as if a failure occurred whilst writing to the journal
-  ** file it may contain some garbage data. There are two scenarios
-  ** where this risk can be ignored:
-  **
-  **   * When the pager is in no-sync mode. Corruption can follow a
-  **     power failure in this case anyway.
-  **
-  **   * When the SQLITE_IOCAP_SAFE_APPEND flag is set. This guarantees
-  **     that garbage data is never appended to the journal file.
-  */
-  assert( isOpen(pPager->fd) || pPager->noSync );
-  if( (pPager->noSync) || (pPager->journalMode==PAGER_JOURNALMODE_MEMORY)
-   || (sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND) 
-  ){
-    memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
-    put32bits(&zHeader[sizeof(aJournalMagic)], 0xffffffff);
-  }else{
-    memset(zHeader, 0, sizeof(aJournalMagic)+4);
-  }
-
-  /* The random check-hash initialiser */ 
-  sqlite3_randomness(sizeof(pPager->cksumInit), &pPager->cksumInit);
-  put32bits(&zHeader[sizeof(aJournalMagic)+4], pPager->cksumInit);
-  /* The initial database size */
-  put32bits(&zHeader[sizeof(aJournalMagic)+8], pPager->dbOrigSize);
-  /* The assumed sector size for this process */
-  put32bits(&zHeader[sizeof(aJournalMagic)+12], pPager->sectorSize);
-
-  /* The page size */
-  put32bits(&zHeader[sizeof(aJournalMagic)+16], pPager->pageSize);
-
-  /* Initializing the tail of the buffer is not necessary.  Everything
-  ** works find if the following memset() is omitted.  But initializing
-  ** the memory prevents valgrind from complaining, so we are willing to
-  ** take the performance hit.
-  */
-  memset(&zHeader[sizeof(aJournalMagic)+20], 0,
-         nHeader-(sizeof(aJournalMagic)+20));
-
-  /* In theory, it is only necessary to write the 28 bytes that the 
-  ** journal header consumes to the journal file here. Then increment the 
-  ** Pager.journalOff variable by JOURNAL_HDR_SZ so that the next 
-  ** record is written to the following sector (leaving a gap in the file
-  ** that will be implicitly filled in by the OS).
-  **
-  ** However it has been discovered that on some systems this pattern can 
-  ** be significantly slower than contiguously writing data to the file,
-  ** even if that means explicitly writing data to the block of 
-  ** (JOURNAL_HDR_SZ - 28) bytes that will not be used. So that is what
-  ** is done. 
-  **
-  ** The loop is required here in case the sector-size is larger than the 
-  ** database page size. Since the zHeader buffer is only Pager.pageSize
-  ** bytes in size, more than one call to sqlite3OsWrite() may be required
-  ** to populate the entire journal header sector.
-  */ 
-  for(nWrite=0; rc==SQLITE_OK&&nWrite<JOURNAL_HDR_SZ(pPager); nWrite+=nHeader){
-    IOTRACE(("JHDR %p %lld %d\n", pPager, pPager->journalHdr, nHeader))
-    rc = sqlite3OsWrite(pPager->jfd, zHeader, nHeader, pPager->journalOff);
-    pPager->journalOff += nHeader;
-  }
-
-  return rc;
-}
-
-/*
-** The journal file must be open when this is called. A journal header file
-** (JOURNAL_HDR_SZ bytes) is read from the current location in the journal
-** file. The current location in the journal file is given by
-** pPager->journalOff. See comments above function writeJournalHdr() for
-** a description of the journal header format.
-**
-** If the header is read successfully, *pNRec is set to the number of
-** page records following this header and *pDbSize is set to the size of the
-** database before the transaction began, in pages. Also, pPager->cksumInit
-** is set to the value read from the journal header. SQLITE_OK is returned
-** in this case.
-**
-** If the journal header file appears to be corrupted, SQLITE_DONE is
-** returned and *pNRec and *PDbSize are undefined.  If JOURNAL_HDR_SZ bytes
-** cannot be read from the journal file an error code is returned.
-*/
-static int readJournalHdr(
-  Pager *pPager,               /* Pager object */
-  int isHot,
-  i64 journalSize,             /* Size of the open journal file in bytes */
-  u32 *pNRec,                  /* OUT: Value read from the nRec field */
-  u32 *pDbSize                 /* OUT: Value of original database size field */
-){
-  int rc;                      /* Return code */
-  unsigned char aMagic[8];     /* A buffer to hold the magic header */
-  i64 iHdrOff;                 /* Offset of journal header being read */
-
-  assert( isOpen(pPager->jfd) );      /* Journal file must be open. */
-
-  /* Advance Pager.journalOff to the start of the next sector. If the
-  ** journal file is too small for there to be a header stored at this
-  ** point, return SQLITE_DONE.
-  */
-  pPager->journalOff = journalHdrOffset(pPager);
-  if( pPager->journalOff+JOURNAL_HDR_SZ(pPager) > journalSize ){
-    return SQLITE_DONE;
-  }
-  iHdrOff = pPager->journalOff;
-
-  /* Read in the first 8 bytes of the journal header. If they do not match
-  ** the  magic string found at the start of each journal header, return
-  ** SQLITE_DONE. If an IO error occurs, return an error code. Otherwise,
-  ** proceed.
-  */
-  if( isHot || iHdrOff!=pPager->journalHdr ){
-    rc = sqlite3OsRead(pPager->jfd, aMagic, sizeof(aMagic), iHdrOff);
-    if( rc ){
-      return rc;
-    }
-    if( memcmp(aMagic, aJournalMagic, sizeof(aMagic))!=0 ){
-      return SQLITE_DONE;
-    }
-  }
-
-  /* Read the first three 32-bit fields of the journal header: The nRec
-  ** field, the checksum-initializer and the database size at the start
-  ** of the transaction. Return an error code if anything goes wrong.
-  */
-  if( SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+8, pNRec))
-   || SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+12, &pPager->cksumInit))
-   || SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+16, pDbSize))
-  ){
-    return rc;
-  }
-
-  if( pPager->journalOff==0 ){
-    u32 iPageSize;               /* Page-size field of journal header */
-    u32 iSectorSize;             /* Sector-size field of journal header */
-    u16 iPageSize16;             /* Copy of iPageSize in 16-bit variable */
-
-    /* Read the page-size and sector-size journal header fields. */
-    if( SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+20, &iSectorSize))
-     || SQLITE_OK!=(rc = read32bits(pPager->jfd, iHdrOff+24, &iPageSize))
-    ){
-      return rc;
-    }
-
-    /* Check that the values read from the page-size and sector-size fields
-    ** are within range. To be 'in range', both values need to be a power
-    ** of two greater than or equal to 512, and not greater than their 
-    ** respective compile time maximum limits.
-    */
-    if( iPageSize<512                  || iSectorSize<512
-     || iPageSize>SQLITE_MAX_PAGE_SIZE || iSectorSize>MAX_SECTOR_SIZE
-     || ((iPageSize-1)&iPageSize)!=0   || ((iSectorSize-1)&iSectorSize)!=0 
-    ){
-      /* If the either the page-size or sector-size in the journal-header is 
-      ** invalid, then the process that wrote the journal-header must have 
-      ** crashed before the header was synced. In this case stop reading 
-      ** the journal file here.
-      */
-      return SQLITE_DONE;
-    }
-
-    /* Update the page-size to match the value read from the journal. 
-    ** Use a testcase() macro to make sure that malloc failure within 
-    ** PagerSetPagesize() is tested.
-    */
-    iPageSize16 = (u16)iPageSize;
-    rc = sqlite3PagerSetPagesize(pPager, &iPageSize16, -1);
-    testcase( rc!=SQLITE_OK );
-    assert( rc!=SQLITE_OK || iPageSize16==(u16)iPageSize );
-
-    /* Update the assumed sector-size to match the value used by 
-    ** the process that created this journal. If this journal was
-    ** created by a process other than this one, then this routine
-    ** is being called from within pager_playback(). The local value
-    ** of Pager.sectorSize is restored at the end of that routine.
-    */
-    pPager->sectorSize = iSectorSize;
-  }
-
-  pPager->journalOff += JOURNAL_HDR_SZ(pPager);
-  return rc;
-}
-
-
-/*
-** Write the supplied master journal name into the journal file for pager
-** pPager at the current location. The master journal name must be the last
-** thing written to a journal file. If the pager is in full-sync mode, the
-** journal file descriptor is advanced to the next sector boundary before
-** anything is written. The format is:
-**
-**   + 4 bytes: PAGER_MJ_PGNO.
-**   + N bytes: Master journal filename in utf-8.
-**   + 4 bytes: N (length of master journal name in bytes, no nul-terminator).
-**   + 4 bytes: Master journal name checksum.
-**   + 8 bytes: aJournalMagic[].
-**
-** The master journal page checksum is the sum of the bytes in the master
-** journal name, where each byte is interpreted as a signed 8-bit integer.
-**
-** If zMaster is a NULL pointer (occurs for a single database transaction), 
-** this call is a no-op.
-*/
-static int writeMasterJournal(Pager *pPager, const char *zMaster){
-  int rc;                          /* Return code */
-  int nMaster;                     /* Length of string zMaster */
-  i64 iHdrOff;                     /* Offset of header in journal file */
-  i64 jrnlSize;                    /* Size of journal file on disk */
-  u32 cksum = 0;                   /* Checksum of string zMaster */
-
-  if( !zMaster || pPager->setMaster
-   || pPager->journalMode==PAGER_JOURNALMODE_MEMORY 
-   || pPager->journalMode==PAGER_JOURNALMODE_OFF 
-  ){
-    return SQLITE_OK;
-  }
-  pPager->setMaster = 1;
-  assert( isOpen(pPager->jfd) );
-
-  /* Calculate the length in bytes and the checksum of zMaster */
-  for(nMaster=0; zMaster[nMaster]; nMaster++){
-    cksum += zMaster[nMaster];
-  }
-
-  /* If in full-sync mode, advance to the next disk sector before writing
-  ** the master journal name. This is in case the previous page written to
-  ** the journal has already been synced.
-  */
-  if( pPager->fullSync ){
-    pPager->journalOff = journalHdrOffset(pPager);
-  }
-  iHdrOff = pPager->journalOff;
-
-  /* Write the master journal data to the end of the journal file. If
-  ** an error occurs, return the error code to the caller.
-  */
-  if( (0 != (rc = write32bits(pPager->jfd, iHdrOff, PAGER_MJ_PGNO(pPager))))
-   || (0 != (rc = sqlite3OsWrite(pPager->jfd, zMaster, nMaster, iHdrOff+4)))
-   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster, nMaster)))
-   || (0 != (rc = write32bits(pPager->jfd, iHdrOff+4+nMaster+4, cksum)))
-   || (0 != (rc = sqlite3OsWrite(pPager->jfd, aJournalMagic, 8, iHdrOff+4+nMaster+8)))
-  ){
-    return rc;
-  }
-  pPager->journalOff += (nMaster+20);
-  pPager->needSync = !pPager->noSync;
-
-  /* If the pager is in peristent-journal mode, then the physical 
-  ** journal-file may extend past the end of the master-journal name
-  ** and 8 bytes of magic data just written to the file. This is 
-  ** dangerous because the code to rollback a hot-journal file
-  ** will not be able to find the master-journal name to determine 
-  ** whether or not the journal is hot. 
-  **
-  ** Easiest thing to do in this scenario is to truncate the journal 
-  ** file to the required size.
-  */ 
-  if( SQLITE_OK==(rc = sqlite3OsFileSize(pPager->jfd, &jrnlSize))
-   && jrnlSize>pPager->journalOff
-  ){
-    rc = sqlite3OsTruncate(pPager->jfd, pPager->journalOff);
-  }
-  return rc;
-}
-
-/*
-** Find a page in the hash table given its page number. Return
-** a pointer to the page or NULL if the requested page is not 
-** already in memory.
-*/
-static PgHdr *pager_lookup(Pager *pPager, Pgno pgno){
-  PgHdr *p;                         /* Return value */
-
-  /* It is not possible for a call to PcacheFetch() with createFlag==0 to
-  ** fail, since no attempt to allocate dynamic memory will be made.
-  */
-  (void)sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &p);
-  return p;
-}
-
-/*
-** Unless the pager is in error-state, discard all in-memory pages. If
-** the pager is in error-state, then this call is a no-op.
-**
-** TODO: Why can we not reset the pager while in error state?
-*/
-static void pager_reset(Pager *pPager){
-  if( SQLITE_OK==pPager->errCode ){
-    sqlite3BackupRestart(pPager->pBackup);
-    sqlite3PcacheClear(pPager->pPCache);
-    pPager->dbSizeValid = 0;
-  }
-}
-
-/*
-** Free all structures in the Pager.aSavepoint[] array and set both
-** Pager.aSavepoint and Pager.nSavepoint to zero. Close the sub-journal
-** if it is open and the pager is not in exclusive mode.
-*/
-static void releaseAllSavepoints(Pager *pPager){
-  int ii;               /* Iterator for looping through Pager.aSavepoint */
-  for(ii=0; ii<pPager->nSavepoint; ii++){
-    sqlite3BitvecDestroy(pPager->aSavepoint[ii].pInSavepoint);
-  }
-  if( !pPager->exclusiveMode || sqlite3IsMemJournal(pPager->sjfd) ){
-    sqlite3OsClose(pPager->sjfd);
-  }
-  sqlite3_free(pPager->aSavepoint);
-  pPager->aSavepoint = 0;
-  pPager->nSavepoint = 0;
-  pPager->nSubRec = 0;
-}
-
-/*
-** Set the bit number pgno in the PagerSavepoint.pInSavepoint 
-** bitvecs of all open savepoints. Return SQLITE_OK if successful
-** or SQLITE_NOMEM if a malloc failure occurs.
-*/
-static int addToSavepointBitvecs(Pager *pPager, Pgno pgno){
-  int ii;                   /* Loop counter */
-  int rc = SQLITE_OK;       /* Result code */
-
-  for(ii=0; ii<pPager->nSavepoint; ii++){
-    PagerSavepoint *p = &pPager->aSavepoint[ii];
-    if( pgno<=p->nOrig ){
-      rc |= sqlite3BitvecSet(p->pInSavepoint, pgno);
-      testcase( rc==SQLITE_NOMEM );
-      assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
-    }
-  }
-  return rc;
-}
-
-/*
-** Unlock the database file. This function is a no-op if the pager
-** is in exclusive mode.
-**
-** If the pager is currently in error state, discard the contents of 
-** the cache and reset the Pager structure internal state. If there is
-** an open journal-file, then the next time a shared-lock is obtained
-** on the pager file (by this or any other process), it will be
-** treated as a hot-journal and rolled back.
-*/
-static void pager_unlock(Pager *pPager){
-  if( !pPager->exclusiveMode ){
-    int rc;                      /* Return code */
-
-    /* Always close the journal file when dropping the database lock.
-    ** Otherwise, another connection with journal_mode=delete might
-    ** delete the file out from under us.
-    */
-    sqlite3OsClose(pPager->jfd);
-    sqlite3BitvecDestroy(pPager->pInJournal);
-    pPager->pInJournal = 0;
-    releaseAllSavepoints(pPager);
-
-    /* If the file is unlocked, somebody else might change it. The
-    ** values stored in Pager.dbSize etc. might become invalid if
-    ** this happens. TODO: Really, this doesn't need to be cleared
-    ** until the change-counter check fails in PagerSharedLock().
-    */
-    pPager->dbSizeValid = 0;
-
-    rc = osUnlock(pPager->fd, NO_LOCK);
-    if( rc ){
-      pPager->errCode = rc;
-    }
-    IOTRACE(("UNLOCK %p\n", pPager))
-
-    /* If Pager.errCode is set, the contents of the pager cache cannot be
-    ** trusted. Now that the pager file is unlocked, the contents of the
-    ** cache can be discarded and the error code safely cleared.
-    */
-    if( pPager->errCode ){
-      if( rc==SQLITE_OK ){
-        pPager->errCode = SQLITE_OK;
-      }
-      pager_reset(pPager);
-    }
-
-    pPager->changeCountDone = 0;
-    pPager->state = PAGER_UNLOCK;
-  }
-}
-
-/*
-** This function should be called when an IOERR, CORRUPT or FULL error
-** may have occurred. The first argument is a pointer to the pager 
-** structure, the second the error-code about to be returned by a pager 
-** API function. The value returned is a copy of the second argument 
-** to this function. 
-**
-** If the second argument is SQLITE_IOERR, SQLITE_CORRUPT, or SQLITE_FULL
-** the error becomes persistent. Until the persisten error is cleared,
-** subsequent API calls on this Pager will immediately return the same 
-** error code.
-**
-** A persistent error indicates that the contents of the pager-cache 
-** cannot be trusted. This state can be cleared by completely discarding 
-** the contents of the pager-cache. If a transaction was active when
-** the persistent error occurred, then the rollback journal may need
-** to be replayed to restore the contents of the database file (as if
-** it were a hot-journal).
-*/
-static int pager_error(Pager *pPager, int rc){
-  int rc2 = rc & 0xff;
-  assert( rc==SQLITE_OK || !MEMDB );
-  assert(
-       pPager->errCode==SQLITE_FULL ||
-       pPager->errCode==SQLITE_OK ||
-       (pPager->errCode & 0xff)==SQLITE_IOERR
-  );
-  if( rc2==SQLITE_FULL || rc2==SQLITE_IOERR ){
-    pPager->errCode = rc;
-  }
-  return rc;
-}
-
-/*
-** Execute a rollback if a transaction is active and unlock the 
-** database file. 
-**
-** If the pager has already entered the error state, do not attempt 
-** the rollback at this time. Instead, pager_unlock() is called. The
-** call to pager_unlock() will discard all in-memory pages, unlock
-** the database file and clear the error state. If this means that
-** there is a hot-journal left in the file-system, the next connection
-** to obtain a shared lock on the pager (which may be this one) will
-** roll it back.
-**
-** If the pager has not already entered the error state, but an IO or
-** malloc error occurs during a rollback, then this will itself cause 
-** the pager to enter the error state. Which will be cleared by the
-** call to pager_unlock(), as described above.
-*/
-static void pagerUnlockAndRollback(Pager *pPager){
-  if( pPager->errCode==SQLITE_OK && pPager->state>=PAGER_RESERVED ){
-    sqlite3BeginBenignMalloc();
-    sqlite3PagerRollback(pPager);
-    sqlite3EndBenignMalloc();
-  }
-  pager_unlock(pPager);
-}
-
-/*
-** This routine ends a transaction. A transaction is usually ended by 
-** either a COMMIT or a ROLLBACK operation. This routine may be called 
-** after rollback of a hot-journal, or if an error occurs while opening
-** the journal file or writing the very first journal-header of a
-** database transaction.
-** 
-** If the pager is in PAGER_SHARED or PAGER_UNLOCK state when this
-** routine is called, it is a no-op (returns SQLITE_OK).
-**
-** Otherwise, any active savepoints are released.
-**
-** If the journal file is open, then it is "finalized". Once a journal 
-** file has been finalized it is not possible to use it to roll back a 
-** transaction. Nor will it be considered to be a hot-journal by this
-** or any other database connection. Exactly how a journal is finalized
-** depends on whether or not the pager is running in exclusive mode and
-** the current journal-mode (Pager.journalMode value), as follows:
-**
-**   journalMode==MEMORY
-**     Journal file descriptor is simply closed. This destroys an 
-**     in-memory journal.
-**
-**   journalMode==TRUNCATE
-**     Journal file is truncated to zero bytes in size.
-**
-**   journalMode==PERSIST
-**     The first 28 bytes of the journal file are zeroed. This invalidates
-**     the first journal header in the file, and hence the entire journal
-**     file. An invalid journal file cannot be rolled back.
-**
-**   journalMode==DELETE
-**     The journal file is closed and deleted using sqlite3OsDelete().
-**
-**     If the pager is running in exclusive mode, this method of finalizing
-**     the journal file is never used. Instead, if the journalMode is
-**     DELETE and the pager is in exclusive mode, the method described under
-**     journalMode==PERSIST is used instead.
-**
-** After the journal is finalized, if running in non-exclusive mode, the
-** pager moves to PAGER_SHARED state (and downgrades the lock on the
-** database file accordingly).
-**
-** If the pager is running in exclusive mode and is in PAGER_SYNCED state,
-** it moves to PAGER_EXCLUSIVE. No locks are downgraded when running in
-** exclusive mode.
-**
-** SQLITE_OK is returned if no error occurs. If an error occurs during
-** any of the IO operations to finalize the journal file or unlock the
-** database then the IO error code is returned to the user. If the 
-** operation to finalize the journal file fails, then the code still
-** tries to unlock the database file if not in exclusive mode. If the
-** unlock operation fails as well, then the first error code related
-** to the first error encountered (the journal finalization one) is
-** returned.
-*/
-static int pager_end_transaction(Pager *pPager, int hasMaster){
-  int rc = SQLITE_OK;      /* Error code from journal finalization operation */
-  int rc2 = SQLITE_OK;     /* Error code from db file unlock operation */
-
-  if( pPager->state<PAGER_RESERVED ){
-    return SQLITE_OK;
-  }
-  releaseAllSavepoints(pPager);
-
-  assert( isOpen(pPager->jfd) || pPager->pInJournal==0 );
-  if( isOpen(pPager->jfd) ){
-
-    /* Finalize the journal file. */
-    if( sqlite3IsMemJournal(pPager->jfd) ){
-      assert( pPager->journalMode==PAGER_JOURNALMODE_MEMORY );
-      sqlite3OsClose(pPager->jfd);
-    }else if( pPager->journalMode==PAGER_JOURNALMODE_TRUNCATE ){
-      if( pPager->journalOff==0 ){
-        rc = SQLITE_OK;
-      }else{
-        rc = sqlite3OsTruncate(pPager->jfd, 0);
-      }
-      pPager->journalOff = 0;
-      pPager->journalStarted = 0;
-    }else if( pPager->exclusiveMode 
-     || pPager->journalMode==PAGER_JOURNALMODE_PERSIST
-    ){
-      rc = zeroJournalHdr(pPager, hasMaster);
-      pager_error(pPager, rc);
-      pPager->journalOff = 0;
-      pPager->journalStarted = 0;
-    }else{
-      /* This branch may be executed with Pager.journalMode==MEMORY if
-      ** a hot-journal was just rolled back. In this case the journal
-      ** file should be closed and deleted. If this connection writes to
-      ** the database file, it will do so using an in-memory journal.  */
-      assert( pPager->journalMode==PAGER_JOURNALMODE_DELETE 
-           || pPager->journalMode==PAGER_JOURNALMODE_MEMORY 
-      );
-      sqlite3OsClose(pPager->jfd);
-      if( !pPager->tempFile ){
-        rc = sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
-      }
-    }
-
-#ifdef SQLITE_CHECK_PAGES
-    sqlite3PcacheIterateDirty(pPager->pPCache, pager_set_pagehash);
-#endif
-
-    sqlite3PcacheCleanAll(pPager->pPCache);
-    sqlite3BitvecDestroy(pPager->pInJournal);
-    pPager->pInJournal = 0;
-    pPager->nRec = 0;
-  }
-
-  if( !pPager->exclusiveMode ){
-    rc2 = osUnlock(pPager->fd, SHARED_LOCK);
-    pPager->state = PAGER_SHARED;
-    pPager->changeCountDone = 0;
-  }else if( pPager->state==PAGER_SYNCED ){
-    pPager->state = PAGER_EXCLUSIVE;
-  }
-  pPager->setMaster = 0;
-  pPager->needSync = 0;
-  pPager->dbModified = 0;
-
-  /* TODO: Is this optimal? Why is the db size invalidated here 
-  ** when the database file is not unlocked? */
-  pPager->dbOrigSize = 0;
-  sqlite3PcacheTruncate(pPager->pPCache, pPager->dbSize);
-  if( !MEMDB ){
-    pPager->dbSizeValid = 0;
-  }
-
-  return (rc==SQLITE_OK?rc2:rc);
-}
-
-/*
-** Parameter aData must point to a buffer of pPager->pageSize bytes
-** of data. Compute and return a checksum based ont the contents of the 
-** page of data and the current value of pPager->cksumInit.
