FCL/sf/os/persistentdata: comparison persistentstorage/sqlite3api/SQLite/pager.c

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--1:000000000000
+:08ec8eefde2f
+/*
+** 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 1.496 2008/09/29 11:49:48 danielk1977 Exp $
+*/
+#ifndef SQLITE_OMIT_DISKIO
+#include "sqliteInt.h"
+/*
+** Macros for troubleshooting.  Normally turned off
+*/
+#if 0
+#define sqlite3DebugPrintf printf
+#define PAGERTRACE1(X)       sqlite3DebugPrintf(X)
+#define PAGERTRACE2(X,Y)     sqlite3DebugPrintf(X,Y)
+#define PAGERTRACE3(X,Y,Z)   sqlite3DebugPrintf(X,Y,Z)
+#define PAGERTRACE4(X,Y,Z,W) sqlite3DebugPrintf(X,Y,Z,W)
+#define PAGERTRACE5(X,Y,Z,W,V) sqlite3DebugPrintf(X,Y,Z,W,V)
+#else
+#define PAGERTRACE1(X)
+#define PAGERTRACE2(X,Y)
+#define PAGERTRACE3(X,Y,Z)
+#define PAGERTRACE4(X,Y,Z,W)
+#define PAGERTRACE5(X,Y,Z,W,V)
+#endif
+/*
+** The following two macros are used within the PAGERTRACEX() 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
+/*
+** If the SQLITE_BUSY_RESERVED_LOCK macro is set to true at compile-time,
+** then failed attempts to get a reserved lock will invoke the busy callback.
+** This is off by default.  To see why, consider the following scenario:
+**
+** Suppose thread A already has a shared lock and wants a reserved lock.
+** Thread B already has a reserved lock and wants an exclusive lock.  If
+** both threads are using their busy callbacks, it might be a long time
+** be for one of the threads give up and allows the other to proceed.
+** But if the thread trying to get the reserved lock gives up quickly
+** (if it never invokes its busy callback) then the contention will be
+** resolved quickly.
+*/
+#ifndef SQLITE_BUSY_RESERVED_LOCK
+# define SQLITE_BUSY_RESERVED_LOCK 0
+#endif
+/*
+** This macro rounds values up so that if the value is an address it
+** is guaranteed to be an address that is aligned to an 8-byte boundary.
+*/
+#define FORCE_ALIGNMENT(X)   (((X)+7)&~7)
+/*
+** A macro used for invoking the codec if there is one
+*/
+#ifdef SQLITE_HAS_CODEC
+# define CODEC1(P,D,N,X) if( P->xCodec!=0 ){ P->xCodec(P->pCodecArg,D,N,X); }
+# define CODEC2(P,D,N,X) ((char*)(P->xCodec!=0?P->xCodec(P->pCodecArg,D,N,X):D))
+#else
+# define CODEC1(P,D,N,X) /* NO-OP */
+# define CODEC2(P,D,N,X) ((char*)D)
+#endif
+/*
+** A open page cache is an instance of the following structure.
+**
+** 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.
+*/
+struct Pager {
+sqlite3_vfs *pVfs;          /* OS functions to use for IO */
+u8 journalOpen;             /* True if journal file descriptors is valid */
+u8 journalStarted;          /* True if header of journal is synced */
+u8 useJournal;              /* Use a rollback journal on this file */
+u8 noReadlock;              /* Do not bother to obtain readlocks */
+u8 stmtOpen;                /* True if the statement subjournal is open */
+u8 stmtInUse;               /* True we are in a statement subtransaction */
+u8 stmtAutoopen;            /* Open stmt journal when main journal is opened*/
+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 state;                   /* PAGER_UNLOCK, _SHARED, _RESERVED, etc. */
+u8 tempFile;                /* zFilename is a temporary file */
+u8 readOnly;                /* True for a read-only database */
+u8 needSync;                /* True if an fsync() is needed on the journal */
+u8 dirtyCache;              /* True if cached pages have changed */
+u8 alwaysRollback;          /* Disable DontRollback() for all pages */
+u8 memDb;                   /* True to inhibit all file I/O */
+u8 setMaster;               /* True if a m-j name has been written to jrnl */
+u8 doNotSync;               /* Boolean. While true, do not spill the cache */
+u8 exclusiveMode;           /* Boolean. True if locking_mode==EXCLUSIVE */
+u8 journalMode;             /* On of the PAGER_JOURNALMODE_* values */
+u8 dbModified;              /* True if there are any changes to the Db */
+u8 changeCountDone;         /* Set after incrementing the change-counter */
+u32 vfsFlags;               /* Flags for sqlite3_vfs.xOpen() */
+int errCode;                /* One of several kinds of errors */
+int dbSize;                 /* Number of pages in the file */
+int origDbSize;             /* dbSize before the current change */
+int stmtSize;               /* Size of database (in pages) at stmt_begin() */
+int nRec;                   /* Number of pages written to the journal */
+u32 cksumInit;              /* Quasi-random value added to every checksum */
+int stmtNRec;               /* Number of records in stmt subjournal */
+int nExtra;                 /* Add this many bytes to each in-memory page */
+int pageSize;               /* Number of bytes in a page */
+int nPage;                  /* Total number of in-memory pages */
+int mxPage;                 /* Maximum number of pages to hold in cache */
+Pgno mxPgno;                /* Maximum allowed size of the database */
+Bitvec *pInJournal;         /* One bit for each page in the database file */
+Bitvec *pInStmt;            /* One bit for each page in the database */
+Bitvec *pAlwaysRollback;    /* One bit for each page marked always-rollback */
+char *zFilename;            /* Name of the database file */
+char *zJournal;             /* Name of the journal file */
+char *zDirectory;           /* Directory hold database and journal files */
+sqlite3_file *fd, *jfd;     /* File descriptors for database and journal */
+sqlite3_file *stfd;         /* File descriptor for the statement subjournal*/
+BusyHandler *pBusyHandler;  /* Pointer to sqlite.busyHandler */
+i64 journalOff;             /* Current byte offset in the journal file */
+i64 journalHdr;             /* Byte offset to previous journal header */
+i64 stmtHdrOff;             /* First journal header written this statement */
+i64 stmtCksum;              /* cksumInit when statement was started */
+i64 stmtJSize;              /* Size of journal at stmt_begin() */
+int sectorSize;             /* Assumed sector size during rollback */
+#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 *pCodecArg;            /* First argument to xCodec() */
+#endif
+char *pTmpSpace;            /* Pager.pageSize bytes of space for tmp use */
+char dbFileVers[16];        /* Changes whenever database file changes */
+i64 journalSizeLimit;       /* Size limit for persistent journal files */
+PCache *pPCache;            /* Pointer to page cache object */
+};
+/*
+** 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 begin
+** 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 header and of each page in the journal is determined
+** by the following macros.
+*/
+#define JOURNAL_PG_SZ(pPager)  ((pPager->pageSize) + 8)
+/*
+** The journal header size for this pager. In the future, this could be
+** set to some value read from the disk controller. The important
+** characteristic is that it is the same size as a disk sector.
+*/
+#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
+/*
+** Page number PAGER_MJ_PGNO is never used in an SQLite database (it is
+** reserved for working around a windows/posix incompatibility). It is
+** used in the journal to signify that the remainder of the journal file
+** is devoted to storing a master journal name - there are no more pages to
+** roll back. See comments for function writeMasterJournal() for details.
+*/
+/* #define PAGER_MJ_PGNO(x) (PENDING_BYTE/((x)->pageSize)) */
+#define PAGER_MJ_PGNO(x) ((PENDING_BYTE/((x)->pageSize))+1)
+/*
+** The maximum legal page number is (2^31 - 1).
+*/
+#define PAGER_MAX_PGNO 2147483647
+/*
+** Return true if page *pPg has already been written to the statement
+** journal (or statement snapshot has been created, if *pPg is part
+** of an in-memory database).