-**
-** This is not a real checksum. It is really just the sum of the 
-** random initial value (pPager->cksumInit) and every 200th byte
-** of the page data, starting with byte offset (pPager->pageSize%200).
-** Each byte is interpreted as an 8-bit unsigned integer.
-**
-** Changing the formula used to compute this checksum results in an
-** incompatible journal file format.
-**
-** If journal corruption occurs due to a power failure, the most likely 
-** scenario is that one end or the other of the record will be changed. 
-** It is much less likely that the two ends of the journal record will be
-** correct and the middle be corrupt.  Thus, this "checksum" scheme,
-** though fast and simple, catches the mostly likely kind of corruption.
-*/
-static u32 pager_cksum(Pager *pPager, const u8 *aData){
-  u32 cksum = pPager->cksumInit;         /* Checksum value to return */
-  int i = pPager->pageSize-200;          /* Loop counter */
-  while( i>0 ){
-    cksum += aData[i];
-    i -= 200;
-  }
-  return cksum;
-}
-
-/*
-** Read a single page from either the journal file (if isMainJrnl==1) or
-** from the sub-journal (if isMainJrnl==0) and playback that page.
-** The page begins at offset *pOffset into the file. The *pOffset
-** value is increased to the start of the next page in the journal.
-**
-** The isMainJrnl flag is true if this is the main rollback journal and
-** false for the statement journal.  The main rollback journal uses
-** checksums - the statement journal does not.
-**
-** If the page number of the page record read from the (sub-)journal file
-** is greater than the current value of Pager.dbSize, then playback is
-** skipped and SQLITE_OK is returned.
-**
-** If pDone is not NULL, then it is a record of pages that have already
-** been played back.  If the page at *pOffset has already been played back
-** (if the corresponding pDone bit is set) then skip the playback.
-** Make sure the pDone bit corresponding to the *pOffset page is set
-** prior to returning.
-**
-** If the page record is successfully read from the (sub-)journal file
-** and played back, then SQLITE_OK is returned. If an IO error occurs
-** while reading the record from the (sub-)journal file or while writing
-** to the database file, then the IO error code is returned. If data
-** is successfully read from the (sub-)journal file but appears to be
-** corrupted, SQLITE_DONE is returned. Data is considered corrupted in
-** two circumstances:
-** 
-**   * If the record page-number is illegal (0 or PAGER_MJ_PGNO), or
-**   * If the record is being rolled back from the main journal file
-**     and the checksum field does not match the record content.
-**
-** Neither of these two scenarios are possible during a savepoint rollback.
-**
-** If this is a savepoint rollback, then memory may have to be dynamically
-** allocated by this function. If this is the case and an allocation fails,
-** SQLITE_NOMEM is returned.
-*/
-static int pager_playback_one_page(
-  Pager *pPager,                /* The pager being played back */
-  int isMainJrnl,               /* 1 -> main journal. 0 -> sub-journal. */
-  int isUnsync,                 /* True if reading from unsynced main journal */
-  i64 *pOffset,                 /* Offset of record to playback */
-  int isSavepnt,                /* True for a savepoint rollback */
-  Bitvec *pDone                 /* Bitvec of pages already played back */
-){
-  int rc;
-  PgHdr *pPg;                   /* An existing page in the cache */
-  Pgno pgno;                    /* The page number of a page in journal */
-  u32 cksum;                    /* Checksum used for sanity checking */
-  u8 *aData;                    /* Temporary storage for the page */
-  sqlite3_file *jfd;            /* The file descriptor for the journal file */
-
-  assert( (isMainJrnl&~1)==0 );      /* isMainJrnl is 0 or 1 */
-  assert( (isSavepnt&~1)==0 );       /* isSavepnt is 0 or 1 */
-  assert( isMainJrnl || pDone );     /* pDone always used on sub-journals */
-  assert( isSavepnt || pDone==0 );   /* pDone never used on non-savepoint */
-
-  aData = (u8*)pPager->pTmpSpace;
-  assert( aData );         /* Temp storage must have already been allocated */
-
-  /* Read the page number and page data from the journal or sub-journal
-  ** file. Return an error code to the caller if an IO error occurs.
-  */
-  jfd = isMainJrnl ? pPager->jfd : pPager->sjfd;
-  rc = read32bits(jfd, *pOffset, &pgno);
-  if( rc!=SQLITE_OK ) return rc;
-  rc = sqlite3OsRead(jfd, aData, pPager->pageSize, (*pOffset)+4);
-  if( rc!=SQLITE_OK ) return rc;
-  *pOffset += pPager->pageSize + 4 + isMainJrnl*4;
-
-  /* Sanity checking on the page.  This is more important that I originally
-  ** thought.  If a power failure occurs while the journal is being written,
-  ** it could cause invalid data to be written into the journal.  We need to
-  ** detect this invalid data (with high probability) and ignore it.
-  */
-  if( pgno==0 || pgno==PAGER_MJ_PGNO(pPager) ){
-    assert( !isSavepnt );
-    return SQLITE_DONE;
-  }
-  if( pgno>(Pgno)pPager->dbSize || sqlite3BitvecTest(pDone, pgno) ){
-    return SQLITE_OK;
-  }
-  if( isMainJrnl ){
-    rc = read32bits(jfd, (*pOffset)-4, &cksum);
-    if( rc ) return rc;
-    if( !isSavepnt && pager_cksum(pPager, aData)!=cksum ){
-      return SQLITE_DONE;
-    }
-  }
-
-  if( pDone && (rc = sqlite3BitvecSet(pDone, pgno))!=SQLITE_OK ){
-    return rc;
-  }
-
-  assert( pPager->state==PAGER_RESERVED || pPager->state>=PAGER_EXCLUSIVE );
-
-  /* If the pager is in RESERVED state, then there must be a copy of this
-  ** page in the pager cache. In this case just update the pager cache,
-  ** not the database file. The page is left marked dirty in this case.
-  **
-  ** An exception to the above rule: If the database is in no-sync mode
-  ** and a page is moved during an incremental vacuum then the page may
-  ** not be in the pager cache. Later: if a malloc() or IO error occurs
-  ** during a Movepage() call, then the page may not be in the cache
-  ** either. So the condition described in the above paragraph is not
-  ** assert()able.
-  **
-  ** If in EXCLUSIVE state, then we update the pager cache if it exists
-  ** and the main file. The page is then marked not dirty.
-  **
-  ** Ticket #1171:  The statement journal might contain page content that is
-  ** different from the page content at the start of the transaction.
-  ** This occurs when a page is changed prior to the start of a statement
-  ** then changed again within the statement.  When rolling back such a
-  ** statement we must not write to the original database unless we know
-  ** for certain that original page contents are synced into the main rollback
-  ** journal.  Otherwise, a power loss might leave modified data in the
-  ** database file without an entry in the rollback journal that can
-  ** restore the database to its original form.  Two conditions must be
-  ** met before writing to the database files. (1) the database must be
-  ** locked.  (2) we know that the original page content is fully synced
-  ** in the main journal either because the page is not in cache or else
-  ** the page is marked as needSync==0.
-  **
-  ** 2008-04-14:  When attempting to vacuum a corrupt database file, it
-  ** is possible to fail a statement on a database that does not yet exist.
-  ** Do not attempt to write if database file has never been opened.
-  */
-  pPg = pager_lookup(pPager, pgno);
-  assert( pPg || !MEMDB );
-  PAGERTRACE(("PLAYBACK %d page %d hash(%08x) %s\n",
-               PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, aData),
-               (isMainJrnl?"main-journal":"sub-journal")
-  ));
-  if( (pPager->state>=PAGER_EXCLUSIVE)
-   && (pPg==0 || 0==(pPg->flags&PGHDR_NEED_SYNC))
-   && isOpen(pPager->fd)
-   && !isUnsync
-  ){
-    i64 ofst = (pgno-1)*(i64)pPager->pageSize;
-    rc = sqlite3OsWrite(pPager->fd, aData, pPager->pageSize, ofst);
-    if( pgno>pPager->dbFileSize ){
-      pPager->dbFileSize = pgno;
-    }
-    if( pPager->pBackup ){
-      CODEC1(pPager, aData, pgno, 3, rc=SQLITE_NOMEM);
-      sqlite3BackupUpdate(pPager->pBackup, pgno, aData);
-      CODEC1(pPager, aData, pgno, 0, rc=SQLITE_NOMEM);
-    }
-  }else if( !isMainJrnl && pPg==0 ){
-    /* If this is a rollback of a savepoint and data was not written to
-    ** the database and the page is not in-memory, there is a potential
-    ** problem. When the page is next fetched by the b-tree layer, it 
-    ** will be read from the database file, which may or may not be 
-    ** current. 
-    **
-    ** There are a couple of different ways this can happen. All are quite
-    ** obscure. When running in synchronous mode, this can only happen 
-    ** if the page is on the free-list at the start of the transaction, then
-    ** populated, then moved using sqlite3PagerMovepage().
-    **
-    ** The solution is to add an in-memory page to the cache containing
-    ** the data just read from the sub-journal. Mark the page as dirty 
-    ** and if the pager requires a journal-sync, then mark the page as 
-    ** requiring a journal-sync before it is written.
-    */
-    assert( isSavepnt );
-    if( (rc = sqlite3PagerAcquire(pPager, pgno, &pPg, 1))!=SQLITE_OK ){
-      return rc;
-    }
-    pPg->flags &= ~PGHDR_NEED_READ;
-    sqlite3PcacheMakeDirty(pPg);
-  }
-  if( pPg ){
-    /* No page should ever be explicitly rolled back that is in use, except
-    ** for page 1 which is held in use in order to keep the lock on the
-    ** database active. However such a page may be rolled back as a result
-    ** of an internal error resulting in an automatic call to
-    ** sqlite3PagerRollback().
-    */
-    void *pData;
-    pData = pPg->pData;
-    memcpy(pData, aData, pPager->pageSize);
-    pPager->xReiniter(pPg);
-    if( isMainJrnl && (!isSavepnt || *pOffset<=pPager->journalHdr) ){
-      /* If the contents of this page were just restored from the main 
-      ** journal file, then its content must be as they were when the 
-      ** transaction was first opened. In this case we can mark the page
-      ** as clean, since there will be no need to write it out to the.
-      **
-      ** There is one exception to this rule. If the page is being rolled
-      ** back as part of a savepoint (or statement) rollback from an 
-      ** unsynced portion of the main journal file, then it is not safe
-      ** to mark the page as clean. This is because marking the page as
-      ** clean will clear the PGHDR_NEED_SYNC flag. Since the page is
-      ** already in the journal file (recorded in Pager.pInJournal) and
-      ** the PGHDR_NEED_SYNC flag is cleared, if the page is written to
-      ** again within this transaction, it will be marked as dirty but
-      ** the PGHDR_NEED_SYNC flag will not be set. It could then potentially
-      ** be written out into the database file before its journal file
-      ** segment is synced. If a crash occurs during or following this,
-      ** database corruption may ensue.
-      */
-      sqlite3PcacheMakeClean(pPg);
-    }
-#ifdef SQLITE_CHECK_PAGES
-    pPg->pageHash = pager_pagehash(pPg);
-#endif
-    /* If this was page 1, then restore the value of Pager.dbFileVers.
-    ** Do this before any decoding. */
-    if( pgno==1 ){
-      memcpy(&pPager->dbFileVers, &((u8*)pData)[24],sizeof(pPager->dbFileVers));
-    }
-
-    /* Decode the page just read from disk */
-    CODEC1(pPager, pData, pPg->pgno, 3, rc=SQLITE_NOMEM);
-    sqlite3PcacheRelease(pPg);
-  }
-  return rc;
-}
-
-/*
-** Parameter zMaster is the name of a master journal file. A single journal
-** file that referred to the master journal file has just been rolled back.
-** This routine checks if it is possible to delete the master journal file,
-** and does so if it is.
-**
-** Argument zMaster may point to Pager.pTmpSpace. So that buffer is not 
-** available for use within this function.
-**
-** When a master journal file is created, it is populated with the names 
-** of all of its child journals, one after another, formatted as utf-8 
-** encoded text. The end of each child journal file is marked with a 
-** nul-terminator byte (0x00). i.e. the entire contents of a master journal
-** file for a transaction involving two databases might be:
-**
-**   "/home/bill/a.db-journal\x00/home/bill/b.db-journal\x00"
-**
-** A master journal file may only be deleted once all of its child 
-** journals have been rolled back.
-**
-** This function reads the contents of the master-journal file into 
-** memory and loops through each of the child journal names. For
-** each child journal, it checks if:
-**
-**   * if the child journal exists, and if so
-**   * if the child journal contains a reference to master journal 
-**     file zMaster
-**
-** If a child journal can be found that matches both of the criteria
-** above, this function returns without doing anything. Otherwise, if
-** no such child journal can be found, file zMaster is deleted from
-** the file-system using sqlite3OsDelete().
-**
-** If an IO error within this function, an error code is returned. This
-** function allocates memory by calling sqlite3Malloc(). If an allocation
-** fails, SQLITE_NOMEM is returned. Otherwise, if no IO or malloc errors 
-** occur, SQLITE_OK is returned.
-**
-** TODO: This function allocates a single block of memory to load
-** the entire contents of the master journal file. This could be
-** a couple of kilobytes or so - potentially larger than the page 
-** size.
-*/
-static int pager_delmaster(Pager *pPager, const char *zMaster){
-  sqlite3_vfs *pVfs = pPager->pVfs;
-  int rc;                   /* Return code */
-  sqlite3_file *pMaster;    /* Malloc'd master-journal file descriptor */
-  sqlite3_file *pJournal;   /* Malloc'd child-journal file descriptor */
-  char *zMasterJournal = 0; /* Contents of master journal file */
-  i64 nMasterJournal;       /* Size of master journal file */
-
-  /* Allocate space for both the pJournal and pMaster file descriptors.
-  ** If successful, open the master journal file for reading.
-  */
-  pMaster = (sqlite3_file *)sqlite3MallocZero(pVfs->szOsFile * 2);
-  pJournal = (sqlite3_file *)(((u8 *)pMaster) + pVfs->szOsFile);
-  if( !pMaster ){
-    rc = SQLITE_NOMEM;
-  }else{
-    const int flags = (SQLITE_OPEN_READONLY|SQLITE_OPEN_MASTER_JOURNAL);
-    rc = sqlite3OsOpen(pVfs, zMaster, pMaster, flags, 0);
-  }
-  if( rc!=SQLITE_OK ) goto delmaster_out;
-
-  rc = sqlite3OsFileSize(pMaster, &nMasterJournal);
-  if( rc!=SQLITE_OK ) goto delmaster_out;
-
-  if( nMasterJournal>0 ){
-    char *zJournal;
-    char *zMasterPtr = 0;
-    int nMasterPtr = pVfs->mxPathname+1;
-
-    /* Load the entire master journal file into space obtained from
-    ** sqlite3_malloc() and pointed to by zMasterJournal. 
-    */
-    zMasterJournal = sqlite3Malloc((int)nMasterJournal + nMasterPtr + 1);
-    if( !zMasterJournal ){
-      rc = SQLITE_NOMEM;
-      goto delmaster_out;
-    }
-    zMasterPtr = &zMasterJournal[nMasterJournal+1];
-    rc = sqlite3OsRead(pMaster, zMasterJournal, (int)nMasterJournal, 0);
-    if( rc!=SQLITE_OK ) goto delmaster_out;
-    zMasterJournal[nMasterJournal] = 0;
-
-    zJournal = zMasterJournal;
-    while( (zJournal-zMasterJournal)<nMasterJournal ){
-      int exists;
-      rc = sqlite3OsAccess(pVfs, zJournal, SQLITE_ACCESS_EXISTS, &exists);
-      if( rc!=SQLITE_OK ){
-        goto delmaster_out;
-      }
-      if( exists ){
-        /* One of the journals pointed to by the master journal exists.
-        ** Open it and check if it points at the master journal. If
-        ** so, return without deleting the master journal file.
-        */
-        int c;
-        int flags = (SQLITE_OPEN_READONLY|SQLITE_OPEN_MAIN_JOURNAL);
-        rc = sqlite3OsOpen(pVfs, zJournal, pJournal, flags, 0);
-        if( rc!=SQLITE_OK ){
-          goto delmaster_out;
-        }
-
-        rc = readMasterJournal(pJournal, zMasterPtr, nMasterPtr);
-        sqlite3OsClose(pJournal);
-        if( rc!=SQLITE_OK ){
-          goto delmaster_out;
-        }
-
-        c = zMasterPtr[0]!=0 && strcmp(zMasterPtr, zMaster)==0;
-        if( c ){
-          /* We have a match. Do not delete the master journal file. */
-          goto delmaster_out;
-        }
-      }
-      zJournal += (sqlite3Strlen30(zJournal)+1);
-    }
-  }
-  
-  rc = sqlite3OsDelete(pVfs, zMaster, 0);
-
-delmaster_out:
-  if( zMasterJournal ){
-    sqlite3_free(zMasterJournal);
-  }  
-  if( pMaster ){
-    sqlite3OsClose(pMaster);
-    assert( !isOpen(pJournal) );
-  }
-  sqlite3_free(pMaster);
-  return rc;
-}
-
-
-/*
-** This function is used to change the actual size of the database 
-** file in the file-system. This only happens when committing a transaction,
-** or rolling back a transaction (including rolling back a hot-journal).
-**
-** If the main database file is not open, or an exclusive lock is not
-** held, this function is a no-op. Otherwise, the size of the file is
-** changed to nPage pages (nPage*pPager->pageSize bytes). If the file
-** on disk is currently larger than nPage pages, then use the VFS
-** xTruncate() method to truncate it.
-**
-** Or, it might might be the case that the file on disk is smaller than 
-** nPage pages. Some operating system implementations can get confused if 
-** you try to truncate a file to some size that is larger than it 
-** currently is, so detect this case and write a single zero byte to 
-** the end of the new file instead.
-**
-** If successful, return SQLITE_OK. If an IO error occurs while modifying
-** the database file, return the error code to the caller.
-*/
-static int pager_truncate(Pager *pPager, Pgno nPage){
-  int rc = SQLITE_OK;
-  if( pPager->state>=PAGER_EXCLUSIVE && isOpen(pPager->fd) ){
-    i64 currentSize, newSize;
-    /* TODO: Is it safe to use Pager.dbFileSize here? */
-    rc = sqlite3OsFileSize(pPager->fd, &currentSize);
-    newSize = pPager->pageSize*(i64)nPage;
-    if( rc==SQLITE_OK && currentSize!=newSize ){
-      if( currentSize>newSize ){
-        rc = sqlite3OsTruncate(pPager->fd, newSize);
-      }else{
-        rc = sqlite3OsWrite(pPager->fd, "", 1, newSize-1);
-      }
-      if( rc==SQLITE_OK ){
-        pPager->dbFileSize = nPage;
-      }
-    }
-  }
-  return rc;
-}
-
-/*
-** Set the value of the Pager.sectorSize variable for the given
-** pager based on the value returned by the xSectorSize method
-** of the open database file. The sector size will be used used 
-** to determine the size and alignment of journal header and 
-** master journal pointers within created journal files.
-**
-** For temporary files the effective sector size is always 512 bytes.
-**
-** Otherwise, for non-temporary files, the effective sector size is
-** the value returned by the xSectorSize() method rounded up to 512 if
-** it is less than 512, or rounded down to MAX_SECTOR_SIZE if it
-** is greater than MAX_SECTOR_SIZE.
-*/
-static void setSectorSize(Pager *pPager){
-  assert( isOpen(pPager->fd) || pPager->tempFile );
-
-  if( !pPager->tempFile ){
-    /* Sector size doesn't matter for temporary files. Also, the file
-    ** may not have been opened yet, in which case the OsSectorSize()
-    ** call will segfault.
-    */
-    pPager->sectorSize = sqlite3OsSectorSize(pPager->fd);
-  }
-  if( pPager->sectorSize<512 ){
-    pPager->sectorSize = 512;
-  }
-  if( pPager->sectorSize>MAX_SECTOR_SIZE ){
-    assert( MAX_SECTOR_SIZE>=512 );
-    pPager->sectorSize = MAX_SECTOR_SIZE;
-  }
-}
-
-/*
-** Playback the journal and thus restore the database file to
-** the state it was in before we started making changes.  
-**
-** The journal file format is as follows: 
-**
-**  (1)  8 byte prefix.  A copy of aJournalMagic[].
-**  (2)  4 byte big-endian integer which is the number of valid page records
-**       in the journal.  If this value is 0xffffffff, then compute the
-**       number of page records from the journal size.
-**  (3)  4 byte big-endian integer which is the initial value for the 
-**       sanity checksum.
-**  (4)  4 byte integer which is the number of pages to truncate the
-**       database to during a rollback.
-**  (5)  4 byte big-endian integer which is the sector size.  The header
-**       is this many bytes in size.
-**  (6)  4 byte big-endian integer which is the page case.
-**  (7)  4 byte integer which is the number of bytes in the master journal
-**       name.  The value may be zero (indicate that there is no master
-**       journal.)
-**  (8)  N bytes of the master journal name.  The name will be nul-terminated
-**       and might be shorter than the value read from (5).  If the first byte
-**       of the name is \000 then there is no master journal.  The master
-**       journal name is stored in UTF-8.
-**  (9)  Zero or more pages instances, each as follows:
-**        +  4 byte page number.
-**        +  pPager->pageSize bytes of data.
-**        +  4 byte checksum
-**
-** When we speak of the journal header, we mean the first 8 items above.
-** Each entry in the journal is an instance of the 9th item.
-**
-** Call the value from the second bullet "nRec".  nRec is the number of
-** valid page entries in the journal.  In most cases, you can compute the
-** value of nRec from the size of the journal file.  But if a power
-** failure occurred while the journal was being written, it could be the
-** case that the size of the journal file had already been increased but
-** the extra entries had not yet made it safely to disk.  In such a case,
-** the value of nRec computed from the file size would be too large.  For
-** that reason, we always use the nRec value in the header.
-**
-** If the nRec value is 0xffffffff it means that nRec should be computed
-** from the file size.  This value is used when the user selects the
-** no-sync option for the journal.  A power failure could lead to corruption
-** in this case.  But for things like temporary table (which will be
-** deleted when the power is restored) we don't care.  
-**
-** If the file opened as the journal file is not a well-formed
-** journal file then all pages up to the first corrupted page are rolled
-** back (or no pages if the journal header is corrupted). The journal file
-** is then deleted and SQLITE_OK returned, just as if no corruption had
-** been encountered.
-**
-** If an I/O or malloc() error occurs, the journal-file is not deleted
-** and an error code is returned.
-**
-** The isHot parameter indicates that we are trying to rollback a journal
-** that might be a hot journal.  Or, it could be that the journal is 
-** preserved because of JOURNALMODE_PERSIST or JOURNALMODE_TRUNCATE.
-** If the journal really is hot, reset the pager cache prior rolling
-** back any content.  If the journal is merely persistent, no reset is
-** needed.
-*/
-static int pager_playback(Pager *pPager, int isHot){
-  sqlite3_vfs *pVfs = pPager->pVfs;
-  i64 szJ;                 /* Size of the journal file in bytes */
-  u32 nRec;                /* Number of Records in the journal */
-  u32 u;                   /* Unsigned loop counter */
-  Pgno mxPg = 0;           /* Size of the original file in pages */
-  int rc;                  /* Result code of a subroutine */
-  int res = 1;             /* Value returned by sqlite3OsAccess() */
-  char *zMaster = 0;       /* Name of master journal file if any */
-  int needPagerReset;      /* True to reset page prior to first page rollback */
-
-  /* Figure out how many records are in the journal.  Abort early if
-  ** the journal is empty.
-  */
-  assert( isOpen(pPager->jfd) );
-  rc = sqlite3OsFileSize(pPager->jfd, &szJ);
-  if( rc!=SQLITE_OK || szJ==0 ){
-    goto end_playback;
-  }
-
-  /* Read the master journal name from the journal, if it is present.
-  ** If a master journal file name is specified, but the file is not
-  ** present on disk, then the journal is not hot and does not need to be
-  ** played back.
-  **
-  ** TODO: Technically the following is an error because it assumes that
-  ** buffer Pager.pTmpSpace is (mxPathname+1) bytes or larger. i.e. that
-  ** (pPager->pageSize >= pPager->pVfs->mxPathname+1). Using os_unix.c,
-  **  mxPathname is 512, which is the same as the minimum allowable value
-  ** for pageSize.