+*/
+static int pageInStatement(PgHdr *pPg){
+Pager *pPager = pPg->pPager;
+if( MEMDB ){
+return pPg->apSave[1]!=0;
+}else{
+return sqlite3BitvecTest(pPager->pInStmt, 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);
+}
+/*
+** If file pFd is open, call sqlite3OsUnlock() on it.
+*/
+static int osUnlock(sqlite3_file *pFd, int eLock){
+if( !pFd->pMethods ){
+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.
+**
+** 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){
+int dc;           /* Device characteristics */
+int nSector;      /* Sector size */
+int szPage;        /* Page size */
+sqlite3_file *fd = pPager->fd;
+if( fd->pMethods ){
+dc = sqlite3OsDeviceCharacteristics(fd);
+nSector = sqlite3OsSectorSize(fd);
+szPage = pPager->pageSize;
+}
+assert(SQLITE_IOCAP_ATOMIC512==(512>>8));
+assert(SQLITE_IOCAP_ATOMIC64K==(65536>>8));
+if( !fd->pMethods ||
+(dc & (SQLITE_IOCAP_ATOMIC|(szPage>>8)) && nSector<=szPage) ){
+return JOURNAL_HDR_SZ(pPager) + JOURNAL_PG_SZ(pPager);
+}
+return 0;
+}
+#endif
+/*
+** This function should be called when an error occurs within the pager
+** code. 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 occured, then the rollback journal may need
+** to be replayed.
+*/
+static void pager_unlock(Pager *pPager);
+static int pager_error(Pager *pPager, int rc){
+int rc2 = rc & 0xff;
+assert(
+pPager->errCode==SQLITE_FULL ||
+pPager->errCode==SQLITE_OK ||
+(pPager->errCode & 0xff)==SQLITE_IOERR
+);
+if(
+rc2==SQLITE_FULL ||
+rc2==SQLITE_IOERR ||
+rc2==SQLITE_CORRUPT
+){
+pPager->errCode = rc;
+if( pPager->state==PAGER_UNLOCK
+&& sqlite3PcacheRefCount(pPager->pPCache)==0
+){
+/* If the pager is already unlocked, call pager_unlock() now to
+** clear the error state and ensure that the pager-cache is
+** completely empty.
+*/
+pager_unlock(pPager);
+}
+}
+return rc;
+}
+/*
+** 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 u32 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 || MEMDB
+|| (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.
+** The master journal file name is read from the end of the file and
+** written into memory supplied by the caller.
+**
+** 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 no master journal file name is present zMaster[0] is set to 0 and
+** SQLITE_OK returned.
+*/
+static int readMasterJournal(sqlite3_file *pJrnl, char *zMaster, int nMaster){
+int rc;
+u32 len;
+i64 szJ;
+u32 cksum;
+u32 u;                   /* Unsigned loop counter */
+unsigned char aMagic[8]; /* A buffer to hold the magic header */
+zMaster[0] = '\0';
+rc = sqlite3OsFileSize(pJrnl, &szJ);
+if( rc!=SQLITE_OK || szJ<16 ) return rc;
+rc = read32bits(pJrnl, szJ-16, &len);
+if( rc!=SQLITE_OK ) return rc;
+if( len>=nMaster ){
+return SQLITE_OK;
+}
+rc = read32bits(pJrnl, szJ-12, &cksum);
+if( rc!=SQLITE_OK ) return rc;
+rc = sqlite3OsRead(pJrnl, aMagic, 8, szJ-8);
+if( rc!=SQLITE_OK || memcmp(aMagic, aJournalMagic, 8) ) return rc;
+rc = sqlite3OsRead(pJrnl, zMaster, len, szJ-16-len);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+zMaster[len] = '\0';
+/* 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.
+*/
+zMaster[0] = '\0';
+}
+return SQLITE_OK;
+}
+/*
+** Seek the journal file descriptor to the next sector boundary where a
+** journal header may be read or written. Pager.journalOff is updated with
+** the new seek offset.