-  */
-  zMaster = pPager->pTmpSpace;
-  rc = readMasterJournal(pPager->jfd, zMaster, pPager->pVfs->mxPathname+1);
-  if( rc==SQLITE_OK && zMaster[0] ){
-    rc = sqlite3OsAccess(pVfs, zMaster, SQLITE_ACCESS_EXISTS, &res);
-  }
-  zMaster = 0;
-  if( rc!=SQLITE_OK || !res ){
-    goto end_playback;
-  }
-  pPager->journalOff = 0;
-  needPagerReset = isHot;
-
-  /* This loop terminates either when a readJournalHdr() or 
-  ** pager_playback_one_page() call returns SQLITE_DONE or an IO error 
-  ** occurs. 
-  */
-  while( 1 ){
-    int isUnsync = 0;
-
-    /* Read the next journal header from the journal file.  If there are
-    ** not enough bytes left in the journal file for a complete header, or
-    ** it is corrupted, then a process must of failed while writing it.
-    ** This indicates nothing more needs to be rolled back.
-    */
-    rc = readJournalHdr(pPager, isHot, szJ, &nRec, &mxPg);
-    if( rc!=SQLITE_OK ){ 
-      if( rc==SQLITE_DONE ){
-        rc = SQLITE_OK;
-      }
-      goto end_playback;
-    }
-
-    /* If nRec is 0xffffffff, then this journal was created by a process
-    ** working in no-sync mode. This means that the rest of the journal
-    ** file consists of pages, there are no more journal headers. Compute
-    ** the value of nRec based on this assumption.
-    */
-    if( nRec==0xffffffff ){
-      assert( pPager->journalOff==JOURNAL_HDR_SZ(pPager) );
-      nRec = (int)((szJ - JOURNAL_HDR_SZ(pPager))/JOURNAL_PG_SZ(pPager));
-    }
-
-    /* If nRec is 0 and this rollback is of a transaction created by this
-    ** process and if this is the final header in the journal, then it means
-    ** that this part of the journal was being filled but has not yet been
-    ** synced to disk.  Compute the number of pages based on the remaining
-    ** size of the file.
-    **
-    ** The third term of the test was added to fix ticket #2565.
-    ** When rolling back a hot journal, nRec==0 always means that the next
-    ** chunk of the journal contains zero pages to be rolled back.  But
-    ** when doing a ROLLBACK and the nRec==0 chunk is the last chunk in
-    ** the journal, it means that the journal might contain additional
-    ** pages that need to be rolled back and that the number of pages 
-    ** should be computed based on the journal file size.
-    */
-    if( nRec==0 && !isHot &&
-        pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff ){
-      nRec = (int)((szJ - pPager->journalOff) / JOURNAL_PG_SZ(pPager));
-      isUnsync = 1;
-    }
-
-    /* If this is the first header read from the journal, truncate the
-    ** database file back to its original size.
-    */
-    if( pPager->journalOff==JOURNAL_HDR_SZ(pPager) ){
-      rc = pager_truncate(pPager, mxPg);
-      if( rc!=SQLITE_OK ){
-        goto end_playback;
-      }
-      pPager->dbSize = mxPg;
-    }
-
-    /* Copy original pages out of the journal and back into the 
-    ** database file and/or page cache.
-    */
-    for(u=0; u<nRec; u++){
-      if( needPagerReset ){
-        pager_reset(pPager);
-        needPagerReset = 0;
-      }
-      rc = pager_playback_one_page(pPager,1,isUnsync,&pPager->journalOff,0,0);
-      if( rc!=SQLITE_OK ){
-        if( rc==SQLITE_DONE ){
-          rc = SQLITE_OK;
-          pPager->journalOff = szJ;
-          break;
-        }else{
-          /* If we are unable to rollback, quit and return the error
-          ** code.  This will cause the pager to enter the error state
-          ** so that no further harm will be done.  Perhaps the next
-          ** process to come along will be able to rollback the database.
-          */
-          goto end_playback;
-        }
-      }
-    }
-  }
-  /*NOTREACHED*/
-  assert( 0 );
-
-end_playback:
-  /* Following a rollback, the database file should be back in its original
-  ** state prior to the start of the transaction, so invoke the
-  ** SQLITE_FCNTL_DB_UNCHANGED file-control method to disable the
-  ** assertion that the transaction counter was modified.
-  */
-  assert(
-    pPager->fd->pMethods==0 ||
-    sqlite3OsFileControl(pPager->fd,SQLITE_FCNTL_DB_UNCHANGED,0)>=SQLITE_OK
-  );
-
-  /* If this playback is happening automatically as a result of an IO or 
-  ** malloc error that occurred after the change-counter was updated but 
-  ** before the transaction was committed, then the change-counter 
-  ** modification may just have been reverted. If this happens in exclusive 
-  ** mode, then subsequent transactions performed by the connection will not
-  ** update the change-counter at all. This may lead to cache inconsistency
-  ** problems for other processes at some point in the future. So, just
-  ** in case this has happened, clear the changeCountDone flag now.
-  */
-  pPager->changeCountDone = pPager->tempFile;
-
-  if( rc==SQLITE_OK ){
-    zMaster = pPager->pTmpSpace;
-    rc = readMasterJournal(pPager->jfd, zMaster, pPager->pVfs->mxPathname+1);
-    testcase( rc!=SQLITE_OK );
-  }
-  if( rc==SQLITE_OK ){
-    rc = pager_end_transaction(pPager, zMaster[0]!='\0');
-    testcase( rc!=SQLITE_OK );
-  }
-  if( rc==SQLITE_OK && zMaster[0] && res ){
-    /* If there was a master journal and this routine will return success,
-    ** see if it is possible to delete the master journal.
-    */
-    rc = pager_delmaster(pPager, zMaster);
-    testcase( rc!=SQLITE_OK );
-  }
-
-  /* The Pager.sectorSize variable may have been updated while rolling
-  ** back a journal created by a process with a different sector size
-  ** value. Reset it to the correct value for this process.
-  */
-  setSectorSize(pPager);
-  return rc;
-}
-
-/*
-** Playback savepoint pSavepoint. Or, if pSavepoint==NULL, then playback
-** the entire master journal file. The case pSavepoint==NULL occurs when 
-** a ROLLBACK TO command is invoked on a SAVEPOINT that is a transaction 
-** savepoint.
-**
-** When pSavepoint is not NULL (meaning a non-transaction savepoint is 
-** being rolled back), then the rollback consists of up to three stages,
-** performed in the order specified:
-**
-**   * Pages are played back from the main journal starting at byte
-**     offset PagerSavepoint.iOffset and continuing to 
-**     PagerSavepoint.iHdrOffset, or to the end of the main journal
-**     file if PagerSavepoint.iHdrOffset is zero.
-**
-**   * If PagerSavepoint.iHdrOffset is not zero, then pages are played
-**     back starting from the journal header immediately following 
-**     PagerSavepoint.iHdrOffset to the end of the main journal file.
-**
-**   * Pages are then played back from the sub-journal file, starting
-**     with the PagerSavepoint.iSubRec and continuing to the end of
-**     the journal file.
-**
-** Throughout the rollback process, each time a page is rolled back, the
-** corresponding bit is set in a bitvec structure (variable pDone in the
-** implementation below). This is used to ensure that a page is only
-** rolled back the first time it is encountered in either journal.
-**
-** If pSavepoint is NULL, then pages are only played back from the main
-** journal file. There is no need for a bitvec in this case.
-**
-** In either case, before playback commences the Pager.dbSize variable
-** is reset to the value that it held at the start of the savepoint 
-** (or transaction). No page with a page-number greater than this value
-** is played back. If one is encountered it is simply skipped.
-*/
-static int pagerPlaybackSavepoint(Pager *pPager, PagerSavepoint *pSavepoint){
-  i64 szJ;                 /* Effective size of the main journal */
-  i64 iHdrOff;             /* End of first segment of main-journal records */
-  int rc = SQLITE_OK;      /* Return code */
-  Bitvec *pDone = 0;       /* Bitvec to ensure pages played back only once */
-
-  assert( pPager->state>=PAGER_SHARED );
-
-  /* Allocate a bitvec to use to store the set of pages rolled back */
-  if( pSavepoint ){
-    pDone = sqlite3BitvecCreate(pSavepoint->nOrig);
-    if( !pDone ){
-      return SQLITE_NOMEM;
-    }
-  }
-
-  /* Set the database size back to the value it was before the savepoint 
-  ** being reverted was opened.
-  */
-  pPager->dbSize = pSavepoint ? pSavepoint->nOrig : pPager->dbOrigSize;
-
-  /* Use pPager->journalOff as the effective size of the main rollback
-  ** journal.  The actual file might be larger than this in
-  ** PAGER_JOURNALMODE_TRUNCATE or PAGER_JOURNALMODE_PERSIST.  But anything
-  ** past pPager->journalOff is off-limits to us.
-  */
-  szJ = pPager->journalOff;
-
-  /* Begin by rolling back records from the main journal starting at
-  ** PagerSavepoint.iOffset and continuing to the next journal header.
-  ** There might be records in the main journal that have a page number
-  ** greater than the current database size (pPager->dbSize) but those
-  ** will be skipped automatically.  Pages are added to pDone as they
-  ** are played back.
-  */
-  if( pSavepoint ){
-    iHdrOff = pSavepoint->iHdrOffset ? pSavepoint->iHdrOffset : szJ;
-    pPager->journalOff = pSavepoint->iOffset;
-    while( rc==SQLITE_OK && pPager->journalOff<iHdrOff ){
-      rc = pager_playback_one_page(pPager, 1, 0, &pPager->journalOff, 1, pDone);
-    }
-    assert( rc!=SQLITE_DONE );
-  }else{
-    pPager->journalOff = 0;
-  }
-
-  /* Continue rolling back records out of the main journal starting at
-  ** the first journal header seen and continuing until the effective end
-  ** of the main journal file.  Continue to skip out-of-range pages and
-  ** continue adding pages rolled back to pDone.
-  */
-  while( rc==SQLITE_OK && pPager->journalOff<szJ ){
-    u32 ii;            /* Loop counter */
-    u32 nJRec = 0;     /* Number of Journal Records */
-    u32 dummy;
-    rc = readJournalHdr(pPager, 0, szJ, &nJRec, &dummy);
-    assert( rc!=SQLITE_DONE );
-
-    /*
-    ** The "pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff"
-    ** test is related to ticket #2565.  See the discussion in the
-    ** pager_playback() function for additional information.
-    */
-    if( nJRec==0 
-     && pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff
-    ){
-      nJRec = (u32)((szJ - pPager->journalOff)/JOURNAL_PG_SZ(pPager));
-    }
-    for(ii=0; rc==SQLITE_OK && ii<nJRec && pPager->journalOff<szJ; ii++){
-      rc = pager_playback_one_page(pPager, 1, 0, &pPager->journalOff, 1, pDone);
-    }
-    assert( rc!=SQLITE_DONE );
-  }
-  assert( rc!=SQLITE_OK || pPager->journalOff==szJ );
-
-  /* Finally,  rollback pages from the sub-journal.  Page that were
-  ** previously rolled back out of the main journal (and are hence in pDone)
-  ** will be skipped.  Out-of-range pages are also skipped.
-  */
-  if( pSavepoint ){
-    u32 ii;            /* Loop counter */
-    i64 offset = pSavepoint->iSubRec*(4+pPager->pageSize);
-    for(ii=pSavepoint->iSubRec; rc==SQLITE_OK && ii<pPager->nSubRec; ii++){
-      assert( offset==ii*(4+pPager->pageSize) );
-      rc = pager_playback_one_page(pPager, 0, 0, &offset, 1, pDone);
-    }
-    assert( rc!=SQLITE_DONE );
-  }
-
-  sqlite3BitvecDestroy(pDone);
-  if( rc==SQLITE_OK ){
-    pPager->journalOff = szJ;
-  }
-  return rc;
-}
-
-/*
-** Change the maximum number of in-memory pages that are allowed.
-*/
-void sqlite3PagerSetCachesize(Pager *pPager, int mxPage){
-  sqlite3PcacheSetCachesize(pPager->pPCache, mxPage);
-}
-
-/*
-** Adjust the robustness of the database to damage due to OS crashes
-** or power failures by changing the number of syncs()s when writing
-** the rollback journal.  There are three levels:
-**
-**    OFF       sqlite3OsSync() is never called.  This is the default
-**              for temporary and transient files.
-**
-**    NORMAL    The journal is synced once before writes begin on the
-**              database.  This is normally adequate protection, but
-**              it is theoretically possible, though very unlikely,
-**              that an inopertune power failure could leave the journal
-**              in a state which would cause damage to the database
-**              when it is rolled back.
-**
-**    FULL      The journal is synced twice before writes begin on the
-**              database (with some additional information - the nRec field
-**              of the journal header - being written in between the two
-**              syncs).  If we assume that writing a
-**              single disk sector is atomic, then this mode provides
-**              assurance that the journal will not be corrupted to the
-**              point of causing damage to the database during rollback.
-**
-** Numeric values associated with these states are OFF==1, NORMAL=2,
-** and FULL=3.
-*/
-#ifndef SQLITE_OMIT_PAGER_PRAGMAS
-void sqlite3PagerSetSafetyLevel(Pager *pPager, int level, int bFullFsync){
-  pPager->noSync =  (level==1 || pPager->tempFile) ?1:0;
-  pPager->fullSync = (level==3 && !pPager->tempFile) ?1:0;
-  pPager->sync_flags = (bFullFsync?SQLITE_SYNC_FULL:SQLITE_SYNC_NORMAL);
-  if( pPager->noSync ) pPager->needSync = 0;
-}
-#endif
-
-/*
-** The following global variable is incremented whenever the library
-** attempts to open a temporary file.  This information is used for
-** testing and analysis only.  
-*/
-#ifdef SQLITE_TEST
-int sqlite3_opentemp_count = 0;
-#endif
-
-/*
-** Open a temporary file.
-**
-** Write the file descriptor into *pFile. Return SQLITE_OK on success 
-** or some other error code if we fail. The OS will automatically 
-** delete the temporary file when it is closed.
-**
-** The flags passed to the VFS layer xOpen() call are those specified
-** by parameter vfsFlags ORed with the following:
-**
-**     SQLITE_OPEN_READWRITE
-**     SQLITE_OPEN_CREATE
-**     SQLITE_OPEN_EXCLUSIVE
-**     SQLITE_OPEN_DELETEONCLOSE
-*/
-static int pagerOpentemp(
-  Pager *pPager,        /* The pager object */
-  sqlite3_file *pFile,  /* Write the file descriptor here */
-  int vfsFlags          /* Flags passed through to the VFS */
-){
-  int rc;               /* Return code */
-
-#ifdef SQLITE_TEST
-  sqlite3_opentemp_count++;  /* Used for testing and analysis only */
-#endif
-
-  vfsFlags |=  SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
-            SQLITE_OPEN_EXCLUSIVE | SQLITE_OPEN_DELETEONCLOSE;
-  rc = sqlite3OsOpen(pPager->pVfs, 0, pFile, vfsFlags, 0);
-  assert( rc!=SQLITE_OK || isOpen(pFile) );
-  return rc;
-}
-
-/*
-** Set the busy handler function.
-**
-** The pager invokes the busy-handler if sqlite3OsLock() returns 
-** SQLITE_BUSY when trying to upgrade from no-lock to a SHARED lock,
-** or when trying to upgrade from a RESERVED lock to an EXCLUSIVE 
-** lock. It does *not* invoke the busy handler when upgrading from
-** SHARED to RESERVED, or when upgrading from SHARED to EXCLUSIVE
-** (which occurs during hot-journal rollback). Summary:
-**
-**   Transition                        | Invokes xBusyHandler
-**   --------------------------------------------------------
-**   NO_LOCK       -> SHARED_LOCK      | Yes
-**   SHARED_LOCK   -> RESERVED_LOCK    | No
-**   SHARED_LOCK   -> EXCLUSIVE_LOCK   | No
-**   RESERVED_LOCK -> EXCLUSIVE_LOCK   | Yes
-**
-** If the busy-handler callback returns non-zero, the lock is 
-** retried. If it returns zero, then the SQLITE_BUSY error is
-** returned to the caller of the pager API function.
-*/
-void sqlite3PagerSetBusyhandler(
-  Pager *pPager,                       /* Pager object */
-  int (*xBusyHandler)(void *),         /* Pointer to busy-handler function */
-  void *pBusyHandlerArg                /* Argument to pass to xBusyHandler */
-){  
-  pPager->xBusyHandler = xBusyHandler;
-  pPager->pBusyHandlerArg = pBusyHandlerArg;
-}
-
-/*
-** Report the current page size and number of reserved bytes back
-** to the codec.
-*/
-#ifdef SQLITE_HAS_CODEC
-static void pagerReportSize(Pager *pPager){
-  if( pPager->xCodecSizeChng ){
-    pPager->xCodecSizeChng(pPager->pCodec, pPager->pageSize,
-                           (int)pPager->nReserve);
-  }
-}
-#else
-# define pagerReportSize(X)     /* No-op if we do not support a codec */
-#endif
-
-/*
-** Change the page size used by the Pager object. The new page size 
-** is passed in *pPageSize.
-**
-** If the pager is in the error state when this function is called, it
-** is a no-op. The value returned is the error state error code (i.e. 
-** one of SQLITE_IOERR, SQLITE_CORRUPT or SQLITE_FULL).
-**
-** Otherwise, if all of the following are true:
-**
-**   * the new page size (value of *pPageSize) is valid (a power 
-**     of two between 512 and SQLITE_MAX_PAGE_SIZE, inclusive), and
-**
-**   * there are no outstanding page references, and
-**
-**   * the database is either not an in-memory database or it is
-**     an in-memory database that currently consists of zero pages.
-**
-** then the pager object page size is set to *pPageSize.
-**
-** If the page size is changed, then this function uses sqlite3PagerMalloc() 
-** to obtain a new Pager.pTmpSpace buffer. If this allocation attempt 
-** fails, SQLITE_NOMEM is returned and the page size remains unchanged. 
-** In all other cases, SQLITE_OK is returned.
-**
-** If the page size is not changed, either because one of the enumerated
-** conditions above is not true, the pager was in error state when this
-** function was called, or because the memory allocation attempt failed, 
-** then *pPageSize is set to the old, retained page size before returning.
-*/
-int sqlite3PagerSetPagesize(Pager *pPager, u16 *pPageSize, int nReserve){
-  int rc = pPager->errCode;
-
-  if( rc==SQLITE_OK ){
-    u16 pageSize = *pPageSize;
-    assert( pageSize==0 || (pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE) );
-    if( (pPager->memDb==0 || pPager->dbSize==0)
-     && sqlite3PcacheRefCount(pPager->pPCache)==0 
-     && pageSize && pageSize!=pPager->pageSize 
-    ){
-      char *pNew = (char *)sqlite3PageMalloc(pageSize);
-      if( !pNew ){
-        rc = SQLITE_NOMEM;
-      }else{
-        pager_reset(pPager);
-        pPager->pageSize = pageSize;
-        sqlite3PageFree(pPager->pTmpSpace);
-        pPager->pTmpSpace = pNew;
-        sqlite3PcacheSetPageSize(pPager->pPCache, pageSize);
-      }
-    }
-    *pPageSize = (u16)pPager->pageSize;
-    if( nReserve<0 ) nReserve = pPager->nReserve;
-    assert( nReserve>=0 && nReserve<1000 );
-    pPager->nReserve = (i16)nReserve;
-    pagerReportSize(pPager);
-  }
-  return rc;
-}
-
-/*
-** Return a pointer to the "temporary page" buffer held internally
-** by the pager.  This is a buffer that is big enough to hold the
-** entire content of a database page.  This buffer is used internally
-** during rollback and will be overwritten whenever a rollback
-** occurs.  But other modules are free to use it too, as long as
-** no rollbacks are happening.
-*/
-void *sqlite3PagerTempSpace(Pager *pPager){
-  return pPager->pTmpSpace;
-}
-
-/*
-** Attempt to set the maximum database page count if mxPage is positive. 
-** Make no changes if mxPage is zero or negative.  And never reduce the
-** maximum page count below the current size of the database.
-**
-** Regardless of mxPage, return the current maximum page count.
-*/
-int sqlite3PagerMaxPageCount(Pager *pPager, int mxPage){
-  if( mxPage>0 ){
-    pPager->mxPgno = mxPage;
-  }
-  sqlite3PagerPagecount(pPager, 0);
-  return pPager->mxPgno;
-}
-
-/*
-** The following set of routines are used to disable the simulated
-** I/O error mechanism.  These routines are used to avoid simulated
-** errors in places where we do not care about errors.
-**
-** Unless -DSQLITE_TEST=1 is used, these routines are all no-ops
-** and generate no code.
-*/
-#ifdef SQLITE_TEST
-extern int sqlite3_io_error_pending;
-extern int sqlite3_io_error_hit;
-static int saved_cnt;
-void disable_simulated_io_errors(void){
-  saved_cnt = sqlite3_io_error_pending;
-  sqlite3_io_error_pending = -1;
-}
-void enable_simulated_io_errors(void){
-  sqlite3_io_error_pending = saved_cnt;
-}
-#else
-# define disable_simulated_io_errors()
-# define enable_simulated_io_errors()
-#endif
-
-/*
-** Read the first N bytes from the beginning of the file into memory
-** that pDest points to. 
-**
-** If the pager was opened on a transient file (zFilename==""), or
-** opened on a file less than N bytes in size, the output buffer is
-** zeroed and SQLITE_OK returned. The rationale for this is that this 
-** function is used to read database headers, and a new transient or
-** zero sized database has a header than consists entirely of zeroes.
-**
-** If any IO error apart from SQLITE_IOERR_SHORT_READ is encountered,
-** the error code is returned to the caller and the contents of the
-** output buffer undefined.
-*/
-int sqlite3PagerReadFileheader(Pager *pPager, int N, unsigned char *pDest){
-  int rc = SQLITE_OK;
-  memset(pDest, 0, N);
-  assert( isOpen(pPager->fd) || pPager->tempFile );
-  if( isOpen(pPager->fd) ){
-    IOTRACE(("DBHDR %p 0 %d\n", pPager, N))
-    rc = sqlite3OsRead(pPager->fd, pDest, N, 0);
-    if( rc==SQLITE_IOERR_SHORT_READ ){
-      rc = SQLITE_OK;
-    }
-  }
-  return rc;
-}
-
-/*
-** Return the total number of pages in the database file associated 
-** with pPager. Normally, this is calculated as (<db file size>/<page-size>).
-** However, if the file is between 1 and <page-size> bytes in size, then 
-** this is considered a 1 page file.
-**
-** If the pager is in error state when this function is called, then the
-** error state error code is returned and *pnPage left unchanged. Or,
-** if the file system has to be queried for the size of the file and
-** the query attempt returns an IO error, the IO error code is returned
-** and *pnPage is left unchanged.
-**
-** Otherwise, if everything is successful, then SQLITE_OK is returned
-** and *pnPage is set to the number of pages in the database.
-*/
-int sqlite3PagerPagecount(Pager *pPager, int *pnPage){
-  Pgno nPage;               /* Value to return via *pnPage */
-
-  /* If the pager is already in the error state, return the error code. */
-  if( pPager->errCode ){
-    return pPager->errCode;
-  }
-
-  /* Determine the number of pages in the file. Store this in nPage. */
-  if( pPager->dbSizeValid ){
-    nPage = pPager->dbSize;
-  }else{
-    int rc;                 /* Error returned by OsFileSize() */
-    i64 n = 0;              /* File size in bytes returned by OsFileSize() */
-
-    assert( isOpen(pPager->fd) || pPager->tempFile );
-    if( isOpen(pPager->fd) && (0 != (rc = sqlite3OsFileSize(pPager->fd, &n))) ){
-      pager_error(pPager, rc);
-      return rc;
-    }
-    if( n>0 && n<pPager->pageSize ){
-      nPage = 1;
-    }else{
-      nPage = (Pgno)(n / pPager->pageSize);
-    }
-    if( pPager->state!=PAGER_UNLOCK ){
-      pPager->dbSize = nPage;
-      pPager->dbFileSize = nPage;
-      pPager->dbSizeValid = 1;
-    }
-  }
-
-  /* If the current number of pages in the file is greater than the 
-  ** configured maximum pager number, increase the allowed limit so
-  ** that the file can be read.