+**
+** i.e for a sector size of 512:
+**
+** Input Offset              Output Offset
+** ---------------------------------------
+** 0                         0
+** 512                       512
+** 100                       512
+** 2000                      2048
+**
+*/
+static void seekJournalHdr(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) );
+pPager->journalOff = offset;
+}
+/*
+** Write zeros over the header of the journal file.  This has the
+** effect of invalidating the journal file and committing the
+** transaction.
+*/
+static int zeroJournalHdr(Pager *pPager, int doTruncate){
+int rc = SQLITE_OK;
+static const char zeroHdr[28] = {0};
+if( pPager->journalOff ){
+i64 iLimit = pPager->journalSizeLimit;
+IOTRACE(("JZEROHDR %p\n", pPager))
+if( doTruncate || iLimit==0 ){
+rc = sqlite3OsTruncate(pPager->jfd, 0);
+}else{
+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;
+char *zHeader = pPager->pTmpSpace;
+int nHeader = pPager->pageSize;
+int nWrite;
+if( nHeader>JOURNAL_HDR_SZ(pPager) ){
+nHeader = JOURNAL_HDR_SZ(pPager);
+}
+if( pPager->stmtHdrOff==0 ){
+pPager->stmtHdrOff = pPager->journalOff;
+}
+seekJournalHdr(pPager);
+pPager->journalHdr = pPager->journalOff;
+memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
+/*
+** 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 occured 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(pPager->fd->pMethods||pPager->noSync);
+if( (pPager->noSync)
+|| (sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND)
+){
+put32bits(&zHeader[sizeof(aJournalMagic)], 0xffffffff);
+}else{
+put32bits(&zHeader[sizeof(aJournalMagic)], 0);
+}
+/* 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->dbSize);
+/* The assumed sector size for this process */
+put32bits(&zHeader[sizeof(aJournalMagic)+12], pPager->sectorSize);
+if( pPager->journalHdr==0 ){
+/* The page size */
+put32bits(&zHeader[sizeof(aJournalMagic)+16], pPager->pageSize);
+}
+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. See comments above function writeJournalHdr() for a description of
+** the journal header format.
+**
+** If the header is read successfully, *nRec is set to the number of
+** page records following this header and *dbSize 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 *nRec and *dbSize are not set.  If JOURNAL_HDR_SZ bytes
+** cannot be read from the journal file an error code is returned.
+*/
+static int readJournalHdr(
+Pager *pPager,
+i64 journalSize,
+u32 *pNRec,
+u32 *pDbSize
+){
+int rc;
+unsigned char aMagic[8]; /* A buffer to hold the magic header */
+i64 jrnlOff;
+int iPageSize;
+seekJournalHdr(pPager);
+if( pPager->journalOff+JOURNAL_HDR_SZ(pPager) > journalSize ){
+return SQLITE_DONE;
+}
+jrnlOff = pPager->journalOff;
+rc = sqlite3OsRead(pPager->jfd, aMagic, sizeof(aMagic), jrnlOff);
+if( rc ) return rc;
+jrnlOff += sizeof(aMagic);
+if( memcmp(aMagic, aJournalMagic, sizeof(aMagic))!=0 ){
+return SQLITE_DONE;
+}
+rc = read32bits(pPager->jfd, jrnlOff, pNRec);
+if( rc ) return rc;
+rc = read32bits(pPager->jfd, jrnlOff+4, &pPager->cksumInit);
+if( rc ) return rc;
+rc = read32bits(pPager->jfd, jrnlOff+8, pDbSize);
+if( rc ) return rc;
+rc = read32bits(pPager->jfd, jrnlOff+16, (u32 *)&iPageSize);
+if( rc==SQLITE_OK
+&& iPageSize>=512
+&& iPageSize<=SQLITE_MAX_PAGE_SIZE
+&& ((iPageSize-1)&iPageSize)==0
+){
+u16 pagesize = iPageSize;
+rc = sqlite3PagerSetPagesize(pPager, &pagesize);
+}
+if( rc ) return rc;
+/* 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.
+*/
+rc = read32bits(pPager->jfd, jrnlOff+12, (u32 *)&pPager->sectorSize);
+if( rc ) return rc;
+pPager->journalOff += JOURNAL_HDR_SZ(pPager);
+return SQLITE_OK;
+}
+/*
+** 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: length of master journal name.
+** + 4 bytes: N
+** + 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.
+**
+** 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;
+int len;
+int i;
+i64 jrnlOff;
+i64 jrnlSize;
+u32 cksum = 0;
+char zBuf[sizeof(aJournalMagic)+2*4];
+if( !zMaster || pPager->setMaster) return SQLITE_OK;
+pPager->setMaster = 1;
+len = strlen(zMaster);
+for(i=0; i<len; i++){
+cksum += zMaster[i];
+}
+/* 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 ){
+seekJournalHdr(pPager);
+}
+jrnlOff = pPager->journalOff;
+pPager->journalOff += (len+20);
+rc = write32bits(pPager->jfd, jrnlOff, PAGER_MJ_PGNO(pPager));
+if( rc!=SQLITE_OK ) return rc;
+jrnlOff += 4;
+rc = sqlite3OsWrite(pPager->jfd, zMaster, len, jrnlOff);
+if( rc!=SQLITE_OK ) return rc;
+jrnlOff += len;
+put32bits(zBuf, len);
+put32bits(&zBuf[4], cksum);
+memcpy(&zBuf[8], aJournalMagic, sizeof(aJournalMagic));
+rc = sqlite3OsWrite(pPager->jfd, zBuf, 8+sizeof(aJournalMagic), jrnlOff);
+jrnlOff += 8+sizeof(aJournalMagic);
+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( (rc==SQLITE_OK)
+&& (rc = sqlite3OsFileSize(pPager->jfd, &jrnlSize))==SQLITE_OK
+&& jrnlSize>jrnlOff
+){
+rc = sqlite3OsTruncate(pPager->jfd, jrnlOff);
+}
+return rc;
+}
+/*
+** Find a page in the hash table given its page number.  Return
+** a pointer to the page or NULL if not found.
+*/
+static PgHdr *pager_lookup(Pager *pPager, Pgno pgno){
+PgHdr *p;
+sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &p);
+return p;
+}
+/*
+** Clear the in-memory cache.  This routine
+** sets the state of the pager back to what it was when it was first
+** opened.  Any outstanding pages are invalidated and subsequent attempts
+** to access those pages will likely result in a coredump.
+*/
+static void pager_reset(Pager *pPager){
+if( pPager->errCode ) return;
+sqlite3PcacheClear(pPager->pPCache);
+}
+/*
+** Unlock the database file.
+**
+** 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 ){
+if( !MEMDB ){
+int rc = osUnlock(pPager->fd, NO_LOCK);
+if( rc ) pPager->errCode = rc;
+pPager->dbSize = -1;
+IOTRACE(("UNLOCK %p\n", pPager))
+/* 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.
+*/
+if( pPager->journalOpen ){
+sqlite3OsClose(pPager->jfd);
+pPager->journalOpen = 0;
+sqlite3BitvecDestroy(pPager->pInJournal);
+pPager->pInJournal = 0;
+sqlite3BitvecDestroy(pPager->pAlwaysRollback);
+pPager->pAlwaysRollback = 0;
+}
+/* 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);
+if( pPager->stmtOpen ){
+sqlite3OsClose(pPager->stfd);
+sqlite3BitvecDestroy(pPager->pInStmt);
+pPager->pInStmt = 0;
+}
+pPager->stmtOpen = 0;
+pPager->stmtInUse = 0;
+pPager->journalOff = 0;
+pPager->journalStarted = 0;
+pPager->stmtAutoopen = 0;
+pPager->origDbSize = 0;
+}
+}
+if( !MEMDB || pPager->errCode==SQLITE_OK ){
+pPager->state = PAGER_UNLOCK;
+pPager->changeCountDone = 0;
+}
+}
+}
+/*
+** 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.