-  */
-  if( nPage>pPager->mxPgno ){
-    pPager->mxPgno = (Pgno)nPage;
-  }
-
-  /* Set the output variable and return SQLITE_OK */
-  if( pnPage ){
-    *pnPage = nPage;
-  }
-  return SQLITE_OK;
-}
-
-
-/*
-** Try to obtain a lock of type locktype on the database file. If
-** a similar or greater lock is already held, this function is a no-op
-** (returning SQLITE_OK immediately).
-**
-** Otherwise, attempt to obtain the lock using sqlite3OsLock(). Invoke 
-** the busy callback if the lock is currently not available. Repeat 
-** until the busy callback returns false or until the attempt to 
-** obtain the lock succeeds.
-**
-** Return SQLITE_OK on success and an error code if we cannot obtain
-** the lock. If the lock is obtained successfully, set the Pager.state 
-** variable to locktype before returning.
-*/
-static int pager_wait_on_lock(Pager *pPager, int locktype){
-  int rc;                              /* Return code */
-
-  /* The OS lock values must be the same as the Pager lock values */
-  assert( PAGER_SHARED==SHARED_LOCK );
-  assert( PAGER_RESERVED==RESERVED_LOCK );
-  assert( PAGER_EXCLUSIVE==EXCLUSIVE_LOCK );
-
-  /* If the file is currently unlocked then the size must be unknown */
-  assert( pPager->state>=PAGER_SHARED || pPager->dbSizeValid==0 );
-
-  /* Check that this is either a no-op (because the requested lock is 
-  ** already held, or one of the transistions that the busy-handler
-  ** may be invoked during, according to the comment above
-  ** sqlite3PagerSetBusyhandler().
-  */
-  assert( (pPager->state>=locktype)
-       || (pPager->state==PAGER_UNLOCK && locktype==PAGER_SHARED)
-       || (pPager->state==PAGER_RESERVED && locktype==PAGER_EXCLUSIVE)
-  );
-
-  if( pPager->state>=locktype ){
-    rc = SQLITE_OK;
-  }else{
-    do {
-      rc = sqlite3OsLock(pPager->fd, locktype);
-    }while( rc==SQLITE_BUSY && pPager->xBusyHandler(pPager->pBusyHandlerArg) );
-    if( rc==SQLITE_OK ){
-      pPager->state = (u8)locktype;
-      IOTRACE(("LOCK %p %d\n", pPager, locktype))
-    }
-  }
-  return rc;
-}
-
-/*
-** Function assertTruncateConstraint(pPager) checks that one of the 
-** following is true for all dirty pages currently in the page-cache:
-**
-**   a) The page number is less than or equal to the size of the 
-**      current database image, in pages, OR
-**
-**   b) if the page content were written at this time, it would not
-**      be necessary to write the current content out to the sub-journal
-**      (as determined by function subjRequiresPage()).
-**
-** If the condition asserted by this function were not true, and the
-** dirty page were to be discarded from the cache via the pagerStress()
-** routine, pagerStress() would not write the current page content to
-** the database file. If a savepoint transaction were rolled back after
-** this happened, the correct behaviour would be to restore the current
-** content of the page. However, since this content is not present in either
-** the database file or the portion of the rollback journal and 
-** sub-journal rolled back the content could not be restored and the
-** database image would become corrupt. It is therefore fortunate that 
-** this circumstance cannot arise.
-*/
-#if defined(SQLITE_DEBUG)
-static void assertTruncateConstraintCb(PgHdr *pPg){
-  assert( pPg->flags&PGHDR_DIRTY );
-  assert( !subjRequiresPage(pPg) || pPg->pgno<=pPg->pPager->dbSize );
-}
-static void assertTruncateConstraint(Pager *pPager){
-  sqlite3PcacheIterateDirty(pPager->pPCache, assertTruncateConstraintCb);
-}
-#else
-# define assertTruncateConstraint(pPager)
-#endif
-
-/*
-** Truncate the in-memory database file image to nPage pages. This 
-** function does not actually modify the database file on disk. It 
-** just sets the internal state of the pager object so that the 
-** truncation will be done when the current transaction is committed.
-*/
-void sqlite3PagerTruncateImage(Pager *pPager, Pgno nPage){
-  assert( pPager->dbSizeValid );
-  assert( pPager->dbSize>=nPage );
-  assert( pPager->state>=PAGER_RESERVED );
-  pPager->dbSize = nPage;
-  assertTruncateConstraint(pPager);
-}
-
-/*
-** Shutdown the page cache.  Free all memory and close all files.
-**
-** If a transaction was in progress when this routine is called, that
-** transaction is rolled back.  All outstanding pages are invalidated
-** and their memory is freed.  Any attempt to use a page associated
-** with this page cache after this function returns will likely
-** result in a coredump.
-**
-** This function always succeeds. If a transaction is active an attempt
-** is made to roll it back. If an error occurs during the rollback 
-** a hot journal may be left in the filesystem but no error is returned
-** to the caller.
-*/
-int sqlite3PagerClose(Pager *pPager){
-  disable_simulated_io_errors();
-  sqlite3BeginBenignMalloc();
-  pPager->errCode = 0;
-  pPager->exclusiveMode = 0;
-  pager_reset(pPager);
-  if( MEMDB ){
-    pager_unlock(pPager);
-  }else{
-    /* Set Pager.journalHdr to -1 for the benefit of the pager_playback() 
-    ** call which may be made from within pagerUnlockAndRollback(). If it
-    ** is not -1, then the unsynced portion of an open journal file may
-    ** be played back into the database. If a power failure occurs while
-    ** this is happening, the database may become corrupt.
-    */
-    pPager->journalHdr = -1;
-    pagerUnlockAndRollback(pPager);
-  }
-  sqlite3EndBenignMalloc();
-  enable_simulated_io_errors();
-  PAGERTRACE(("CLOSE %d\n", PAGERID(pPager)));
-  IOTRACE(("CLOSE %p\n", pPager))
-  sqlite3OsClose(pPager->fd);
-  sqlite3PageFree(pPager->pTmpSpace);
-  sqlite3PcacheClose(pPager->pPCache);
-
-#ifdef SQLITE_HAS_CODEC
-  if( pPager->xCodecFree ) pPager->xCodecFree(pPager->pCodec);
-#endif
-
-  assert( !pPager->aSavepoint && !pPager->pInJournal );
-  assert( !isOpen(pPager->jfd) && !isOpen(pPager->sjfd) );
-
-  sqlite3_free(pPager);
-  return SQLITE_OK;
-}
-
-#if !defined(NDEBUG) || defined(SQLITE_TEST)
-/*
-** Return the page number for page pPg.
-*/
-Pgno sqlite3PagerPagenumber(DbPage *pPg){
-  return pPg->pgno;
-}
-#endif
-
-/*
-** Increment the reference count for page pPg.
-*/
-void sqlite3PagerRef(DbPage *pPg){
-  sqlite3PcacheRef(pPg);
-}
-
-/*
-** Sync the journal. In other words, make sure all the pages that have
-** been written to the journal have actually reached the surface of the
-** disk and can be restored in the event of a hot-journal rollback.
-**
-** If the Pager.needSync flag is not set, then this function is a
-** no-op. Otherwise, the actions required depend on the journal-mode
-** and the device characteristics of the the file-system, as follows:
-**
-**   * If the journal file is an in-memory journal file, no action need
-**     be taken.
-**
-**   * Otherwise, if the device does not support the SAFE_APPEND property,
-**     then the nRec field of the most recently written journal header
-**     is updated to contain the number of journal records that have
-**     been written following it. If the pager is operating in full-sync
-**     mode, then the journal file is synced before this field is updated.
-**
-**   * If the device does not support the SEQUENTIAL property, then 
-**     journal file is synced.
-**
-** Or, in pseudo-code:
-**
-**   if( NOT <in-memory journal> ){
-**     if( NOT SAFE_APPEND ){
-**       if( <full-sync mode> ) xSync(<journal file>);
-**       <update nRec field>
-**     } 
-**     if( NOT SEQUENTIAL ) xSync(<journal file>);
-**   }
-**
-** The Pager.needSync flag is never be set for temporary files, or any
-** file operating in no-sync mode (Pager.noSync set to non-zero).
-**
-** If successful, this routine clears the PGHDR_NEED_SYNC flag of every 
-** page currently held in memory before returning SQLITE_OK. If an IO
-** error is encountered, then the IO error code is returned to the caller.
-*/
-static int syncJournal(Pager *pPager){
-  if( pPager->needSync ){
-    assert( !pPager->tempFile );
-    if( pPager->journalMode!=PAGER_JOURNALMODE_MEMORY ){
-      int rc;                              /* Return code */
-      const int iDc = sqlite3OsDeviceCharacteristics(pPager->fd);
-      assert( isOpen(pPager->jfd) );
-
-      if( 0==(iDc&SQLITE_IOCAP_SAFE_APPEND) ){
-        /* This block deals with an obscure problem. If the last connection
-        ** that wrote to this database was operating in persistent-journal
-        ** mode, then the journal file may at this point actually be larger
-        ** than Pager.journalOff bytes. If the next thing in the journal
-        ** file happens to be a journal-header (written as part of the
-        ** previous connections transaction), and a crash or power-failure 
-        ** occurs after nRec is updated but before this connection writes 
-        ** anything else to the journal file (or commits/rolls back its 
-        ** transaction), then SQLite may become confused when doing the 
-        ** hot-journal rollback following recovery. It may roll back all
-        ** of this connections data, then proceed to rolling back the old,
-        ** out-of-date data that follows it. Database corruption.
-        **
-        ** To work around this, if the journal file does appear to contain
-        ** a valid header following Pager.journalOff, then write a 0x00
-        ** byte to the start of it to prevent it from being recognized.
-        **
-        ** Variable iNextHdrOffset is set to the offset at which this
-        ** problematic header will occur, if it exists. aMagic is used 
-        ** as a temporary buffer to inspect the first couple of bytes of
-        ** the potential journal header.
-        */
-        i64 iNextHdrOffset;
-        u8 aMagic[8];
-        u8 zHeader[sizeof(aJournalMagic)+4];
-
-        memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
-        put32bits(&zHeader[sizeof(aJournalMagic)], pPager->nRec);
-
-        iNextHdrOffset = journalHdrOffset(pPager);
-        rc = sqlite3OsRead(pPager->jfd, aMagic, 8, iNextHdrOffset);
-        if( rc==SQLITE_OK && 0==memcmp(aMagic, aJournalMagic, 8) ){
-          static const u8 zerobyte = 0;
-          rc = sqlite3OsWrite(pPager->jfd, &zerobyte, 1, iNextHdrOffset);
-        }
-        if( rc!=SQLITE_OK && rc!=SQLITE_IOERR_SHORT_READ ){
-          return rc;
-        }
-
-        /* Write the nRec value into the journal file header. If in
-        ** full-synchronous mode, sync the journal first. This ensures that
-        ** all data has really hit the disk before nRec is updated to mark
-        ** it as a candidate for rollback.
-        **
-        ** This is not required if the persistent media supports the
-        ** SAFE_APPEND property. Because in this case it is not possible 
-        ** for garbage data to be appended to the file, the nRec field
-        ** is populated with 0xFFFFFFFF when the journal header is written
-        ** and never needs to be updated.
-        */
-        if( pPager->fullSync && 0==(iDc&SQLITE_IOCAP_SEQUENTIAL) ){
-          PAGERTRACE(("SYNC journal of %d\n", PAGERID(pPager)));
-          IOTRACE(("JSYNC %p\n", pPager))
-          rc = sqlite3OsSync(pPager->jfd, pPager->sync_flags);
-          if( rc!=SQLITE_OK ) return rc;
-        }
-        IOTRACE(("JHDR %p %lld\n", pPager, pPager->journalHdr));
-        rc = sqlite3OsWrite(
-            pPager->jfd, zHeader, sizeof(zHeader), pPager->journalHdr
-        );
-        if( rc!=SQLITE_OK ) return rc;
-      }
-      if( 0==(iDc&SQLITE_IOCAP_SEQUENTIAL) ){
-        PAGERTRACE(("SYNC journal of %d\n", PAGERID(pPager)));
-        IOTRACE(("JSYNC %p\n", pPager))
-        rc = sqlite3OsSync(pPager->jfd, pPager->sync_flags| 
-          (pPager->sync_flags==SQLITE_SYNC_FULL?SQLITE_SYNC_DATAONLY:0)
-        );
-        if( rc!=SQLITE_OK ) return rc;
-      }
-    }
-
-    /* The journal file was just successfully synced. Set Pager.needSync 
-    ** to zero and clear the PGHDR_NEED_SYNC flag on all pagess.
-    */
-    pPager->needSync = 0;
-    pPager->journalStarted = 1;
-    sqlite3PcacheClearSyncFlags(pPager->pPCache);
-  }
-
-  return SQLITE_OK;
-}
-
-/*
-** The argument is the first in a linked list of dirty pages connected
-** by the PgHdr.pDirty pointer. This function writes each one of the
-** in-memory pages in the list to the database file. The argument may
-** be NULL, representing an empty list. In this case this function is
-** a no-op.
-**
-** The pager must hold at least a RESERVED lock when this function
-** is called. Before writing anything to the database file, this lock
-** is upgraded to an EXCLUSIVE lock. If the lock cannot be obtained,
-** SQLITE_BUSY is returned and no data is written to the database file.
-** 
-** If the pager is a temp-file pager and the actual file-system file
-** is not yet open, it is created and opened before any data is 
-** written out.
-**
-** Once the lock has been upgraded and, if necessary, the file opened,
-** the pages are written out to the database file in list order. Writing
-** a page is skipped if it meets either of the following criteria:
-**
-**   * The page number is greater than Pager.dbSize, or
-**   * The PGHDR_DONT_WRITE flag is set on the page.
-**
-** If writing out a page causes the database file to grow, Pager.dbFileSize
-** is updated accordingly. If page 1 is written out, then the value cached
-** in Pager.dbFileVers[] is updated to match the new value stored in
-** the database file.
-**
-** If everything is successful, SQLITE_OK is returned. If an IO error 
-** occurs, an IO error code is returned. Or, if the EXCLUSIVE lock cannot
-** be obtained, SQLITE_BUSY is returned.
-*/
-static int pager_write_pagelist(PgHdr *pList){
-  Pager *pPager;                       /* Pager object */
-  int rc;                              /* Return code */
-
-  if( NEVER(pList==0) ) return SQLITE_OK;
-  pPager = pList->pPager;
-
-  /* At this point there may be either a RESERVED or EXCLUSIVE lock on the
-  ** database file. If there is already an EXCLUSIVE lock, the following
-  ** call is a no-op.
-  **
-  ** Moving the lock from RESERVED to EXCLUSIVE actually involves going
-  ** through an intermediate state PENDING.   A PENDING lock prevents new
-  ** readers from attaching to the database but is unsufficient for us to
-  ** write.  The idea of a PENDING lock is to prevent new readers from
-  ** coming in while we wait for existing readers to clear.
-  **
-  ** While the pager is in the RESERVED state, the original database file
-  ** is unchanged and we can rollback without having to playback the
-  ** journal into the original database file.  Once we transition to
-  ** EXCLUSIVE, it means the database file has been changed and any rollback
-  ** will require a journal playback.
-  */
-  assert( pPager->state>=PAGER_RESERVED );
-  rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
-
-  /* If the file is a temp-file has not yet been opened, open it now. It
-  ** is not possible for rc to be other than SQLITE_OK if this branch
-  ** is taken, as pager_wait_on_lock() is a no-op for temp-files.
-  */
-  if( !isOpen(pPager->fd) ){
-    assert( pPager->tempFile && rc==SQLITE_OK );
-    rc = pagerOpentemp(pPager, pPager->fd, pPager->vfsFlags);
-  }
-
-  while( rc==SQLITE_OK && pList ){
-    Pgno pgno = pList->pgno;
-
-    /* If there are dirty pages in the page cache with page numbers greater
-    ** than Pager.dbSize, this means sqlite3PagerTruncateImage() was called to
-    ** make the file smaller (presumably by auto-vacuum code). Do not write
-    ** any such pages to the file.
-    **
-    ** Also, do not write out any page that has the PGHDR_DONT_WRITE flag
-    ** set (set by sqlite3PagerDontWrite()).
-    */
-    if( pgno<=pPager->dbSize && 0==(pList->flags&PGHDR_DONT_WRITE) ){
-      i64 offset = (pgno-1)*(i64)pPager->pageSize;   /* Offset to write */
-      char *pData;                                   /* Data to write */    
-
-      /* Encode the database */
-      CODEC2(pPager, pList->pData, pgno, 6, return SQLITE_NOMEM, pData);
-
-      /* Write out the page data. */
-      rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize, offset);
-
-      /* If page 1 was just written, update Pager.dbFileVers to match
-      ** the value now stored in the database file. If writing this 
-      ** page caused the database file to grow, update dbFileSize. 
-      */
-      if( pgno==1 ){
-        memcpy(&pPager->dbFileVers, &pData[24], sizeof(pPager->dbFileVers));
-      }
-      if( pgno>pPager->dbFileSize ){
-        pPager->dbFileSize = pgno;
-      }
-
-      /* Update any backup objects copying the contents of this pager. */
-      sqlite3BackupUpdate(pPager->pBackup, pgno, (u8*)pList->pData);
-
-      PAGERTRACE(("STORE %d page %d hash(%08x)\n",
-                   PAGERID(pPager), pgno, pager_pagehash(pList)));
-      IOTRACE(("PGOUT %p %d\n", pPager, pgno));
-      PAGER_INCR(sqlite3_pager_writedb_count);
-      PAGER_INCR(pPager->nWrite);
-    }else{
-      PAGERTRACE(("NOSTORE %d page %d\n", PAGERID(pPager), pgno));
-    }
-#ifdef SQLITE_CHECK_PAGES
-    pList->pageHash = pager_pagehash(pList);
-#endif
-    pList = pList->pDirty;
-  }
-
-  return rc;
-}
-
-/*
-** Append a record of the current state of page pPg to the sub-journal. 
-** It is the callers responsibility to use subjRequiresPage() to check 
-** that it is really required before calling this function.
-**
-** If successful, set the bit corresponding to pPg->pgno in the bitvecs
-** for all open savepoints before returning.
-**
-** This function returns SQLITE_OK if everything is successful, an IO
-** error code if the attempt to write to the sub-journal fails, or 
-** SQLITE_NOMEM if a malloc fails while setting a bit in a savepoint
-** bitvec.
-*/
-static int subjournalPage(PgHdr *pPg){
-  int rc = SQLITE_OK;
-  Pager *pPager = pPg->pPager;
-  if( isOpen(pPager->sjfd) ){
-    void *pData = pPg->pData;
-    i64 offset = pPager->nSubRec*(4+pPager->pageSize);
-    char *pData2;
-
-    CODEC2(pPager, pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
-    PAGERTRACE(("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno));
-  
-    assert( pageInJournal(pPg) || pPg->pgno>pPager->dbOrigSize );
-    rc = write32bits(pPager->sjfd, offset, pPg->pgno);
-    if( rc==SQLITE_OK ){
-      rc = sqlite3OsWrite(pPager->sjfd, pData2, pPager->pageSize, offset+4);
-    }
-  }
-  if( rc==SQLITE_OK ){
-    pPager->nSubRec++;
-    assert( pPager->nSavepoint>0 );
-    rc = addToSavepointBitvecs(pPager, pPg->pgno);
-  }
-  return rc;
-}
-
-
-/*
-** This function is called by the pcache layer when it has reached some
-** soft memory limit. The first argument is a pointer to a Pager object
-** (cast as a void*). The pager is always 'purgeable' (not an in-memory
-** database). The second argument is a reference to a page that is 
-** currently dirty but has no outstanding references. The page
-** is always associated with the Pager object passed as the first 
-** argument.
-**
-** The job of this function is to make pPg clean by writing its contents
-** out to the database file, if possible. This may involve syncing the
-** journal file. 
-**
-** If successful, sqlite3PcacheMakeClean() is called on the page and
-** SQLITE_OK returned. If an IO error occurs while trying to make the
-** page clean, the IO error code is returned. If the page cannot be
-** made clean for some other reason, but no error occurs, then SQLITE_OK
-** is returned by sqlite3PcacheMakeClean() is not called.
-*/
-static int pagerStress(void *p, PgHdr *pPg){
-  Pager *pPager = (Pager *)p;
-  int rc = SQLITE_OK;
-
-  assert( pPg->pPager==pPager );
-  assert( pPg->flags&PGHDR_DIRTY );
-
-  /* The doNotSync flag is set by the sqlite3PagerWrite() function while it
-  ** is journalling a set of two or more database pages that are stored
-  ** on the same disk sector. Syncing the journal is not allowed while
-  ** this is happening as it is important that all members of such a
-  ** set of pages are synced to disk together. So, if the page this function
-  ** is trying to make clean will require a journal sync and the doNotSync
-  ** flag is set, return without doing anything. The pcache layer will
-  ** just have to go ahead and allocate a new page buffer instead of
-  ** reusing pPg.
-  **
-  ** Similarly, if the pager has already entered the error state, do not
-  ** try to write the contents of pPg to disk.
-  */
-  if( NEVER(pPager->errCode)
-   || (pPager->doNotSync && pPg->flags&PGHDR_NEED_SYNC)
-  ){
-    return SQLITE_OK;
-  }
-
-  /* Sync the journal file if required. */
-  if( pPg->flags&PGHDR_NEED_SYNC ){
-    rc = syncJournal(pPager);
-    if( rc==SQLITE_OK && pPager->fullSync && 
-      !(pPager->journalMode==PAGER_JOURNALMODE_MEMORY) &&
-      !(sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND)
-    ){
-      pPager->nRec = 0;
-      rc = writeJournalHdr(pPager);
-    }
-  }
-
-  /* If the page number of this page is larger than the current size of
-  ** the database image, it may need to be written to the sub-journal.
-  ** This is because the call to pager_write_pagelist() below will not
-  ** actually write data to the file in this case.
-  **
-  ** Consider the following sequence of events:
-  **
-  **   BEGIN;
-  **     <journal page X>
-  **     <modify page X>
-  **     SAVEPOINT sp;
-  **       <shrink database file to Y pages>
-  **       pagerStress(page X)
-  **     ROLLBACK TO sp;
-  **
-  ** If (X>Y), then when pagerStress is called page X will not be written
-  ** out to the database file, but will be dropped from the cache. Then,
-  ** following the "ROLLBACK TO sp" statement, reading page X will read
-  ** data from the database file. This will be the copy of page X as it
-  ** was when the transaction started, not as it was when "SAVEPOINT sp"
-  ** was executed.
-  **
-  ** The solution is to write the current data for page X into the 
-  ** sub-journal file now (if it is not already there), so that it will
-  ** be restored to its current value when the "ROLLBACK TO sp" is 
-  ** executed.
-  */
-  if( NEVER(
-      rc==SQLITE_OK && pPg->pgno>pPager->dbSize && subjRequiresPage(pPg)
-  ) ){
-    rc = subjournalPage(pPg);
-  }
-
-  /* Write the contents of the page out to the database file. */
-  if( rc==SQLITE_OK ){
-    pPg->pDirty = 0;
-    rc = pager_write_pagelist(pPg);
-  }
-
-  /* Mark the page as clean. */
-  if( rc==SQLITE_OK ){
-    PAGERTRACE(("STRESS %d page %d\n", PAGERID(pPager), pPg->pgno));
-    sqlite3PcacheMakeClean(pPg);
-  }
-
-  return pager_error(pPager, rc);
-}
-
-
-/*
-** Allocate and initialize a new Pager object and put a pointer to it
-** in *ppPager. The pager should eventually be freed by passing it
-** to sqlite3PagerClose().
-**
-** The zFilename argument is the path to the database file to open.
-** If zFilename is NULL then a randomly-named temporary file is created
-** and used as the file to be cached. Temporary files are be deleted
-** automatically when they are closed. If zFilename is ":memory:" then 
-** all information is held in cache. It is never written to disk. 
-** This can be used to implement an in-memory database.