+*/
+static void pagerUnlockAndRollback(Pager *p){
+if( p->errCode==SQLITE_OK && p->state>=PAGER_RESERVED ){
+sqlite3BeginBenignMalloc();
+sqlite3PagerRollback(p);
+sqlite3EndBenignMalloc();
+}
+pager_unlock(p);
+}
+/*
+** This routine ends a transaction.  A transaction is ended by either
+** a COMMIT or a ROLLBACK.
+**
+** When this routine is called, the pager has the journal file open and
+** a RESERVED or EXCLUSIVE lock on the database.  This routine will release
+** the database lock and acquires a SHARED lock in its place if that is
+** the appropriate thing to do.  Release locks usually is appropriate,
+** unless we are in exclusive access mode or unless this is a
+** COMMIT AND BEGIN or ROLLBACK AND BEGIN operation.
+**
+** The journal file is either deleted or truncated.
+**
+** TODO: Consider keeping the journal file open for temporary databases.
+** This might give a performance improvement on windows where opening
+** a file is an expensive operation.
+*/
+static int pager_end_transaction(Pager *pPager, int hasMaster){
+int rc = SQLITE_OK;
+int rc2 = SQLITE_OK;
+assert( !MEMDB );
+if( pPager->state<PAGER_RESERVED ){
+return SQLITE_OK;
+}
+sqlite3PagerStmtCommit(pPager);
+if( pPager->stmtOpen && !pPager->exclusiveMode ){
+sqlite3OsClose(pPager->stfd);
+pPager->stmtOpen = 0;
+}
+if( pPager->journalOpen ){
+if( pPager->journalMode==PAGER_JOURNALMODE_TRUNCATE
+&& (rc = sqlite3OsTruncate(pPager->jfd, 0))==SQLITE_OK ){
+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{
+assert( pPager->journalMode==PAGER_JOURNALMODE_DELETE || rc );
+sqlite3OsClose(pPager->jfd);
+pPager->journalOpen = 0;
+if( rc==SQLITE_OK && !pPager->tempFile ){
+rc = sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
+}
+}
+sqlite3BitvecDestroy(pPager->pInJournal);
+pPager->pInJournal = 0;
+sqlite3BitvecDestroy(pPager->pAlwaysRollback);
+pPager->pAlwaysRollback = 0;
+sqlite3PcacheCleanAll(pPager->pPCache);
+#ifdef SQLITE_CHECK_PAGES
+sqlite3PcacheIterate(pPager->pPCache, pager_set_pagehash);
+#endif
+sqlite3PcacheClearFlags(pPager->pPCache,
+PGHDR_IN_JOURNAL | PGHDR_NEED_SYNC
+);
+pPager->dirtyCache = 0;
+pPager->nRec = 0;
+}else{
+assert( pPager->pInJournal==0 );
+}
+if( !pPager->exclusiveMode ){
+rc2 = osUnlock(pPager->fd, SHARED_LOCK);
+pPager->state = PAGER_SHARED;
+}else if( pPager->state==PAGER_SYNCED ){
+pPager->state = PAGER_EXCLUSIVE;
+}
+pPager->origDbSize = 0;
+pPager->setMaster = 0;
+pPager->needSync = 0;
+/* lruListSetFirstSynced(pPager); */
+pPager->dbSize = -1;
+pPager->dbModified = 0;
+return (rc==SQLITE_OK?rc2:rc);
+}
+/*
+** Compute and return a checksum for the page of data.
+**
+** This is not a real checksum.  It is really just the sum of the
+** random initial value and the page number.  We experimented with
+** a checksum of the entire data, but that was found to be too slow.
+**
+** Note that the page number is stored at the beginning of data and
+** the checksum is stored at the end.  This is important.  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.
+**
+** FIX ME:  Consider adding every 200th (or so) byte of the data to the
+** checksum.  That way if a single page spans 3 or more disk sectors and
+** only the middle sector is corrupt, we will still have a reasonable
+** chance of failing the checksum and thus detecting the problem.