-**
-** The nExtra parameter specifies the number of bytes of space allocated
-** along with each page reference. This space is available to the user
-** via the sqlite3PagerGetExtra() API.
-**
-** The flags argument is used to specify properties that affect the
-** operation of the pager. It should be passed some bitwise combination
-** of the PAGER_OMIT_JOURNAL and PAGER_NO_READLOCK flags.
-**
-** The vfsFlags parameter is a bitmask to pass to the flags parameter
-** of the xOpen() method of the supplied VFS when opening files. 
-**
-** If the pager object is allocated and the specified file opened 
-** successfully, SQLITE_OK is returned and *ppPager set to point to
-** the new pager object. If an error occurs, *ppPager is set to NULL
-** and error code returned. This function may return SQLITE_NOMEM
-** (sqlite3Malloc() is used to allocate memory), SQLITE_CANTOPEN or 
-** various SQLITE_IO_XXX errors.
-*/
-int sqlite3PagerOpen(
-  sqlite3_vfs *pVfs,       /* The virtual file system to use */
-  Pager **ppPager,         /* OUT: Return the Pager structure here */
-  const char *zFilename,   /* Name of the database file to open */
-  int nExtra,              /* Extra bytes append to each in-memory page */
-  int flags,               /* flags controlling this file */
-  int vfsFlags,            /* flags passed through to sqlite3_vfs.xOpen() */
-  void (*xReinit)(DbPage*) /* Function to reinitialize pages */
-){
-  u8 *pPtr;
-  Pager *pPager = 0;       /* Pager object to allocate and return */
-  int rc = SQLITE_OK;      /* Return code */
-  int tempFile = 0;        /* True for temp files (incl. in-memory files) */
-  int memDb = 0;           /* True if this is an in-memory file */
-  int readOnly = 0;        /* True if this is a read-only file */
-  int journalFileSize;     /* Bytes to allocate for each journal fd */
-  char *zPathname = 0;     /* Full path to database file */
-  int nPathname = 0;       /* Number of bytes in zPathname */
-  int useJournal = (flags & PAGER_OMIT_JOURNAL)==0; /* False to omit journal */
-  int noReadlock = (flags & PAGER_NO_READLOCK)!=0;  /* True to omit read-lock */
-  int pcacheSize = sqlite3PcacheSize();       /* Bytes to allocate for PCache */
-  u16 szPageDflt = SQLITE_DEFAULT_PAGE_SIZE;  /* Default page size */
-
-  /* Figure out how much space is required for each journal file-handle
-  ** (there are two of them, the main journal and the sub-journal). This
-  ** is the maximum space required for an in-memory journal file handle 
-  ** and a regular journal file-handle. Note that a "regular journal-handle"
-  ** may be a wrapper capable of caching the first portion of the journal
-  ** file in memory to implement the atomic-write optimization (see 
-  ** source file journal.c).
-  */
-  if( sqlite3JournalSize(pVfs)>sqlite3MemJournalSize() ){
-    journalFileSize = ROUND8(sqlite3JournalSize(pVfs));
-  }else{
-    journalFileSize = ROUND8(sqlite3MemJournalSize());
-  }
-
-  /* Set the output variable to NULL in case an error occurs. */
-  *ppPager = 0;
-
-  /* Compute and store the full pathname in an allocated buffer pointed
-  ** to by zPathname, length nPathname. Or, if this is a temporary file,
-  ** leave both nPathname and zPathname set to 0.
-  */
-  if( zFilename && zFilename[0] ){
-    nPathname = pVfs->mxPathname+1;
-    zPathname = sqlite3Malloc(nPathname*2);
-    if( zPathname==0 ){
-      return SQLITE_NOMEM;
-    }
-#ifndef SQLITE_OMIT_MEMORYDB
-    if( strcmp(zFilename,":memory:")==0 ){
-      memDb = 1;
-      zPathname[0] = 0;
-    }else
-#endif
-    {
-      zPathname[0] = 0; /* Make sure initialized even if FullPathname() fails */
-      rc = sqlite3OsFullPathname(pVfs, zFilename, nPathname, zPathname);
-    }
-
-    nPathname = sqlite3Strlen30(zPathname);
-    if( rc==SQLITE_OK && nPathname+8>pVfs->mxPathname ){
-      /* This branch is taken when the journal path required by
-      ** the database being opened will be more than pVfs->mxPathname
-      ** bytes in length. This means the database cannot be opened,
-      ** as it will not be possible to open the journal file or even
-      ** check for a hot-journal before reading.
-      */
-      rc = SQLITE_CANTOPEN;
-    }
-    if( rc!=SQLITE_OK ){
-      sqlite3_free(zPathname);
-      return rc;
-    }
-  }
-
-  /* Allocate memory for the Pager structure, PCache object, the
-  ** three file descriptors, the database file name and the journal 
-  ** file name. The layout in memory is as follows:
-  **
-  **     Pager object                    (sizeof(Pager) bytes)
-  **     PCache object                   (sqlite3PcacheSize() bytes)
-  **     Database file handle            (pVfs->szOsFile bytes)
-  **     Sub-journal file handle         (journalFileSize bytes)
-  **     Main journal file handle        (journalFileSize bytes)
-  **     Database file name              (nPathname+1 bytes)
-  **     Journal file name               (nPathname+8+1 bytes)
-  */
-  pPtr = (u8 *)sqlite3MallocZero(
-    ROUND8(sizeof(*pPager)) +      /* Pager structure */
-    ROUND8(pcacheSize) +           /* PCache object */
-    ROUND8(pVfs->szOsFile) +       /* The main db file */
-    journalFileSize * 2 +          /* The two journal files */ 
-    nPathname + 1 +                /* zFilename */
-    nPathname + 8 + 1              /* zJournal */
-  );
-  assert( EIGHT_BYTE_ALIGNMENT(SQLITE_INT_TO_PTR(journalFileSize)) );
-  if( !pPtr ){
-    sqlite3_free(zPathname);
-    return SQLITE_NOMEM;
-  }
-  pPager =              (Pager*)(pPtr);
-  pPager->pPCache =    (PCache*)(pPtr += ROUND8(sizeof(*pPager)));
-  pPager->fd =   (sqlite3_file*)(pPtr += ROUND8(pcacheSize));
-  pPager->sjfd = (sqlite3_file*)(pPtr += ROUND8(pVfs->szOsFile));
-  pPager->jfd =  (sqlite3_file*)(pPtr += journalFileSize);
-  pPager->zFilename =    (char*)(pPtr += journalFileSize);
-  assert( EIGHT_BYTE_ALIGNMENT(pPager->jfd) );
-
-  /* Fill in the Pager.zFilename and Pager.zJournal buffers, if required. */
-  if( zPathname ){
-    pPager->zJournal =   (char*)(pPtr += nPathname + 1);
-    memcpy(pPager->zFilename, zPathname, nPathname);
-    memcpy(pPager->zJournal, zPathname, nPathname);
-    memcpy(&pPager->zJournal[nPathname], "-journal", 8);
-    if( pPager->zFilename[0]==0 ) pPager->zJournal[0] = 0;
-    sqlite3_free(zPathname);
-  }
-  pPager->pVfs = pVfs;
-  pPager->vfsFlags = vfsFlags;
-
-  /* Open the pager file.
-  */
-  if( zFilename && zFilename[0] && !memDb ){
-    int fout = 0;                    /* VFS flags returned by xOpen() */
-    rc = sqlite3OsOpen(pVfs, pPager->zFilename, pPager->fd, vfsFlags, &fout);
-    readOnly = (fout&SQLITE_OPEN_READONLY);
-
-    /* If the file was successfully opened for read/write access,
-    ** choose a default page size in case we have to create the
-    ** database file. The default page size is the maximum of:
-    **
-    **    + SQLITE_DEFAULT_PAGE_SIZE,
-    **    + The value returned by sqlite3OsSectorSize()
-    **    + The largest page size that can be written atomically.
-    */
-    if( rc==SQLITE_OK && !readOnly ){
-      setSectorSize(pPager);
-      assert(SQLITE_DEFAULT_PAGE_SIZE<=SQLITE_MAX_DEFAULT_PAGE_SIZE);
-      if( szPageDflt<pPager->sectorSize ){
-        if( pPager->sectorSize>SQLITE_MAX_DEFAULT_PAGE_SIZE ){
-          szPageDflt = SQLITE_MAX_DEFAULT_PAGE_SIZE;
-        }else{
-          szPageDflt = (u16)pPager->sectorSize;
-        }
-      }
-#ifdef SQLITE_ENABLE_ATOMIC_WRITE
-      {
-        int iDc = sqlite3OsDeviceCharacteristics(pPager->fd);
-        int ii;
-        assert(SQLITE_IOCAP_ATOMIC512==(512>>8));
-        assert(SQLITE_IOCAP_ATOMIC64K==(65536>>8));
-        assert(SQLITE_MAX_DEFAULT_PAGE_SIZE<=65536);
-        for(ii=szPageDflt; ii<=SQLITE_MAX_DEFAULT_PAGE_SIZE; ii=ii*2){
-          if( iDc&(SQLITE_IOCAP_ATOMIC|(ii>>8)) ){
-            szPageDflt = ii;
-          }
-        }
-      }
-#endif
-    }
-  }else{
-    /* If a temporary file is requested, it is not opened immediately.
-    ** In this case we accept the default page size and delay actually
-    ** opening the file until the first call to OsWrite().
-    **
-    ** This branch is also run for an in-memory database. An in-memory
-    ** database is the same as a temp-file that is never written out to
-    ** disk and uses an in-memory rollback journal.
-    */ 
-    tempFile = 1;
-    pPager->state = PAGER_EXCLUSIVE;
-    readOnly = (vfsFlags&SQLITE_OPEN_READONLY);
-  }
-
-  /* The following call to PagerSetPagesize() serves to set the value of 
-  ** Pager.pageSize and to allocate the Pager.pTmpSpace buffer.
-  */
-  if( rc==SQLITE_OK ){
-    assert( pPager->memDb==0 );
-    rc = sqlite3PagerSetPagesize(pPager, &szPageDflt, -1);
-    testcase( rc!=SQLITE_OK );
-  }
-
-  /* If an error occurred in either of the blocks above, free the 
-  ** Pager structure and close the file.
-  */
-  if( rc!=SQLITE_OK ){
-    assert( !pPager->pTmpSpace );
-    sqlite3OsClose(pPager->fd);
-    sqlite3_free(pPager);
-    return rc;
-  }
-
-  /* Initialize the PCache object. */
-  assert( nExtra<1000 );
-  nExtra = ROUND8(nExtra);
-  sqlite3PcacheOpen(szPageDflt, nExtra, !memDb,
-                    !memDb?pagerStress:0, (void *)pPager, pPager->pPCache);
-
-  PAGERTRACE(("OPEN %d %s\n", FILEHANDLEID(pPager->fd), pPager->zFilename));
-  IOTRACE(("OPEN %p %s\n", pPager, pPager->zFilename))
-
-  pPager->useJournal = (u8)useJournal;
-  pPager->noReadlock = (noReadlock && readOnly) ?1:0;
-  /* pPager->stmtOpen = 0; */
-  /* pPager->stmtInUse = 0; */
-  /* pPager->nRef = 0; */
-  pPager->dbSizeValid = (u8)memDb;
-  /* pPager->stmtSize = 0; */
-  /* pPager->stmtJSize = 0; */
-  /* pPager->nPage = 0; */
-  pPager->mxPgno = SQLITE_MAX_PAGE_COUNT;
-  /* pPager->state = PAGER_UNLOCK; */
-  assert( pPager->state == (tempFile ? PAGER_EXCLUSIVE : PAGER_UNLOCK) );
-  /* pPager->errMask = 0; */
-  pPager->tempFile = (u8)tempFile;
-  assert( tempFile==PAGER_LOCKINGMODE_NORMAL 
-          || tempFile==PAGER_LOCKINGMODE_EXCLUSIVE );
-  assert( PAGER_LOCKINGMODE_EXCLUSIVE==1 );
-  pPager->exclusiveMode = (u8)tempFile; 
-  pPager->changeCountDone = pPager->tempFile;
-  pPager->memDb = (u8)memDb;
-  pPager->readOnly = (u8)readOnly;
-  /* pPager->needSync = 0; */
-  assert( useJournal || pPager->tempFile );
-  pPager->noSync = pPager->tempFile;
-  pPager->fullSync = pPager->noSync ?0:1;
-  pPager->sync_flags = SQLITE_SYNC_NORMAL;
-  /* pPager->pFirst = 0; */
-  /* pPager->pFirstSynced = 0; */
-  /* pPager->pLast = 0; */
-  pPager->nExtra = (u16)nExtra;
-  pPager->journalSizeLimit = SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT;
-  assert( isOpen(pPager->fd) || tempFile );
-  setSectorSize(pPager);
-  if( !useJournal ){
-    pPager->journalMode = PAGER_JOURNALMODE_OFF;
-  }else if( memDb ){
-    pPager->journalMode = PAGER_JOURNALMODE_MEMORY;
-  }
-  /* pPager->xBusyHandler = 0; */
-  /* pPager->pBusyHandlerArg = 0; */
-  pPager->xReiniter = xReinit;
-  /* memset(pPager->aHash, 0, sizeof(pPager->aHash)); */
-  *ppPager = pPager;
-  return SQLITE_OK;
-}
-
-
-
-/*
-** This function is called after transitioning from PAGER_UNLOCK to
-** PAGER_SHARED state. It tests if there is a hot journal present in
-** the file-system for the given pager. A hot journal is one that 
-** needs to be played back. According to this function, a hot-journal
-** file exists if the following criteria are met:
-**
-**   * The journal file exists in the file system, and
-**   * No process holds a RESERVED or greater lock on the database file, and
-**   * The database file itself is greater than 0 bytes in size, and
-**   * The first byte of the journal file exists and is not 0x00.
-**
-** If the current size of the database file is 0 but a journal file
-** exists, that is probably an old journal left over from a prior
-** database with the same name. In this case the journal file is
-** just deleted using OsDelete, *pExists is set to 0 and SQLITE_OK
-** is returned.
-**
-** This routine does not check if there is a master journal filename
-** at the end of the file. If there is, and that master journal file
-** does not exist, then the journal file is not really hot. In this
-** case this routine will return a false-positive. The pager_playback()
-** routine will discover that the journal file is not really hot and 
-** will not roll it back. 
-**
-** If a hot-journal file is found to exist, *pExists is set to 1 and 
-** SQLITE_OK returned. If no hot-journal file is present, *pExists is
-** set to 0 and SQLITE_OK returned. If an IO error occurs while trying
-** to determine whether or not a hot-journal file exists, the IO error
-** code is returned and the value of *pExists is undefined.
-*/
-static int hasHotJournal(Pager *pPager, int *pExists){
-  sqlite3_vfs * const pVfs = pPager->pVfs;
-  int rc;                       /* Return code */
-  int exists;                   /* True if a journal file is present */
-
-  assert( pPager!=0 );
-  assert( pPager->useJournal );
-  assert( isOpen(pPager->fd) );
-  assert( !isOpen(pPager->jfd) );
-  assert( pPager->state <= PAGER_SHARED );
-
-  *pExists = 0;
-  rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
-  if( rc==SQLITE_OK && exists ){
-    int locked;                 /* True if some process holds a RESERVED lock */
-
-    /* Race condition here:  Another process might have been holding the
-    ** the RESERVED lock and have a journal open at the sqlite3OsAccess() 
-    ** call above, but then delete the journal and drop the lock before
-    ** we get to the following sqlite3OsCheckReservedLock() call.  If that
-    ** is the case, this routine might think there is a hot journal when
-    ** in fact there is none.  This results in a false-positive which will
-    ** be dealt with by the playback routine.  Ticket #3883.
-    */
-    rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
-    if( rc==SQLITE_OK && !locked ){
-      int nPage;
-
-      /* Check the size of the database file. If it consists of 0 pages,
-      ** then delete the journal file. See the header comment above for 
-      ** the reasoning here.  Delete the obsolete journal file under
-      ** a RESERVED lock to avoid race conditions and to avoid violating
-      ** [H33020].
-      */
-      rc = sqlite3PagerPagecount(pPager, &nPage);
-      if( rc==SQLITE_OK ){
-        if( nPage==0 ){
-          sqlite3BeginBenignMalloc();
-          if( sqlite3OsLock(pPager->fd, RESERVED_LOCK)==SQLITE_OK ){
-            sqlite3OsDelete(pVfs, pPager->zJournal, 0);
-            sqlite3OsUnlock(pPager->fd, SHARED_LOCK);
-          }
-          sqlite3EndBenignMalloc();
-        }else{
-          /* The journal file exists and no other connection has a reserved
-          ** or greater lock on the database file. Now check that there is
-          ** at least one non-zero bytes at the start of the journal file.
-          ** If there is, then we consider this journal to be hot. If not, 
-          ** it can be ignored.
-          */
-          int f = SQLITE_OPEN_READONLY|SQLITE_OPEN_MAIN_JOURNAL;
-          rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, f, &f);
-          if( rc==SQLITE_OK ){
-            u8 first = 0;
-            rc = sqlite3OsRead(pPager->jfd, (void *)&first, 1, 0);
-            if( rc==SQLITE_IOERR_SHORT_READ ){
-              rc = SQLITE_OK;
-            }
-            sqlite3OsClose(pPager->jfd);
-            *pExists = (first!=0);
-          }else if( rc==SQLITE_CANTOPEN ){
-            /* If we cannot open the rollback journal file in order to see if
-            ** its has a zero header, that might be due to an I/O error, or
-            ** it might be due to the race condition described above and in
-            ** ticket #3883.  Either way, assume that the journal is hot.
-            ** This might be a false positive.  But if it is, then the
-            ** automatic journal playback and recovery mechanism will deal
-            ** with it under an EXCLUSIVE lock where we do not need to
-            ** worry so much with race conditions.
-            */
-            *pExists = 1;
-            rc = SQLITE_OK;
-          }
-        }
-      }
-    }
-  }
-
-  return rc;
-}
-
-/*
-** Read the content for page pPg out of the database file and into 
-** pPg->pData. A shared lock or greater must be held on the database
-** file before this function is called.
-**
-** If page 1 is read, then the value of Pager.dbFileVers[] is set to
-** the value read from the database file.
-**
-** If an IO error occurs, then the IO error is returned to the caller.
-** Otherwise, SQLITE_OK is returned.
-*/
-static int readDbPage(PgHdr *pPg){
-  Pager *pPager = pPg->pPager; /* Pager object associated with page pPg */
-  Pgno pgno = pPg->pgno;       /* Page number to read */
-  int rc;                      /* Return code */
-  i64 iOffset;                 /* Byte offset of file to read from */
-
-  assert( pPager->state>=PAGER_SHARED && !MEMDB );
-  assert( isOpen(pPager->fd) );
-
-  if( NEVER(!isOpen(pPager->fd)) ){
-    assert( pPager->tempFile );
-    memset(pPg->pData, 0, pPager->pageSize);
-    return SQLITE_OK;
-  }
-  iOffset = (pgno-1)*(i64)pPager->pageSize;
-  rc = sqlite3OsRead(pPager->fd, pPg->pData, pPager->pageSize, iOffset);
-  if( rc==SQLITE_IOERR_SHORT_READ ){
-    rc = SQLITE_OK;
-  }
-  if( pgno==1 ){
-    u8 *dbFileVers = &((u8*)pPg->pData)[24];
-    memcpy(&pPager->dbFileVers, dbFileVers, sizeof(pPager->dbFileVers));
-  }
-  CODEC1(pPager, pPg->pData, pgno, 3, rc = SQLITE_NOMEM);
-
-  PAGER_INCR(sqlite3_pager_readdb_count);
-  PAGER_INCR(pPager->nRead);
-  IOTRACE(("PGIN %p %d\n", pPager, pgno));
-  PAGERTRACE(("FETCH %d page %d hash(%08x)\n",
-               PAGERID(pPager), pgno, pager_pagehash(pPg)));
-
-  return rc;
-}
-
-/*
-** This function is called to obtain a shared lock on the database file.
-** It is illegal to call sqlite3PagerAcquire() until after this function
-** has been successfully called. If a shared-lock is already held when
-** this function is called, it is a no-op.
-**
-** The following operations are also performed by this function.
-**
-**   1) If the pager is currently in PAGER_UNLOCK state (no lock held
-**      on the database file), then an attempt is made to obtain a
-**      SHARED lock on the database file. Immediately after obtaining
-**      the SHARED lock, the file-system is checked for a hot-journal,
-**      which is played back if present. Following any hot-journal 
-**      rollback, the contents of the cache are validated by checking
-**      the 'change-counter' field of the database file header and
-**      discarded if they are found to be invalid.
-**
-**   2) If the pager is running in exclusive-mode, and there are currently
-**      no outstanding references to any pages, and is in the error state,
-**      then an attempt is made to clear the error state by discarding
-**      the contents of the page cache and rolling back any open journal
-**      file.
-**
-** If the operation described by (2) above is not attempted, and if the
-** pager is in an error state other than SQLITE_FULL when this is called,
-** the error state error code is returned. It is permitted to read the
-** database when in SQLITE_FULL error state.
-**
-** Otherwise, if everything is successful, SQLITE_OK is returned. If an
-** IO error occurs while locking the database, checking for a hot-journal
-** file or rolling back a journal file, the IO error code is returned.
-*/
-int sqlite3PagerSharedLock(Pager *pPager){
-  int rc = SQLITE_OK;                /* Return code */
-  int isErrorReset = 0;              /* True if recovering from error state */
-
-  /* This routine is only called from b-tree and only when there are no
-  ** outstanding pages */
-  assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
-  if( NEVER(MEMDB && pPager->errCode) ){ return pPager->errCode; }
-
-  /* If this database is in an error-state, now is a chance to clear
-  ** the error. Discard the contents of the pager-cache and rollback
-  ** any hot journal in the file-system.
-  */
-  if( pPager->errCode ){
-    if( isOpen(pPager->jfd) || pPager->zJournal ){
-      isErrorReset = 1;
-    }
-    pPager->errCode = SQLITE_OK;
-    pager_reset(pPager);
-  }
-
-  if( pPager->state==PAGER_UNLOCK || isErrorReset ){
-    sqlite3_vfs * const pVfs = pPager->pVfs;
-    int isHotJournal = 0;
-    assert( !MEMDB );
-    assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
-    if( pPager->noReadlock ){
-      assert( pPager->readOnly );
-      pPager->state = PAGER_SHARED;
-    }else{
-      rc = pager_wait_on_lock(pPager, SHARED_LOCK);
-      if( rc!=SQLITE_OK ){
-        assert( pPager->state==PAGER_UNLOCK );
-        return pager_error(pPager, rc);
-      }
-    }
-    assert( pPager->state>=SHARED_LOCK );
-
-    /* If a journal file exists, and there is no RESERVED lock on the
-    ** database file, then it either needs to be played back or deleted.
-    */
-    if( !isErrorReset ){
-      assert( pPager->state <= PAGER_SHARED );
-      rc = hasHotJournal(pPager, &isHotJournal);
-      if( rc!=SQLITE_OK ){
-        goto failed;
-      }
-    }
-    if( isErrorReset || isHotJournal ){
-      /* Get an EXCLUSIVE lock on the database file. At this point it is
-      ** important that a RESERVED lock is not obtained on the way to the
-      ** EXCLUSIVE lock. If it were, another process might open the
-      ** database file, detect the RESERVED lock, and conclude that the
-      ** database is safe to read while this process is still rolling the 
-      ** hot-journal back.
-      ** 
-      ** Because the intermediate RESERVED lock is not requested, any
-      ** other process attempting to access the database file will get to 
-      ** this point in the code and fail to obtain its own EXCLUSIVE lock 
-      ** on the database file.
-      */
-      if( pPager->state<EXCLUSIVE_LOCK ){
-        rc = sqlite3OsLock(pPager->fd, EXCLUSIVE_LOCK);
-        if( rc!=SQLITE_OK ){
-          rc = pager_error(pPager, rc);
-          goto failed;
-        }
-        pPager->state = PAGER_EXCLUSIVE;
-      }
- 
-      /* Open the journal for read/write access. This is because in 
-      ** exclusive-access mode the file descriptor will be kept open and
-      ** possibly used for a transaction later on. On some systems, the
-      ** OsTruncate() call used in exclusive-access mode also requires
-      ** a read/write file handle.
-      */
-      if( !isOpen(pPager->jfd) ){
-        int res;
-        rc = sqlite3OsAccess(pVfs,pPager->zJournal,SQLITE_ACCESS_EXISTS,&res);
-        if( rc==SQLITE_OK ){
-          if( res ){
-            int fout = 0;
-            int f = SQLITE_OPEN_READWRITE|SQLITE_OPEN_MAIN_JOURNAL;
-            assert( !pPager->tempFile );
-            rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, f, &fout);
-            assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
-            if( rc==SQLITE_OK && fout&SQLITE_OPEN_READONLY ){
-              rc = SQLITE_CANTOPEN;
-              sqlite3OsClose(pPager->jfd);
-            }
-          }else{
-            /* If the journal does not exist, it usually means that some 
-            ** other connection managed to get in and roll it back before 
-            ** this connection obtained the exclusive lock above. Or, it 
-            ** may mean that the pager was in the error-state when this
-            ** function was called and the journal file does not exist.  */
-            rc = pager_end_transaction(pPager, 0);
-          }
-        }
-      }
-      if( rc!=SQLITE_OK ){
-        goto failed;
-      }
-
-      /* TODO: Why are these cleared here? Is it necessary? */
-      pPager->journalStarted = 0;
-      pPager->journalOff = 0;
-      pPager->setMaster = 0;
-      pPager->journalHdr = 0;
- 
-      /* Playback and delete the journal.  Drop the database write
-      ** lock and reacquire the read lock. Purge the cache before
-      ** playing back the hot-journal so that we don't end up with
-      ** an inconsistent cache.
-      */
-      if( isOpen(pPager->jfd) ){
-        rc = pager_playback(pPager, 1);
-        if( rc!=SQLITE_OK ){
-          rc = pager_error(pPager, rc);
-          goto failed;
-        }
-      }
-      assert( (pPager->state==PAGER_SHARED)
-           || (pPager->exclusiveMode && pPager->state>PAGER_SHARED)
-      );
-    }
-
-    if( pPager->pBackup || sqlite3PcachePagecount(pPager->pPCache)>0 ){
-      /* The shared-lock has just been acquired on the database file
-      ** and there are already pages in the cache (from a previous
-      ** read or write transaction).  Check to see if the database
-      ** has been modified.  If the database has changed, flush the
-      ** cache.
-      **
-      ** Database changes is detected by looking at 15 bytes beginning
-      ** at offset 24 into the file.  The first 4 of these 16 bytes are
-      ** a 32-bit counter that is incremented with each change.  The
-      ** other bytes change randomly with each file change when
-      ** a codec is in use.
-      ** 
-      ** There is a vanishingly small chance that a change will not be 
-      ** detected.  The chance of an undetected change is so small that
-      ** it can be neglected.
-      */
-      char dbFileVers[sizeof(pPager->dbFileVers)];
-      sqlite3PagerPagecount(pPager, 0);
-
-      if( pPager->errCode ){
-        rc = pPager->errCode;
-        goto failed;
-      }
-
-      assert( pPager->dbSizeValid );
-      if( pPager->dbSize>0 ){
-        IOTRACE(("CKVERS %p %d\n", pPager, sizeof(dbFileVers)));
-        rc = sqlite3OsRead(pPager->fd, &dbFileVers, sizeof(dbFileVers), 24);
-        if( rc!=SQLITE_OK ){
-          goto failed;
-        }
-      }else{
-        memset(dbFileVers, 0, sizeof(dbFileVers));
-      }
-
-      if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
-        pager_reset(pPager);
-      }
-    }
-    assert( pPager->exclusiveMode || pPager->state==PAGER_SHARED );
-  }
-
- failed:
-  if( rc!=SQLITE_OK ){
-    /* pager_unlock() is a no-op for exclusive mode and in-memory databases. */
-    pager_unlock(pPager);
-  }
-  return rc;
-}
-
-/*
-** If the reference count has reached zero, rollback any active
-** transaction and unlock the pager.
-**
-** Except, in locking_mode=EXCLUSIVE when there is nothing to in
-** the rollback journal, the unlock is not performed and there is
-** nothing to rollback, so this routine is a no-op.
-*/ 
-static void pagerUnlockIfUnused(Pager *pPager){
-  if( (sqlite3PcacheRefCount(pPager->pPCache)==0)
-   && (!pPager->exclusiveMode || pPager->journalOff>0) 
-  ){
-    pagerUnlockAndRollback(pPager);
-  }
-}
-
-/*
-** Acquire a reference to page number pgno in pager pPager (a page
-** reference has type DbPage*). If the requested reference is 
-** successfully obtained, it is copied to *ppPage and SQLITE_OK returned.
-**
-** If the requested page is already in the cache, it is returned. 
-** Otherwise, a new page object is allocated and populated with data
-** read from the database file. In some cases, the pcache module may
-** choose not to allocate a new page object and may reuse an existing
-** object with no outstanding references.
-**
-** The extra data appended to a page is always initialized to zeros the 
-** first time a page is loaded into memory. If the page requested is 
-** already in the cache when this function is called, then the extra
-** data is left as it was when the page object was last used.
-**
-** If the database image is smaller than the requested page or if a 
-** non-zero value is passed as the noContent parameter and the 
-** requested page is not already stored in the cache, then no 
-** actual disk read occurs. In this case the memory image of the 
-** page is initialized to all zeros. 
-**
-** If noContent is true, it means that we do not care about the contents
-** of the page. This occurs in two seperate scenarios:
-**
-**   a) When reading a free-list leaf page from the database, and
-**
-**   b) When a savepoint is being rolled back and we need to load
-**      a new page into the cache to populate with the data read
-**      from the savepoint journal.
-**
-** If noContent is true, then the data returned is zeroed instead of
-** being read from the database. Additionally, the bits corresponding
-** to pgno in Pager.pInJournal (bitvec of pages already written to the
-** journal file) and the PagerSavepoint.pInSavepoint bitvecs of any open
-** savepoints are set. This means if the page is made writable at any
-** point in the future, using a call to sqlite3PagerWrite(), its contents
-** will not be journaled. This saves IO.
-**
-** The acquisition might fail for several reasons.  In all cases,
-** an appropriate error code is returned and *ppPage is set to NULL.
-**
-** See also sqlite3PagerLookup().  Both this routine and Lookup() attempt
-** to find a page in the in-memory cache first.  If the page is not already
-** in memory, this routine goes to disk to read it in whereas Lookup()
-** just returns 0.  This routine acquires a read-lock the first time it
-** has to go to disk, and could also playback an old journal if necessary.
-** Since Lookup() never goes to disk, it never has to deal with locks
-** or journal files.
-*/
-int sqlite3PagerAcquire(
-  Pager *pPager,      /* The pager open on the database file */
-  Pgno pgno,          /* Page number to fetch */
-  DbPage **ppPage,    /* Write a pointer to the page here */
-  int noContent       /* Do not bother reading content from disk if true */
-){
-  /* This just passes through to our modified version with NULL data. */
-  return sqlite3PagerAcquire2(pPager, pgno, ppPage, noContent, 0);
-}
-
-/*
-** This is an internal version of sqlite3PagerAcquire that takes an extra
-** parameter of data to use to fill the page with. This allows more efficient
-** filling for preloaded data. If this extra parameter is NULL, we'll go to
-** the file.
-**
-** See sqlite3PagerLoadall which uses this function.
-*/
-int sqlite3PagerAcquire2(
-  Pager *pPager,      /* The pager open on the database file */
-  Pgno pgno,          /* Page number to fetch */
-  DbPage **ppPage,    /* Write a pointer to the page here */
-  int noContent,      /* Do not bother reading content from disk if true */
-  unsigned char* pDataToFill
-){
-  int rc;
-  PgHdr *pPg;
-
-  assert( assert_pager_state(pPager) );
-  assert( pPager->state>PAGER_UNLOCK );
-
-  if( pgno==0 ){
-    return SQLITE_CORRUPT_BKPT;
-  }
-
-  /* If the pager is in the error state, return an error immediately. 
-  ** Otherwise, request the page from the PCache layer. */
-  if( pPager->errCode!=SQLITE_OK && pPager->errCode!=SQLITE_FULL ){
-    rc = pPager->errCode;
-  }else{
-    rc = sqlite3PcacheFetch(pPager->pPCache, pgno, 1, ppPage);
-  }
-
-  if( rc!=SQLITE_OK ){
-    /* Either the call to sqlite3PcacheFetch() returned an error or the
-    ** pager was already in the error-state when this function was called.
-    ** Set pPg to 0 and jump to the exception handler.  */
-    pPg = 0;
-    goto pager_acquire_err;
-  }
-  assert( (*ppPage)->pgno==pgno );
-  assert( (*ppPage)->pPager==pPager || (*ppPage)->pPager==0 );
-
-  if( (*ppPage)->pPager ){
-    /* In this case the pcache already contains an initialized copy of
-    ** the page. Return without further ado.  */
-    assert( pgno<=PAGER_MAX_PGNO && pgno!=PAGER_MJ_PGNO(pPager) );
-    PAGER_INCR(pPager->nHit);
-    return SQLITE_OK;
-
-  }else{
-    /* The pager cache has created a new page. Its content needs to 
-    ** be initialized.  */
-    int nMax;
-
-    PAGER_INCR(pPager->nMiss);
-    pPg = *ppPage;
-    pPg->pPager = pPager;
-
-    /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
-    ** number greater than this, or the unused locking-page, is requested. */
-    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
-      rc = SQLITE_CORRUPT_BKPT;
-      goto pager_acquire_err;
-    }
-
-    rc = sqlite3PagerPagecount(pPager, &nMax);
-    if( rc!=SQLITE_OK ){
-      goto pager_acquire_err;
-    }
-
-    if( nMax<(int)pgno || MEMDB || noContent ){
-      if( pgno>pPager->mxPgno ){
-        rc = SQLITE_FULL;
-        goto pager_acquire_err;
-      }
-      if( noContent ){
-        /* Failure to set the bits in the InJournal bit-vectors is benign.
-        ** It merely means that we might do some extra work to journal a 
-        ** page that does not need to be journaled.  Nevertheless, be sure 
-        ** to test the case where a malloc error occurs while trying to set 
-        ** a bit in a bit vector.
-        */
-        sqlite3BeginBenignMalloc();
-        if( pgno<=pPager->dbOrigSize ){
-          TESTONLY( rc = ) sqlite3BitvecSet(pPager->pInJournal, pgno);
-          testcase( rc==SQLITE_NOMEM );
-        }
-        TESTONLY( rc = ) addToSavepointBitvecs(pPager, pgno);
-        testcase( rc==SQLITE_NOMEM );
-        sqlite3EndBenignMalloc();
-      }else{
-        memset(pPg->pData, 0, pPager->pageSize);
-      }
-      IOTRACE(("ZERO %p %d\n", pPager, pgno));
-    }else{
-      assert( pPg->pPager==pPager );
-      if( pDataToFill ){
-        /* Just copy from the given memory */
-        memcpy(pPg->pData, pDataToFill, pPager->pageSize);
-        CODEC1(pPager, pPg->pData, pPg->pgno, 3, rc = SQLITE_NOMEM;
-                                                 goto pager_acquire_err);
-      }else{
-        /* Load from disk (old regular sqlite code path) */
-        rc = readDbPage(pPg);
-        if( rc!=SQLITE_OK ){
-          goto pager_acquire_err;
-        }
-      }
-    }
-#ifdef SQLITE_CHECK_PAGES
-    pPg->pageHash = pager_pagehash(pPg);
-#endif
-  }
-
-  return SQLITE_OK;
-
-pager_acquire_err:
-  assert( rc!=SQLITE_OK );
-  if( pPg ){
-    sqlite3PcacheDrop(pPg);
-  }
-  pagerUnlockIfUnused(pPager);
-
-  *ppPage = 0;
-  return rc;
-}
-
-/*
-** Acquire a page if it is already in the in-memory cache.  Do
-** not read the page from disk.  Return a pointer to the page,
-** or 0 if the page is not in cache. Also, return 0 if the 
-** pager is in PAGER_UNLOCK state when this function is called,
-** or if the pager is in an error state other than SQLITE_FULL.
-**
-** See also sqlite3PagerGet().  The difference between this routine
-** and sqlite3PagerGet() is that _get() will go to the disk and read
-** in the page if the page is not already in cache.  This routine
-** returns NULL if the page is not in cache or if a disk I/O error 
-** has ever happened.
-*/
-DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
-  PgHdr *pPg = 0;
-  assert( pPager!=0 );
-  assert( pgno!=0 );
-  assert( pPager->pPCache!=0 );
-  assert( pPager->state > PAGER_UNLOCK );
-  sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &pPg);
-  return pPg;
-}
-
-/*
-** Release a page reference.
-**
-** If the number of references to the page drop to zero, then the
-** page is added to the LRU list.  When all references to all pages
-** are released, a rollback occurs and the lock on the database is
-** removed.
-*/
-void sqlite3PagerUnref(DbPage *pPg){
-  if( pPg ){
-    Pager *pPager = pPg->pPager;
-    sqlite3PcacheRelease(pPg);
-    pagerUnlockIfUnused(pPager);
-  }
-}
-
-/*
-** If the main journal file has already been opened, ensure that the
-** sub-journal file is open too. If the main journal is not open,
-** this function is a no-op.
-**
-** SQLITE_OK is returned if everything goes according to plan. 
-** An SQLITE_IOERR_XXX error code is returned if a call to 
-** sqlite3OsOpen() fails.
-*/
-static int openSubJournal(Pager *pPager){
-  int rc = SQLITE_OK;
-  if( isOpen(pPager->jfd) && !isOpen(pPager->sjfd) ){
-    if( pPager->journalMode==PAGER_JOURNALMODE_MEMORY || pPager->subjInMemory ){
-      sqlite3MemJournalOpen(pPager->sjfd);
-    }else{
-      rc = pagerOpentemp(pPager, pPager->sjfd, SQLITE_OPEN_SUBJOURNAL);
-    }
-  }
-  return rc;
-}
-
-/*
-** This function is called at the start of every write transaction.
-** There must already be a RESERVED or EXCLUSIVE lock on the database 
-** file when this routine is called.
-**
-** Open the journal file for pager pPager and write a journal header
-** to the start of it. If there are active savepoints, open the sub-journal
-** as well. This function is only used when the journal file is being 
-** opened to write a rollback log for a transaction. It is not used 
-** when opening a hot journal file to roll it back.
-**
-** If the journal file is already open (as it may be in exclusive mode),
-** then this function just writes a journal header to the start of the
-** already open file. 
-**
-** Whether or not the journal file is opened by this function, the
-** Pager.pInJournal bitvec structure is allocated.
-**
-** Return SQLITE_OK if everything is successful. Otherwise, return 
-** SQLITE_NOMEM if the attempt to allocate Pager.pInJournal fails, or 
-** an IO error code if opening or writing the journal file fails.
-*/
-static int pager_open_journal(Pager *pPager){
-  int rc = SQLITE_OK;                        /* Return code */
-  sqlite3_vfs * const pVfs = pPager->pVfs;   /* Local cache of vfs pointer */
-
-  assert( pPager->state>=PAGER_RESERVED );
-  assert( pPager->useJournal );
-  assert( pPager->journalMode!=PAGER_JOURNALMODE_OFF );
-  assert( pPager->pInJournal==0 );
-  
-  /* If already in the error state, this function is a no-op.  But on
-  ** the other hand, this routine is never called if we are already in
-  ** an error state. */
-  if( NEVER(pPager->errCode) ) return pPager->errCode;
-
-  /* TODO: Is it really possible to get here with dbSizeValid==0? If not,
-  ** the call to PagerPagecount() can be removed.
-  */
-  testcase( pPager->dbSizeValid==0 );
-  sqlite3PagerPagecount(pPager, 0);
-
-  pPager->pInJournal = sqlite3BitvecCreate(pPager->dbSize);
-  if( pPager->pInJournal==0 ){
-    return SQLITE_NOMEM;
-  }
-
-  /* Open the journal file if it is not already open. */
-  if( !isOpen(pPager->jfd) ){
-    if( pPager->journalMode==PAGER_JOURNALMODE_MEMORY ){
-      sqlite3MemJournalOpen(pPager->jfd);
-    }else{
-      const int flags =                   /* VFS flags to open journal file */
-        SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|
-        (pPager->tempFile ? 
-          (SQLITE_OPEN_DELETEONCLOSE|SQLITE_OPEN_TEMP_JOURNAL):
-          (SQLITE_OPEN_MAIN_JOURNAL)
-        );
-#ifdef SQLITE_ENABLE_ATOMIC_WRITE
-      rc = sqlite3JournalOpen(
-          pVfs, pPager->zJournal, pPager->jfd, flags, jrnlBufferSize(pPager)
-      );
-#else
-      rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, flags, 0);
-#endif
-    }
-    assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
-  }
-
-
-  /* Write the first journal header to the journal file and open 
-  ** the sub-journal if necessary.
-  */
-  if( rc==SQLITE_OK ){
-    /* TODO: Check if all of these are really required. */
-    pPager->dbOrigSize = pPager->dbSize;
-    pPager->journalStarted = 0;
-    pPager->needSync = 0;
-    pPager->nRec = 0;
-    pPager->journalOff = 0;
-    pPager->setMaster = 0;
-    pPager->journalHdr = 0;
-    rc = writeJournalHdr(pPager);
-  }
-  if( rc==SQLITE_OK && pPager->nSavepoint ){
-    rc = openSubJournal(pPager);
-  }
-
-  if( rc!=SQLITE_OK ){
-    sqlite3BitvecDestroy(pPager->pInJournal);
-    pPager->pInJournal = 0;
-  }
-  return rc;
-}
-
-/*
-** Begin a write-transaction on the specified pager object. If a 
-** write-transaction has already been opened, this function is a no-op.
-**
-** If the exFlag argument is false, then acquire at least a RESERVED
-** lock on the database file. If exFlag is true, then acquire at least
-** an EXCLUSIVE lock. If such a lock is already held, no locking 
-** functions need be called.
-**
-** If this is not a temporary or in-memory file and, the journal file is 
-** opened if it has not been already. For a temporary file, the opening 
-** of the journal file is deferred until there is an actual need to 
-** write to the journal. TODO: Why handle temporary files differently?
-**
-** If the journal file is opened (or if it is already open), then a
-** journal-header is written to the start of it.
-**
-** If the subjInMemory argument is non-zero, then any sub-journal opened
-** within this transaction will be opened as an in-memory file. This
-** has no effect if the sub-journal is already opened (as it may be when
-** running in exclusive mode) or if the transaction does not require a
-** sub-journal. If the subjInMemory argument is zero, then any required
-** sub-journal is implemented in-memory if pPager is an in-memory database, 
-** or using a temporary file otherwise.
-*/
-int sqlite3PagerBegin(Pager *pPager, int exFlag, int subjInMemory){
-  int rc = SQLITE_OK;
-  assert( pPager->state!=PAGER_UNLOCK );
-  pPager->subjInMemory = (u8)subjInMemory;
-  if( pPager->state==PAGER_SHARED ){
-    assert( pPager->pInJournal==0 );
-    assert( !MEMDB && !pPager->tempFile );
-
-    /* Obtain a RESERVED lock on the database file. If the exFlag parameter
-    ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
-    ** busy-handler callback can be used when upgrading to the EXCLUSIVE
-    ** lock, but not when obtaining the RESERVED lock.
-    */
-    rc = sqlite3OsLock(pPager->fd, RESERVED_LOCK);
-    if( rc==SQLITE_OK ){
-      pPager->state = PAGER_RESERVED;
-      if( exFlag ){
-        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
-      }
-    }
-
-    /* If the required locks were successfully obtained, open the journal
-    ** file and write the first journal-header to it.
-    */
-    if( rc==SQLITE_OK && pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
-      rc = pager_open_journal(pPager);
-    }
-  }else if( isOpen(pPager->jfd) && pPager->journalOff==0 ){
-    /* This happens when the pager was in exclusive-access mode the last
-    ** time a (read or write) transaction was successfully concluded
-    ** by this connection. Instead of deleting the journal file it was 
-    ** kept open and either was truncated to 0 bytes or its header was
-    ** overwritten with zeros.
-    */
-    assert( pPager->nRec==0 );
-    assert( pPager->dbOrigSize==0 );
-    assert( pPager->pInJournal==0 );
-    rc = pager_open_journal(pPager);
-  }
-
-  PAGERTRACE(("TRANSACTION %d\n", PAGERID(pPager)));
-  assert( !isOpen(pPager->jfd) || pPager->journalOff>0 || rc!=SQLITE_OK );
-  if( rc!=SQLITE_OK ){
-    assert( !pPager->dbModified );
-    /* Ignore any IO error that occurs within pager_end_transaction(). The
-    ** purpose of this call is to reset the internal state of the pager
-    ** sub-system. It doesn't matter if the journal-file is not properly
-    ** finalized at this point (since it is not a valid journal file anyway).
-    */
-    pager_end_transaction(pPager, 0);
-  }
-  return rc;
-}
-
-/*
-** Mark a single data page as writeable. The page is written into the 
-** main journal or sub-journal as required. If the page is written into
-** one of the journals, the corresponding bit is set in the 
-** Pager.pInJournal bitvec and the PagerSavepoint.pInSavepoint bitvecs
-** of any open savepoints as appropriate.
-*/
-static int pager_write(PgHdr *pPg){
-  void *pData = pPg->pData;
-  Pager *pPager = pPg->pPager;
-  int rc = SQLITE_OK;
-
-  /* This routine is not called unless a transaction has already been
-  ** started.
-  */
-  assert( pPager->state>=PAGER_RESERVED );
-
-  /* If an error has been previously detected, we should not be
-  ** calling this routine.  Repeat the error for robustness.
-  */
-  if( NEVER(pPager->errCode) )  return pPager->errCode;
-
-  /* Higher-level routines never call this function if database is not
-  ** writable.  But check anyway, just for robustness. */
-  if( NEVER(pPager->readOnly) ) return SQLITE_PERM;
-
-  assert( !pPager->setMaster );
-
-  CHECK_PAGE(pPg);
-
-  /* Mark the page as dirty.  If the page has already been written
-  ** to the journal then we can return right away.
-  */
-  sqlite3PcacheMakeDirty(pPg);
-  if( pageInJournal(pPg) && !subjRequiresPage(pPg) ){
-    pPager->dbModified = 1;
-  }else{
-
-    /* If we get this far, it means that the page needs to be
-    ** written to the transaction journal or the ckeckpoint journal
-    ** or both.
-    **
-    ** Higher level routines should have already started a transaction,
-    ** which means they have acquired the necessary locks and opened
-    ** a rollback journal.  Double-check to makes sure this is the case.
-    */
-    rc = sqlite3PagerBegin(pPager, 0, pPager->subjInMemory);
-    if( NEVER(rc!=SQLITE_OK) ){
-      return rc;
-    }
-    if( !isOpen(pPager->jfd) && pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
-      assert( pPager->useJournal );
-      rc = pager_open_journal(pPager);
-      if( rc!=SQLITE_OK ) return rc;
-    }
-    pPager->dbModified = 1;
-  
-    /* The transaction journal now exists and we have a RESERVED or an
-    ** EXCLUSIVE lock on the main database file.  Write the current page to
-    ** the transaction journal if it is not there already.
-    */
-    if( !pageInJournal(pPg) && isOpen(pPager->jfd) ){
-      if( pPg->pgno<=pPager->dbOrigSize ){
-        u32 cksum;
-        char *pData2;
-
-        /* We should never write to the journal file the page that
-        ** contains the database locks.  The following assert verifies
-        ** that we do not. */
-        assert( pPg->pgno!=PAGER_MJ_PGNO(pPager) );
-        CODEC2(pPager, pData, pPg->pgno, 7, return SQLITE_NOMEM, pData2);
-        cksum = pager_cksum(pPager, (u8*)pData2);
-        rc = write32bits(pPager->jfd, pPager->journalOff, pPg->pgno);
-        if( rc==SQLITE_OK ){
-          rc = sqlite3OsWrite(pPager->jfd, pData2, pPager->pageSize,
-                              pPager->journalOff + 4);
-          pPager->journalOff += pPager->pageSize+4;
-        }
-        if( rc==SQLITE_OK ){
-          rc = write32bits(pPager->jfd, pPager->journalOff, cksum);
-          pPager->journalOff += 4;
-        }
-        IOTRACE(("JOUT %p %d %lld %d\n", pPager, pPg->pgno, 
-                 pPager->journalOff, pPager->pageSize));
-        PAGER_INCR(sqlite3_pager_writej_count);
-        PAGERTRACE(("JOURNAL %d page %d needSync=%d hash(%08x)\n",
-             PAGERID(pPager), pPg->pgno, 
-             ((pPg->flags&PGHDR_NEED_SYNC)?1:0), pager_pagehash(pPg)));
-
-        /* Even if an IO or diskfull error occurred while journalling the
-        ** page in the block above, set the need-sync flag for the page.