+*/
+static u32 pager_cksum(Pager *pPager, const u8 *aData){
+u32 cksum = pPager->cksumInit;
+int i = pPager->pageSize-200;
+while( i>0 ){
+cksum += aData[i];
+i -= 200;
+}
+return cksum;
+}
+/* Forward declaration */
+static void makeClean(PgHdr*);
+/*
+** Read a single page from the journal file opened on file descriptor
+** jfd.  Playback this one page.
+**
+** 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.
+*/
+static int pager_playback_one_page(
+Pager *pPager,       /* The pager being played back */
+sqlite3_file *jfd,   /* The file that is the journal being rolled back */
+i64 offset,          /* Offset of the page within the journal */
+int isMainJrnl       /* True for main rollback journal. False for Stmt jrnl */
+){
+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 = (u8 *)pPager->pTmpSpace;   /* Temp storage for a page */
+/* isMainJrnl should be true for the main journal and false for
+** statement journals.  Verify that this is always the case
+*/
+assert( jfd == (isMainJrnl ? pPager->jfd : pPager->stfd) );
+assert( aData );
+rc = read32bits(jfd, offset, &pgno);
+if( rc!=SQLITE_OK ) return rc;
+rc = sqlite3OsRead(jfd, aData, pPager->pageSize, offset+4);
+if( rc!=SQLITE_OK ) return rc;
+pPager->journalOff += pPager->pageSize + 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) ){
+return SQLITE_DONE;
+}
+if( pgno>(unsigned)pPager->dbSize ){
+return SQLITE_OK;
+}
+if( isMainJrnl ){
+rc = read32bits(jfd, offset+pPager->pageSize+4, &cksum);
+if( rc ) return rc;
+pPager->journalOff += 4;
+if( pager_cksum(pPager, aData)!=cksum ){
+return SQLITE_DONE;
+}
+}
+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);
+PAGERTRACE4("PLAYBACK %d page %d hash(%08x)\n",
+PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, aData));
+if( (pPager->state>=PAGER_EXCLUSIVE)
+&& (pPg==0 || 0==(pPg->flags&PGHDR_NEED_SYNC))
+&& (pPager->fd->pMethods)
+){
+i64 ofst = (pgno-1)*(i64)pPager->pageSize;
+rc = sqlite3OsWrite(pPager->fd, aData, pPager->pageSize, ofst);
+}
+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);
+if( pPager->xReiniter ){
+pPager->xReiniter(pPg);
+}
+if( isMainJrnl ) makeClean(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);
+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.
+**
+**
+** The master journal file contains the names of all child journals.
+** To tell if a master journal can be deleted, check to each of the
+** children.  If all children are either missing or do not refer to
+** a different master journal, then this master journal can be deleted.
+*/
+static int pager_delmaster(Pager *pPager, const char *zMaster){
+sqlite3_vfs *pVfs = pPager->pVfs;
+int rc;
+int master_open = 0;
+sqlite3_file *pMaster;
+sqlite3_file *pJournal;
+char *zMasterJournal = 0; /* Contents of master journal file */
+i64 nMasterJournal;       /* Size of master journal file */
+/* Open the master journal file exclusively in case some other process
+** is running this routine also. Not that it makes too much difference.
+*/
+pMaster = (sqlite3_file *)sqlite3Malloc(pVfs->szOsFile * 2);
+pJournal = (sqlite3_file *)(((u8 *)pMaster) + pVfs->szOsFile);
+if( !pMaster ){
+rc = SQLITE_NOMEM;
+}else{
+int flags = (SQLITE_OPEN_READONLY|SQLITE_OPEN_MASTER_JOURNAL);
+rc = sqlite3OsOpen(pVfs, zMaster, pMaster, flags, 0);
+}
+if( rc!=SQLITE_OK ) goto delmaster_out;
+master_open = 1;
+rc = sqlite3OsFileSize(pMaster, &nMasterJournal);
+if( rc!=SQLITE_OK ) goto delmaster_out;
+if( nMasterJournal>0 ){
+char *zJournal;
+char *zMasterPtr = 0;
+int nMasterPtr = pPager->pVfs->mxPathname+1;
+/* Load the entire master journal file into space obtained from
+** sqlite3_malloc() and pointed to by zMasterJournal.