-        ** Otherwise, when the transaction is rolled back, the logic in
-        ** playback_one_page() will think that the page needs to be restored
-        ** in the database file. And if an IO error occurs while doing so,
-        ** then corruption may follow.
-        */
-        if( !pPager->noSync ){
-          pPg->flags |= PGHDR_NEED_SYNC;
-          pPager->needSync = 1;
-        }
-
-        /* An error has occurred writing to the journal file. The 
-        ** transaction will be rolled back by the layer above.
-        */
-        if( rc!=SQLITE_OK ){
-          return rc;
-        }
-
-        pPager->nRec++;
-        assert( pPager->pInJournal!=0 );
-        rc = sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);
-        testcase( rc==SQLITE_NOMEM );
-        assert( rc==SQLITE_OK || rc==SQLITE_NOMEM );
-        rc |= addToSavepointBitvecs(pPager, pPg->pgno);
-        if( rc!=SQLITE_OK ){
-          assert( rc==SQLITE_NOMEM );
-          return rc;
-        }
-      }else{
-        if( !pPager->journalStarted && !pPager->noSync ){
-          pPg->flags |= PGHDR_NEED_SYNC;
-          pPager->needSync = 1;
-        }
-        PAGERTRACE(("APPEND %d page %d needSync=%d\n",
-                PAGERID(pPager), pPg->pgno,
-               ((pPg->flags&PGHDR_NEED_SYNC)?1:0)));
-      }
-    }
-  
-    /* If the statement journal is open and the page is not in it,
-    ** then write the current page to the statement journal.  Note that
-    ** the statement journal format differs from the standard journal format
-    ** in that it omits the checksums and the header.
-    */
-    if( subjRequiresPage(pPg) ){
-      rc = subjournalPage(pPg);
-    }
-  }
-
-  /* Update the database size and return.
-  */
-  assert( pPager->state>=PAGER_SHARED );
-  if( pPager->dbSize<pPg->pgno ){
-    pPager->dbSize = pPg->pgno;
-  }
-  return rc;
-}
-
-/*
-** Mark a data page as writeable. This routine must be called before 
-** making changes to a page. The caller must check the return value 
-** of this function and be careful not to change any page data unless 
-** this routine returns SQLITE_OK.
-**
-** The difference between this function and pager_write() is that this
-** function also deals with the special case where 2 or more pages
-** fit on a single disk sector. In this case all co-resident pages
-** must have been written to the journal file before returning.
-**
-** If an error occurs, SQLITE_NOMEM or an IO error code is returned
-** as appropriate. Otherwise, SQLITE_OK.
-*/
-int sqlite3PagerWrite(DbPage *pDbPage){
-  int rc = SQLITE_OK;
-
-  PgHdr *pPg = pDbPage;
-  Pager *pPager = pPg->pPager;
-  Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);
-
-  if( nPagePerSector>1 ){
-    Pgno nPageCount;          /* Total number of pages in database file */
-    Pgno pg1;                 /* First page of the sector pPg is located on. */
-    int nPage;                /* Number of pages starting at pg1 to journal */
-    int ii;                   /* Loop counter */
-    int needSync = 0;         /* True if any page has PGHDR_NEED_SYNC */
-
-    /* Set the doNotSync flag to 1. This is because we cannot allow a journal
-    ** header to be written between the pages journaled by this function.
-    */
-    assert( !MEMDB );
-    assert( pPager->doNotSync==0 );
-    pPager->doNotSync = 1;
-
-    /* This trick assumes that both the page-size and sector-size are
-    ** an integer power of 2. It sets variable pg1 to the identifier
-    ** of the first page of the sector pPg is located on.
-    */
-    pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;
-
-    sqlite3PagerPagecount(pPager, (int *)&nPageCount);
-    if( pPg->pgno>nPageCount ){
-      nPage = (pPg->pgno - pg1)+1;
-    }else if( (pg1+nPagePerSector-1)>nPageCount ){
-      nPage = nPageCount+1-pg1;
-    }else{
-      nPage = nPagePerSector;
-    }
-    assert(nPage>0);
-    assert(pg1<=pPg->pgno);
-    assert((pg1+nPage)>pPg->pgno);
-
-    for(ii=0; ii<nPage && rc==SQLITE_OK; ii++){
-      Pgno pg = pg1+ii;
-      PgHdr *pPage;
-      if( pg==pPg->pgno || !sqlite3BitvecTest(pPager->pInJournal, pg) ){
-        if( pg!=PAGER_MJ_PGNO(pPager) ){
-          rc = sqlite3PagerGet(pPager, pg, &pPage);
-          if( rc==SQLITE_OK ){
-            rc = pager_write(pPage);
-            if( pPage->flags&PGHDR_NEED_SYNC ){
-              needSync = 1;
-              assert(pPager->needSync);
-            }
-            sqlite3PagerUnref(pPage);
-          }
-        }
-      }else if( (pPage = pager_lookup(pPager, pg))!=0 ){
-        if( pPage->flags&PGHDR_NEED_SYNC ){
-          needSync = 1;
-        }
-        sqlite3PagerUnref(pPage);
-      }
-    }
-
-    /* If the PGHDR_NEED_SYNC flag is set for any of the nPage pages 
-    ** starting at pg1, then it needs to be set for all of them. Because
-    ** writing to any of these nPage pages may damage the others, the
-    ** journal file must contain sync()ed copies of all of them
-    ** before any of them can be written out to the database file.
-    */
-    if( rc==SQLITE_OK && needSync ){
-      assert( !MEMDB && pPager->noSync==0 );
-      for(ii=0; ii<nPage; ii++){
-        PgHdr *pPage = pager_lookup(pPager, pg1+ii);
-        if( pPage ){
-          pPage->flags |= PGHDR_NEED_SYNC;
-          sqlite3PagerUnref(pPage);
-        }
-      }
-      assert(pPager->needSync);
-    }
-
-    assert( pPager->doNotSync==1 );
-    pPager->doNotSync = 0;
-  }else{
-    rc = pager_write(pDbPage);
-  }
-  return rc;
-}
-
-/*
-** Return TRUE if the page given in the argument was previously passed
-** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
-** to change the content of the page.
-*/
-#ifndef NDEBUG
-int sqlite3PagerIswriteable(DbPage *pPg){
-  return pPg->flags&PGHDR_DIRTY;
-}
-#endif
-
-/*
-** A call to this routine tells the pager that it is not necessary to
-** write the information on page pPg back to the disk, even though
-** that page might be marked as dirty.  This happens, for example, when
-** the page has been added as a leaf of the freelist and so its
-** content no longer matters.
-**
-** The overlying software layer calls this routine when all of the data
-** on the given page is unused. The pager marks the page as clean so
-** that it does not get written to disk.
-**
-** Tests show that this optimization can quadruple the speed of large 
-** DELETE operations.
-*/
-void sqlite3PagerDontWrite(PgHdr *pPg){
-  Pager *pPager = pPg->pPager;
-  if( (pPg->flags&PGHDR_DIRTY) && pPager->nSavepoint==0 ){
-    PAGERTRACE(("DONT_WRITE page %d of %d\n", pPg->pgno, PAGERID(pPager)));
-    IOTRACE(("CLEAN %p %d\n", pPager, pPg->pgno))
-    pPg->flags |= PGHDR_DONT_WRITE;
-#ifdef SQLITE_CHECK_PAGES
-    pPg->pageHash = pager_pagehash(pPg);
-#endif
-  }
-}
-
-/*
-** This routine is called to increment the value of the database file 
-** change-counter, stored as a 4-byte big-endian integer starting at 
-** byte offset 24 of the pager file.
-**
-** If the isDirectMode flag is zero, then this is done by calling 
-** sqlite3PagerWrite() on page 1, then modifying the contents of the
-** page data. In this case the file will be updated when the current
-** transaction is committed.
-**
-** The isDirectMode flag may only be non-zero if the library was compiled
-** with the SQLITE_ENABLE_ATOMIC_WRITE macro defined. In this case,
-** if isDirect is non-zero, then the database file is updated directly
-** by writing an updated version of page 1 using a call to the 
-** sqlite3OsWrite() function.
-*/
-static int pager_incr_changecounter(Pager *pPager, int isDirectMode){
-  int rc = SQLITE_OK;
-
-  /* Declare and initialize constant integer 'isDirect'. If the
-  ** atomic-write optimization is enabled in this build, then isDirect
-  ** is initialized to the value passed as the isDirectMode parameter
-  ** to this function. Otherwise, it is always set to zero.
-  **
-  ** The idea is that if the atomic-write optimization is not
-  ** enabled at compile time, the compiler can omit the tests of
-  ** 'isDirect' below, as well as the block enclosed in the
-  ** "if( isDirect )" condition.
-  */
-#ifndef SQLITE_ENABLE_ATOMIC_WRITE
-# define DIRECT_MODE 0
-  assert( isDirectMode==0 );
-  UNUSED_PARAMETER(isDirectMode);
-#else
-# define DIRECT_MODE isDirectMode
-#endif
-
-  assert( pPager->state>=PAGER_RESERVED );
-  if( !pPager->changeCountDone && ALWAYS(pPager->dbSize>0) ){
-    PgHdr *pPgHdr;                /* Reference to page 1 */
-    u32 change_counter;           /* Initial value of change-counter field */
-
-    assert( !pPager->tempFile && isOpen(pPager->fd) );
-
-    /* Open page 1 of the file for writing. */
-    rc = sqlite3PagerGet(pPager, 1, &pPgHdr);
-    assert( pPgHdr==0 || rc==SQLITE_OK );
-
-    /* If page one was fetched successfully, and this function is not
-    ** operating in direct-mode, make page 1 writable.  When not in 
-    ** direct mode, page 1 is always held in cache and hence the PagerGet()
-    ** above is always successful - hence the ALWAYS on rc==SQLITE_OK.
-    */
-    if( !DIRECT_MODE && ALWAYS(rc==SQLITE_OK) ){
-      rc = sqlite3PagerWrite(pPgHdr);
-    }
-
-    if( rc==SQLITE_OK ){
-      /* Increment the value just read and write it back to byte 24. */
-      change_counter = sqlite3Get4byte((u8*)pPager->dbFileVers);
-      change_counter++;
-      put32bits(((char*)pPgHdr->pData)+24, change_counter);
-
-      /* If running in direct mode, write the contents of page 1 to the file. */
-      if( DIRECT_MODE ){
-        const void *zBuf = pPgHdr->pData;
-        assert( pPager->dbFileSize>0 );
-        rc = sqlite3OsWrite(pPager->fd, zBuf, pPager->pageSize, 0);
-        if( rc==SQLITE_OK ){
-          pPager->changeCountDone = 1;
-        }
-      }else{
-        pPager->changeCountDone = 1;
-      }
-    }
-
-    /* Release the page reference. */
-    sqlite3PagerUnref(pPgHdr);
-  }
-  return rc;
-}
-
-/*
-** Sync the pager file to disk. This is a no-op for in-memory files
-** or pages with the Pager.noSync flag set.
-**
-** If successful, or called on a pager for which it is a no-op, this
-** function returns SQLITE_OK. Otherwise, an IO error code is returned.
-*/
-int sqlite3PagerSync(Pager *pPager){
-  int rc;                              /* Return code */
-  assert( !MEMDB );
-  if( pPager->noSync ){
-    rc = SQLITE_OK;
-  }else{
-    rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
-  }
-  return rc;
-}
-
-/*
-** Sync the database file for the pager pPager. zMaster points to the name
-** of a master journal file that should be written into the individual
-** journal file. zMaster may be NULL, which is interpreted as no master
-** journal (a single database transaction).
-**
-** This routine ensures that:
-**
-**   * The database file change-counter is updated,
-**   * the journal is synced (unless the atomic-write optimization is used),
-**   * all dirty pages are written to the database file, 
-**   * the database file is truncated (if required), and
-**   * the database file synced. 
-**
-** The only thing that remains to commit the transaction is to finalize 
-** (delete, truncate or zero the first part of) the journal file (or 
-** delete the master journal file if specified).
-**
-** Note that if zMaster==NULL, this does not overwrite a previous value
-** passed to an sqlite3PagerCommitPhaseOne() call.
-**
-** If the final parameter - noSync - is true, then the database file itself
-** is not synced. The caller must call sqlite3PagerSync() directly to
-** sync the database file before calling CommitPhaseTwo() to delete the
-** journal file in this case.
-*/
-int sqlite3PagerCommitPhaseOne(
-  Pager *pPager,                  /* Pager object */
-  const char *zMaster,            /* If not NULL, the master journal name */
-  int noSync                      /* True to omit the xSync on the db file */
-){
-  int rc = SQLITE_OK;             /* Return code */
-
-  /* The dbOrigSize is never set if journal_mode=OFF */
-  assert( pPager->journalMode!=PAGER_JOURNALMODE_OFF || pPager->dbOrigSize==0 );
-
-  /* If a prior error occurred, this routine should not be called.  ROLLBACK
-  ** is the appropriate response to an error, not COMMIT.  Guard against
-  ** coding errors by repeating the prior error. */
-  if( NEVER(pPager->errCode) ) return pPager->errCode;
-
-  PAGERTRACE(("DATABASE SYNC: File=%s zMaster=%s nSize=%d\n", 
-      pPager->zFilename, zMaster, pPager->dbSize));
-
-  if( MEMDB && pPager->dbModified ){
-    /* If this is an in-memory db, or no pages have been written to, or this
-    ** function has already been called, it is mostly a no-op.  However, any
-    ** backup in progress needs to be restarted.
-    */
-    sqlite3BackupRestart(pPager->pBackup);
-  }else if( pPager->state!=PAGER_SYNCED && pPager->dbModified ){
-
-    /* The following block updates the change-counter. Exactly how it
-    ** does this depends on whether or not the atomic-update optimization
-    ** was enabled at compile time, and if this transaction meets the 
-    ** runtime criteria to use the operation: 
-    **
-    **    * The file-system supports the atomic-write property for
-    **      blocks of size page-size, and 
-    **    * This commit is not part of a multi-file transaction, and
-    **    * Exactly one page has been modified and store in the journal file.
-    **
-    ** If the optimization was not enabled at compile time, then the
-    ** pager_incr_changecounter() function is called to update the change
-    ** counter in 'indirect-mode'. If the optimization is compiled in but
-    ** is not applicable to this transaction, call sqlite3JournalCreate()
-    ** to make sure the journal file has actually been created, then call
-    ** pager_incr_changecounter() to update the change-counter in indirect
-    ** mode. 
-    **
-    ** Otherwise, if the optimization is both enabled and applicable,
-    ** then call pager_incr_changecounter() to update the change-counter
-    ** in 'direct' mode. In this case the journal file will never be
-    ** created for this transaction.
-    */
-#ifdef SQLITE_ENABLE_ATOMIC_WRITE
-    PgHdr *pPg;
-    assert( isOpen(pPager->jfd) || pPager->journalMode==PAGER_JOURNALMODE_OFF );
-    if( !zMaster && isOpen(pPager->jfd) 
-     && pPager->journalOff==jrnlBufferSize(pPager) 
-     && pPager->dbSize>=pPager->dbFileSize
-     && (0==(pPg = sqlite3PcacheDirtyList(pPager->pPCache)) || 0==pPg->pDirty)
-    ){
-      /* Update the db file change counter via the direct-write method. The 
-      ** following call will modify the in-memory representation of page 1 
-      ** to include the updated change counter and then write page 1 
-      ** directly to the database file. Because of the atomic-write 
-      ** property of the host file-system, this is safe.
-      */
-      rc = pager_incr_changecounter(pPager, 1);
-    }else{
-      rc = sqlite3JournalCreate(pPager->jfd);
-      if( rc==SQLITE_OK ){
-        rc = pager_incr_changecounter(pPager, 0);
-      }
-    }
-#else
-    rc = pager_incr_changecounter(pPager, 0);
-#endif
-    if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
-
-    /* If this transaction has made the database smaller, then all pages
-    ** being discarded by the truncation must be written to the journal
-    ** file. This can only happen in auto-vacuum mode.
-    **
-    ** Before reading the pages with page numbers larger than the 
-    ** current value of Pager.dbSize, set dbSize back to the value
-    ** that it took at the start of the transaction. Otherwise, the
-    ** calls to sqlite3PagerGet() return zeroed pages instead of 
-    ** reading data from the database file.
-    **
-    ** When journal_mode==OFF the dbOrigSize is always zero, so this
-    ** block never runs if journal_mode=OFF.
-    */
-#ifndef SQLITE_OMIT_AUTOVACUUM
-    if( pPager->dbSize<pPager->dbOrigSize 
-     && ALWAYS(pPager->journalMode!=PAGER_JOURNALMODE_OFF)
-    ){
-      Pgno i;                                   /* Iterator variable */
-      const Pgno iSkip = PAGER_MJ_PGNO(pPager); /* Pending lock page */
-      const Pgno dbSize = pPager->dbSize;       /* Database image size */ 
-      pPager->dbSize = pPager->dbOrigSize;
-      for( i=dbSize+1; i<=pPager->dbOrigSize; i++ ){
-        if( !sqlite3BitvecTest(pPager->pInJournal, i) && i!=iSkip ){
-          PgHdr *pPage;             /* Page to journal */
-          rc = sqlite3PagerGet(pPager, i, &pPage);
-          if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
-          rc = sqlite3PagerWrite(pPage);
-          sqlite3PagerUnref(pPage);
-          if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
-        }
-      } 
-      pPager->dbSize = dbSize;
-    }
-#endif
-
-    /* Write the master journal name into the journal file. If a master 
-    ** journal file name has already been written to the journal file, 
-    ** or if zMaster is NULL (no master journal), then this call is a no-op.
-    */
-    rc = writeMasterJournal(pPager, zMaster);
-    if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
-
-    /* Sync the journal file. If the atomic-update optimization is being
-    ** used, this call will not create the journal file or perform any
-    ** real IO.
-    */
-    rc = syncJournal(pPager);
-    if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
-
-    /* Write all dirty pages to the database file. */
-    rc = pager_write_pagelist(sqlite3PcacheDirtyList(pPager->pPCache));
-    if( rc!=SQLITE_OK ){
-      assert( rc!=SQLITE_IOERR_BLOCKED );
-      goto commit_phase_one_exit;
-    }
-    sqlite3PcacheCleanAll(pPager->pPCache);
-
-    /* If the file on disk is not the same size as the database image,
-    ** then use pager_truncate to grow or shrink the file here.
-    */
-    if( pPager->dbSize!=pPager->dbFileSize ){
-      Pgno nNew = pPager->dbSize - (pPager->dbSize==PAGER_MJ_PGNO(pPager));
-      assert( pPager->state>=PAGER_EXCLUSIVE );
-      rc = pager_truncate(pPager, nNew);
-      if( rc!=SQLITE_OK ) goto commit_phase_one_exit;
-    }
-
-    /* Finally, sync the database file. */
-    if( !pPager->noSync && !noSync ){
-      rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
-    }
-    IOTRACE(("DBSYNC %p\n", pPager))
-
-    pPager->state = PAGER_SYNCED;
-  }
-
-commit_phase_one_exit:
-  return rc;
-}
-
-
-/*
-** When this function is called, the database file has been completely
-** updated to reflect the changes made by the current transaction and
-** synced to disk. The journal file still exists in the file-system 
-** though, and if a failure occurs at this point it will eventually
-** be used as a hot-journal and the current transaction rolled back.
-**
-** This function finalizes the journal file, either by deleting, 
-** truncating or partially zeroing it, so that it cannot be used 
-** for hot-journal rollback. Once this is done the transaction is
-** irrevocably committed.
-**
-** If an error occurs, an IO error code is returned and the pager
-** moves into the error state. Otherwise, SQLITE_OK is returned.
-*/
-int sqlite3PagerCommitPhaseTwo(Pager *pPager){
-  int rc = SQLITE_OK;                  /* Return code */
-
-  /* This routine should not be called if a prior error has occurred.
-  ** But if (due to a coding error elsewhere in the system) it does get
-  ** called, just return the same error code without doing anything. */
-  if( NEVER(pPager->errCode) ) return pPager->errCode;
-
-  /* This function should not be called if the pager is not in at least
-  ** PAGER_RESERVED state. And indeed SQLite never does this. But it is
-  ** nice to have this defensive test here anyway.
-  */
-  if( NEVER(pPager->state<PAGER_RESERVED) ) return SQLITE_ERROR;
-
-  /* An optimization. If the database was not actually modified during
-  ** this transaction, the pager is running in exclusive-mode and is
-  ** using persistent journals, then this function is a no-op.
-  **
-  ** The start of the journal file currently contains a single journal 
-  ** header with the nRec field set to 0. If such a journal is used as
-  ** a hot-journal during hot-journal rollback, 0 changes will be made
-  ** to the database file. So there is no need to zero the journal 
-  ** header. Since the pager is in exclusive mode, there is no need
-  ** to drop any locks either.
-  */
-  if( pPager->dbModified==0 && pPager->exclusiveMode 
-   && pPager->journalMode==PAGER_JOURNALMODE_PERSIST
-  ){
-    assert( pPager->journalOff==JOURNAL_HDR_SZ(pPager) );
-    return SQLITE_OK;
-  }
-
-  PAGERTRACE(("COMMIT %d\n", PAGERID(pPager)));
-  assert( pPager->state==PAGER_SYNCED || MEMDB || !pPager->dbModified );
-  rc = pager_end_transaction(pPager, pPager->setMaster);
-  return pager_error(pPager, rc);
-}
-
-/*
-** Rollback all changes. The database falls back to PAGER_SHARED mode.
-**
-** This function performs two tasks:
-**
-**   1) It rolls back the journal file, restoring all database file and 
-**      in-memory cache pages to the state they were in when the transaction
-**      was opened, and
-**   2) It finalizes the journal file, so that it is not used for hot
-**      rollback at any point in the future.
-**
-** subject to the following qualifications:
-**
-** * If the journal file is not yet open when this function is called,
-**   then only (2) is performed. In this case there is no journal file
-**   to roll back.
-**
-** * If in an error state other than SQLITE_FULL, then task (1) is 
-**   performed. If successful, task (2). Regardless of the outcome
-**   of either, the error state error code is returned to the caller
-**   (i.e. either SQLITE_IOERR or SQLITE_CORRUPT).
-**
-** * If the pager is in PAGER_RESERVED state, then attempt (1). Whether
-**   or not (1) is succussful, also attempt (2). If successful, return
-**   SQLITE_OK. Otherwise, enter the error state and return the first 
-**   error code encountered. 
-**
-**   In this case there is no chance that the database was written to. 
-**   So is safe to finalize the journal file even if the playback 
-**   (operation 1) failed. However the pager must enter the error state
-**   as the contents of the in-memory cache are now suspect.
-**
-** * Finally, if in PAGER_EXCLUSIVE state, then attempt (1). Only
-**   attempt (2) if (1) is successful. Return SQLITE_OK if successful,
-**   otherwise enter the error state and return the error code from the 
-**   failing operation.
-**
-**   In this case the database file may have been written to. So if the
-**   playback operation did not succeed it would not be safe to finalize
-**   the journal file. It needs to be left in the file-system so that
-**   some other process can use it to restore the database state (by
-**   hot-journal rollback).
-*/
-int sqlite3PagerRollback(Pager *pPager){
-  int rc = SQLITE_OK;                  /* Return code */
-  PAGERTRACE(("ROLLBACK %d\n", PAGERID(pPager)));
-  if( !pPager->dbModified || !isOpen(pPager->jfd) ){
-    rc = pager_end_transaction(pPager, pPager->setMaster);
-  }else if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
-    if( pPager->state>=PAGER_EXCLUSIVE ){
-      pager_playback(pPager, 0);
-    }
-    rc = pPager->errCode;
-  }else{
-    if( pPager->state==PAGER_RESERVED ){
-      int rc2;
-      rc = pager_playback(pPager, 0);
-      rc2 = pager_end_transaction(pPager, pPager->setMaster);
-      if( rc==SQLITE_OK ){
-        rc = rc2;
-      }
-    }else{
-      rc = pager_playback(pPager, 0);
-    }
-
-    if( !MEMDB ){
-      pPager->dbSizeValid = 0;
-    }
-
-    /* If an error occurs during a ROLLBACK, we can no longer trust the pager
-    ** cache. So call pager_error() on the way out to make any error 
-    ** persistent.
-    */
-    rc = pager_error(pPager, rc);
-  }
-  return rc;
-}
-
-/*
-** Return TRUE if the database file is opened read-only.  Return FALSE
-** if the database is (in theory) writable.
-*/
-u8 sqlite3PagerIsreadonly(Pager *pPager){
-  return pPager->readOnly;
-}
-
-/*
-** Return the number of references to the pager.
-*/
-int sqlite3PagerRefcount(Pager *pPager){
-  return sqlite3PcacheRefCount(pPager->pPCache);
-}
-
-/*
-** Return the number of references to the specified page.
-*/
-int sqlite3PagerPageRefcount(DbPage *pPage){
-  return sqlite3PcachePageRefcount(pPage);
-}
-
-#ifdef SQLITE_TEST
-/*
-** This routine is used for testing and analysis only.
-*/
-int *sqlite3PagerStats(Pager *pPager){
-  static int a[11];
-  a[0] = sqlite3PcacheRefCount(pPager->pPCache);
-  a[1] = sqlite3PcachePagecount(pPager->pPCache);
-  a[2] = sqlite3PcacheGetCachesize(pPager->pPCache);
-  a[3] = pPager->dbSizeValid ? (int) pPager->dbSize : -1;
-  a[4] = pPager->state;
-  a[5] = pPager->errCode;
-  a[6] = pPager->nHit;
-  a[7] = pPager->nMiss;
-  a[8] = 0;  /* Used to be pPager->nOvfl */
-  a[9] = pPager->nRead;
-  a[10] = pPager->nWrite;
-  return a;
-}
-#endif
-
-/*
-** Return true if this is an in-memory pager.
-*/
-int sqlite3PagerIsMemdb(Pager *pPager){
-  return MEMDB;
-}
-
-/*
-** Check that there are at least nSavepoint savepoints open. If there are
-** currently less than nSavepoints open, then open one or more savepoints
-** to make up the difference. If the number of savepoints is already
-** equal to nSavepoint, then this function is a no-op.
-**
-** If a memory allocation fails, SQLITE_NOMEM is returned. If an error 
-** occurs while opening the sub-journal file, then an IO error code is
-** returned. Otherwise, SQLITE_OK.
-*/
-int sqlite3PagerOpenSavepoint(Pager *pPager, int nSavepoint){
-  int rc = SQLITE_OK;                       /* Return code */
-  int nCurrent = pPager->nSavepoint;        /* Current number of savepoints */
-
-  if( nSavepoint>nCurrent && pPager->useJournal ){
-    int ii;                                 /* Iterator variable */
-    PagerSavepoint *aNew;                   /* New Pager.aSavepoint array */
-
-    /* Either there is no active journal or the sub-journal is open or 
-    ** the journal is always stored in memory */
-    assert( pPager->nSavepoint==0 || isOpen(pPager->sjfd) ||
-            pPager->journalMode==PAGER_JOURNALMODE_MEMORY );
-
-    /* Grow the Pager.aSavepoint array using realloc(). Return SQLITE_NOMEM
-    ** if the allocation fails. Otherwise, zero the new portion in case a 
-    ** malloc failure occurs while populating it in the for(...) loop below.
-    */
-    aNew = (PagerSavepoint *)sqlite3Realloc(
-        pPager->aSavepoint, sizeof(PagerSavepoint)*nSavepoint
-    );
-    if( !aNew ){
-      return SQLITE_NOMEM;
-    }
-    memset(&aNew[nCurrent], 0, (nSavepoint-nCurrent) * sizeof(PagerSavepoint));
-    pPager->aSavepoint = aNew;
-    pPager->nSavepoint = nSavepoint;
-
-    /* Populate the PagerSavepoint structures just allocated. */
-    for(ii=nCurrent; ii<nSavepoint; ii++){
-      assert( pPager->dbSizeValid );
-      aNew[ii].nOrig = pPager->dbSize;
-      if( isOpen(pPager->jfd) && ALWAYS(pPager->journalOff>0) ){
-        aNew[ii].iOffset = pPager->journalOff;
-      }else{
-        aNew[ii].iOffset = JOURNAL_HDR_SZ(pPager);
-      }
-      aNew[ii].iSubRec = pPager->nSubRec;
-      aNew[ii].pInSavepoint = sqlite3BitvecCreate(pPager->dbSize);
-      if( !aNew[ii].pInSavepoint ){
-        return SQLITE_NOMEM;
-      }
-    }
-
-    /* Open the sub-journal, if it is not already opened. */
-    rc = openSubJournal(pPager);
-    assertTruncateConstraint(pPager);
-  }
-
-  return rc;
-}
-
-/*
-** This function is called to rollback or release (commit) a savepoint.
-** The savepoint to release or rollback need not be the most recently 
-** created savepoint.
-**
-** Parameter op is always either SAVEPOINT_ROLLBACK or SAVEPOINT_RELEASE.
-** If it is SAVEPOINT_RELEASE, then release and destroy the savepoint with
-** index iSavepoint. If it is SAVEPOINT_ROLLBACK, then rollback all changes
-** that have occurred since the specified savepoint was created.
-**
-** The savepoint to rollback or release is identified by parameter 
-** iSavepoint. A value of 0 means to operate on the outermost savepoint
-** (the first created). A value of (Pager.nSavepoint-1) means operate
-** on the most recently created savepoint. If iSavepoint is greater than
-** (Pager.nSavepoint-1), then this function is a no-op.
-**
-** If a negative value is passed to this function, then the current
-** transaction is rolled back. This is different to calling 
-** sqlite3PagerRollback() because this function does not terminate
-** the transaction or unlock the database, it just restores the 
-** contents of the database to its original state. 
-**
-** In any case, all savepoints with an index greater than iSavepoint 
-** are destroyed. If this is a release operation (op==SAVEPOINT_RELEASE),
-** then savepoint iSavepoint is also destroyed.
-**
-** This function may return SQLITE_NOMEM if a memory allocation fails,
-** or an IO error code if an IO error occurs while rolling back a 
-** savepoint. If no errors occur, SQLITE_OK is returned.
-*/ 
-int sqlite3PagerSavepoint(Pager *pPager, int op, int iSavepoint){
-  int rc = SQLITE_OK;
-
-  assert( op==SAVEPOINT_RELEASE || op==SAVEPOINT_ROLLBACK );
-  assert( iSavepoint>=0 || op==SAVEPOINT_ROLLBACK );
-
-  if( iSavepoint<pPager->nSavepoint ){
-    int ii;            /* Iterator variable */
-    int nNew;          /* Number of remaining savepoints after this op. */
-
-    /* Figure out how many savepoints will still be active after this
-    ** operation. Store this value in nNew. Then free resources associated 
-    ** with any savepoints that are destroyed by this operation.
-    */
-    nNew = iSavepoint + (op==SAVEPOINT_ROLLBACK);
-    for(ii=nNew; ii<pPager->nSavepoint; ii++){
-      sqlite3BitvecDestroy(pPager->aSavepoint[ii].pInSavepoint);
-    }
-    pPager->nSavepoint = nNew;
-
-    /* If this is a rollback operation, playback the specified savepoint.
-    ** If this is a temp-file, it is possible that the journal file has
-    ** not yet been opened. In this case there have been no changes to
-    ** the database file, so the playback operation can be skipped.
-    */
-    if( op==SAVEPOINT_ROLLBACK && isOpen(pPager->jfd) ){
-      PagerSavepoint *pSavepoint = (nNew==0)?0:&pPager->aSavepoint[nNew-1];
-      rc = pagerPlaybackSavepoint(pPager, pSavepoint);
-      assert(rc!=SQLITE_DONE);
-    }
-  
-    /* If this is a release of the outermost savepoint, truncate 
-    ** the sub-journal to zero bytes in size. */
-    if( nNew==0 && op==SAVEPOINT_RELEASE && isOpen(pPager->sjfd) ){
-      assert( rc==SQLITE_OK );
-      rc = sqlite3OsTruncate(pPager->sjfd, 0);
-      pPager->nSubRec = 0;
-    }
-  }
-  return rc;
-}
-
-/*
-** Return the full pathname of the database file.
-*/
-const char *sqlite3PagerFilename(Pager *pPager){
-  return pPager->zFilename;
-}
-
-/*
-** Return the VFS structure for the pager.
-*/
-const sqlite3_vfs *sqlite3PagerVfs(Pager *pPager){
-  return pPager->pVfs;
-}
-
-/*
-** Return the file handle for the database file associated
-** with the pager.  This might return NULL if the file has
-** not yet been opened.
-*/
-sqlite3_file *sqlite3PagerFile(Pager *pPager){
-  return pPager->fd;
-}
-
-/*
-** Return the full pathname of the journal file.
-*/
-const char *sqlite3PagerJournalname(Pager *pPager){
-  return pPager->zJournal;
-}
-
-/*
-** Return true if fsync() calls are disabled for this pager.  Return FALSE
-** if fsync()s are executed normally.
-*/
-int sqlite3PagerNosync(Pager *pPager){
-  return pPager->noSync;
-}
-
-#ifdef SQLITE_HAS_CODEC
-/*
-** Set or retrieve the codec for this pager
-*/
-static void sqlite3PagerSetCodec(
-  Pager *pPager,
-  void *(*xCodec)(void*,void*,Pgno,int),
-  void (*xCodecSizeChng)(void*,int,int),
-  void (*xCodecFree)(void*),
-  void *pCodec
-){
-  if( pPager->xCodecFree ) pPager->xCodecFree(pPager->pCodec);
-  pPager->xCodec = xCodec;
-  pPager->xCodecSizeChng = xCodecSizeChng;
-  pPager->xCodecFree = xCodecFree;
-  pPager->pCodec = pCodec;
-  pagerReportSize(pPager);
-}
-static void *sqlite3PagerGetCodec(Pager *pPager){
-  return pPager->pCodec;
-}
-#endif
-
-#ifndef SQLITE_OMIT_AUTOVACUUM
-/*
-** Move the page pPg to location pgno in the file.
-**
-** There must be no references to the page previously located at
-** pgno (which we call pPgOld) though that page is allowed to be
-** in cache.  If the page previously located at pgno is not already
-** in the rollback journal, it is not put there by by this routine.
-**
-** References to the page pPg remain valid. Updating any
-** meta-data associated with pPg (i.e. data stored in the nExtra bytes
-** allocated along with the page) is the responsibility of the caller.
-**
-** A transaction must be active when this routine is called. It used to be
-** required that a statement transaction was not active, but this restriction
-** has been removed (CREATE INDEX needs to move a page when a statement
-** transaction is active).
-**
-** If the fourth argument, isCommit, is non-zero, then this page is being
-** moved as part of a database reorganization just before the transaction 
-** is being committed. In this case, it is guaranteed that the database page 
-** pPg refers to will not be written to again within this transaction.
-**
-** This function may return SQLITE_NOMEM or an IO error code if an error
-** occurs. Otherwise, it returns SQLITE_OK.
-*/
-int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno, int isCommit){
-  PgHdr *pPgOld;               /* The page being overwritten. */
-  Pgno needSyncPgno = 0;       /* Old value of pPg->pgno, if sync is required */
-  int rc;                      /* Return code */
-  Pgno origPgno;               /* The original page number */
-
-  assert( pPg->nRef>0 );
-
-  /* If the page being moved is dirty and has not been saved by the latest
-  ** savepoint, then save the current contents of the page into the 
-  ** sub-journal now. This is required to handle the following scenario:
-  **
-  **   BEGIN;
-  **     <journal page X, then modify it in memory>
-  **     SAVEPOINT one;
-  **       <Move page X to location Y>
-  **     ROLLBACK TO one;
-  **
-  ** If page X were not written to the sub-journal here, it would not
-  ** be possible to restore its contents when the "ROLLBACK TO one"
-  ** statement were is processed.
-  **
-  ** subjournalPage() may need to allocate space to store pPg->pgno into
-  ** one or more savepoint bitvecs. This is the reason this function
-  ** may return SQLITE_NOMEM.
-  */
-  if( pPg->flags&PGHDR_DIRTY 
-   && subjRequiresPage(pPg)
-   && SQLITE_OK!=(rc = subjournalPage(pPg))
-  ){
-    return rc;
-  }
-
-  PAGERTRACE(("MOVE %d page %d (needSync=%d) moves to %d\n", 
-      PAGERID(pPager), pPg->pgno, (pPg->flags&PGHDR_NEED_SYNC)?1:0, pgno));
-  IOTRACE(("MOVE %p %d %d\n", pPager, pPg->pgno, pgno))
-
-  /* If the journal needs to be sync()ed before page pPg->pgno can
-  ** be written to, store pPg->pgno in local variable needSyncPgno.
-  **
-  ** If the isCommit flag is set, there is no need to remember that
-  ** the journal needs to be sync()ed before database page pPg->pgno 
-  ** can be written to. The caller has already promised not to write to it.
-  */
-  if( (pPg->flags&PGHDR_NEED_SYNC) && !isCommit ){
-    needSyncPgno = pPg->pgno;
-    assert( pageInJournal(pPg) || pPg->pgno>pPager->dbOrigSize );
-    assert( pPg->flags&PGHDR_DIRTY );
-    assert( pPager->needSync );
-  }
-
-  /* If the cache contains a page with page-number pgno, remove it
-  ** from its hash chain. Also, if the PgHdr.needSync was set for 
-  ** page pgno before the 'move' operation, it needs to be retained 
-  ** for the page moved there.
-  */
-  pPg->flags &= ~PGHDR_NEED_SYNC;
-  pPgOld = pager_lookup(pPager, pgno);
-  assert( !pPgOld || pPgOld->nRef==1 );
-  if( pPgOld ){
-    pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
-    sqlite3PcacheDrop(pPgOld);
-  }
-
-  origPgno = pPg->pgno;
-  sqlite3PcacheMove(pPg, pgno);
-  sqlite3PcacheMakeDirty(pPg);
-  pPager->dbModified = 1;
-
-  if( needSyncPgno ){
-    /* If needSyncPgno is non-zero, then the journal file needs to be 
-    ** sync()ed before any data is written to database file page needSyncPgno.
-    ** Currently, no such page exists in the page-cache and the 
-    ** "is journaled" bitvec flag has been set. This needs to be remedied by
-    ** loading the page into the pager-cache and setting the PgHdr.needSync 
-    ** flag.
-    **
-    ** If the attempt to load the page into the page-cache fails, (due
-    ** to a malloc() or IO failure), clear the bit in the pInJournal[]
-    ** array. Otherwise, if the page is loaded and written again in
-    ** this transaction, it may be written to the database file before
-    ** it is synced into the journal file. This way, it may end up in
-    ** the journal file twice, but that is not a problem.
-    **
-    ** The sqlite3PagerGet() call may cause the journal to sync. So make
-    ** sure the Pager.needSync flag is set too.
-    */
-    PgHdr *pPgHdr;
-    assert( pPager->needSync );
-    rc = sqlite3PagerGet(pPager, needSyncPgno, &pPgHdr);
-    if( rc!=SQLITE_OK ){
-      if( needSyncPgno<=pPager->dbOrigSize ){
-        assert( pPager->pTmpSpace!=0 );
-        sqlite3BitvecClear(pPager->pInJournal, needSyncPgno, pPager->pTmpSpace);
-      }
-      return rc;
-    }
-    pPager->needSync = 1;
-    assert( pPager->noSync==0 && !MEMDB );
-    pPgHdr->flags |= PGHDR_NEED_SYNC;
-    sqlite3PcacheMakeDirty(pPgHdr);
-    sqlite3PagerUnref(pPgHdr);
-  }
-
-  /*
-  ** For an in-memory database, make sure the original page continues
-  ** to exist, in case the transaction needs to roll back.  We allocate
-  ** the page now, instead of at rollback, because we can better deal
-  ** with an out-of-memory error now.  Ticket #3761.
-  */
-  if( MEMDB ){
-    DbPage *pNew;
-    rc = sqlite3PagerAcquire(pPager, origPgno, &pNew, 1);
-    if( rc!=SQLITE_OK ){
-      sqlite3PcacheMove(pPg, origPgno);
-      return rc;
-    }
-    sqlite3PagerUnref(pNew);
-  }
-
-  return SQLITE_OK;
-}
-#endif
-
-/* Begin preload-cache.patch for Chromium */
-/**
-** When making large allocations, there is no need to stress the heap and
-** potentially hold its lock while we allocate a bunch of memory.  If we know
-** the allocation will be large, go directly to the OS instead of the heap.
-**/
-static void* allocLarge(size_t size) {
-#if SQLITE_OS_WIN
-  return VirtualAlloc(NULL, size, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
-#else
-  return sqlite3Malloc(size);
-#endif
-}
-
-static void freeLarge(void* ptr) {
-#if SQLITE_OS_WIN
-  VirtualFree(ptr, 0, MEM_RELEASE);
-#else
-  sqlite3_free(ptr);
-#endif
-}
-
-/**
-** Addition: This will attempt to populate the database cache with
-** the first N bytes of the file, where N is the total size of the cache.
-** Because we can load this as one chunk from the disk, this is much faster
-** than loading a subset of the pages one at a time in random order.
-**
-** The pager must be initialized before this function is called. This means a
-* statement must be open that has initialized the pager and is keeping the
-** cache in memory.
-**/
-int sqlite3PagerLoadall(Pager* pPager)
-{
-  int i;
-  int rc;
-  int nMax;
-  int loadSize;
-  int loadPages;
-  unsigned char *fileData;
-
-  if (pPager->dbSize < 0 || pPager->pageSize < 0) {
-    /* pager not initialized, this means a statement is not open */
-    return SQLITE_MISUSE;
-  }
-
-  /* compute sizes */
-  nMax = sqlite3PcacheGetCachesize(pPager->pPCache);
-  if (nMax < pPager->dbSize)
-    loadPages = nMax;
-  else
-    loadPages = pPager->dbSize;
-  loadSize = loadPages * pPager->pageSize;
-
-  /* load the file as one chunk */
-  fileData = allocLarge(loadSize);
-  if (! fileData)
-    return SQLITE_NOMEM;
-  rc = sqlite3OsRead(pPager->fd, fileData, loadSize, 0);
-  if (rc != SQLITE_OK) {
-    freeLarge(fileData);
-    return rc;
-  }
-
-  /* Copy the data to each page. Note that the page numbers we pass to _get
-   * are one-based, 0 is a marker for no page. We also need to check that we
-   * haven't loaded more pages than the cache can hold total. There may have
-   * already been a few pages loaded before, so we may fill the cache before
-   * loading all of the pages we want to.
-   */
-  for(i=1;
-      i <= loadPages && sqlite3PcachePagecount(pPager->pPCache) < nMax;
-      i++) {
-    DbPage *pPage = 0;
-    rc = sqlite3PagerAcquire2(pPager, i, &pPage, 0,
-                              &fileData[(i-1)*(i64)pPager->pageSize]);
-    if (rc != SQLITE_OK)
-      break;
-    sqlite3PagerUnref(pPage);
-  }
-  freeLarge(fileData);
-  return SQLITE_OK;
-}
-/* End preload-cache.patch for Chromium */
-
-/*
-** Return a pointer to the data for the specified page.
-*/
-void *sqlite3PagerGetData(DbPage *pPg){
-  assert( pPg->nRef>0 || pPg->pPager->memDb );
-  return pPg->pData;
-}
-
-/*
-** Return a pointer to the Pager.nExtra bytes of "extra" space 
-** allocated along with the specified page.
-*/
-void *sqlite3PagerGetExtra(DbPage *pPg){
-  return pPg->pExtra;
-}
-
-/*
-** Get/set the locking-mode for this pager. Parameter eMode must be one
-** of PAGER_LOCKINGMODE_QUERY, PAGER_LOCKINGMODE_NORMAL or 
-** PAGER_LOCKINGMODE_EXCLUSIVE. If the parameter is not _QUERY, then
-** the locking-mode is set to the value specified.
-**
-** The returned value is either PAGER_LOCKINGMODE_NORMAL or
-** PAGER_LOCKINGMODE_EXCLUSIVE, indicating the current (possibly updated)
-** locking-mode.
-*/
-int sqlite3PagerLockingMode(Pager *pPager, int eMode){
-  assert( eMode==PAGER_LOCKINGMODE_QUERY
-            || eMode==PAGER_LOCKINGMODE_NORMAL
-            || eMode==PAGER_LOCKINGMODE_EXCLUSIVE );
-  assert( PAGER_LOCKINGMODE_QUERY<0 );
-  assert( PAGER_LOCKINGMODE_NORMAL>=0 && PAGER_LOCKINGMODE_EXCLUSIVE>=0 );
-  if( eMode>=0 && !pPager->tempFile ){
-    pPager->exclusiveMode = (u8)eMode;
-  }
-  return (int)pPager->exclusiveMode;
-}
-
-/*
-** Get/set the journal-mode for this pager. Parameter eMode must be one of:
-**
-**    PAGER_JOURNALMODE_QUERY
-**    PAGER_JOURNALMODE_DELETE
-**    PAGER_JOURNALMODE_TRUNCATE
-**    PAGER_JOURNALMODE_PERSIST
-**    PAGER_JOURNALMODE_OFF
-**    PAGER_JOURNALMODE_MEMORY
-**
-** If the parameter is not _QUERY, then the journal_mode is set to the
-** value specified if the change is allowed.  The change is disallowed
-** for the following reasons:
-**
-**   *  An in-memory database can only have its journal_mode set to _OFF
-**      or _MEMORY.
-**
-**   *  The journal mode may not be changed while a transaction is active.
-**
-** The returned indicate the current (possibly updated) journal-mode.
-*/
-int sqlite3PagerJournalMode(Pager *pPager, int eMode){
-  assert( eMode==PAGER_JOURNALMODE_QUERY
-            || eMode==PAGER_JOURNALMODE_DELETE
-            || eMode==PAGER_JOURNALMODE_TRUNCATE
-            || eMode==PAGER_JOURNALMODE_PERSIST
-            || eMode==PAGER_JOURNALMODE_OFF 
-            || eMode==PAGER_JOURNALMODE_MEMORY );
-  assert( PAGER_JOURNALMODE_QUERY<0 );
-  if( eMode>=0
-   && (!MEMDB || eMode==PAGER_JOURNALMODE_MEMORY 
-              || eMode==PAGER_JOURNALMODE_OFF)
-   && !pPager->dbModified
-   && (!isOpen(pPager->jfd) || 0==pPager->journalOff)
-  ){
-    if( isOpen(pPager->jfd) ){
-      sqlite3OsClose(pPager->jfd);
-    }
-    pPager->journalMode = (u8)eMode;
-  }
-  return (int)pPager->journalMode;
-}
-
-/*
-** Get/set the size-limit used for persistent journal files.
-**
-** Setting the size limit to -1 means no limit is enforced.
-** An attempt to set a limit smaller than -1 is a no-op.
-*/
-i64 sqlite3PagerJournalSizeLimit(Pager *pPager, i64 iLimit){
-  if( iLimit>=-1 ){
-    pPager->journalSizeLimit = iLimit;
-  }
-  return pPager->journalSizeLimit;
-}
-
-/*
-** Return a pointer to the pPager->pBackup variable. The backup module
-** in backup.c maintains the content of this variable. This module
-** uses it opaquely as an argument to sqlite3BackupRestart() and
-** sqlite3BackupUpdate() only.
-*/
-sqlite3_backup **sqlite3PagerBackupPtr(Pager *pPager){
-  return &pPager->pBackup;
-}
-
-#endif /* SQLITE_OMIT_DISKIO */