+*/
+zMasterJournal = (char *)sqlite3Malloc(nMasterJournal + nMasterPtr);
+if( !zMasterJournal ){
+rc = SQLITE_NOMEM;
+goto delmaster_out;
+}
+zMasterPtr = &zMasterJournal[nMasterJournal];
+rc = sqlite3OsRead(pMaster, zMasterJournal, nMasterJournal, 0);
+if( rc!=SQLITE_OK ) goto delmaster_out;
+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 += (strlen(zJournal)+1);
+}
+}
+rc = sqlite3OsDelete(pVfs, zMaster, 0);
+delmaster_out:
+if( zMasterJournal ){
+sqlite3_free(zMasterJournal);
+}
+if( master_open ){
+sqlite3OsClose(pMaster);
+}
+sqlite3_free(pMaster);
+return rc;
+}
+static void pager_truncate_cache(Pager *pPager);
+/*
+** Truncate the main file of the given pager to the number of pages
+** indicated. Also truncate the cached representation of the file.
+**
+** Might might be the case that the file on disk is smaller than nPage.
+** This can happen, for example, if we are in the middle of a transaction
+** which has extended the file size and the new pages are still all held
+** in cache, then an INSERT or UPDATE does a statement rollback.  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.
+*/
+static int pager_truncate(Pager *pPager, int nPage){
+int rc = SQLITE_OK;
+if( pPager->state>=PAGER_EXCLUSIVE && pPager->fd->pMethods ){
+i64 currentSize, newSize;
+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->dbSize = nPage;
+pager_truncate_cache(pPager);
+}
+return rc;
+}
+/*
+** Set the sectorSize for the given pager.
+**
+** The sector size is at least as big as the sector size reported
+** by sqlite3OsSectorSize().  The minimum sector size is 512.
+*/
+static void setSectorSize(Pager *pPager){
+assert(pPager->fd->pMethods||pPager->tempFile);
+if( !pPager->tempFile ){
+/* Sector size doesn't matter for temporary files. Also, the file
+** may not have been opened yet, in whcih case the OsSectorSize()
+** call will segfault.
+*/
+pPager->sectorSize = sqlite3OsSectorSize(pPager->fd);
+}
+if( pPager->sectorSize<512 ){
+pPager->sectorSize = 512;
+}
+}
+/*
+** 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.
+*/
+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 */
+/* Figure out how many records are in the journal.  Abort early if
+** the journal is empty.
+*/
+assert( pPager->journalOpen );
+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.
+*/
+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;
+/* This loop terminates either when the readJournalHdr() call returns
+** SQLITE_DONE or an IO error occurs. */
+while( 1 ){
+/* 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, 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 = (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.
+*/
+if( nRec==0 && !isHot &&
+pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff ){
+nRec = (szJ - pPager->journalOff) / JOURNAL_PG_SZ(pPager);
+}
+/* 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;
+}
+}
+/* Copy original pages out of the journal and back into the database file.
+*/
+for(u=0; u<nRec; u++){
+rc = pager_playback_one_page(pPager, pPager->jfd, pPager->journalOff, 1);
+if( rc!=SQLITE_OK ){
+if( rc==SQLITE_DONE ){
+rc = SQLITE_OK;
+pPager->journalOff = szJ;
+break;
+}else{
+/* If we are unable to rollback, then the database is probably
+** going to end up being corrupt.  It is corrupt to us, anyhow.
+** Perhaps the next process to come along can fix it....
+*/
+rc = SQLITE_CORRUPT_BKPT;
+goto end_playback;
+}
+}
+}
+}
+/*NOTREACHED*/
+assert( 0 );
+end_playback:
+if( rc==SQLITE_OK ){
+zMaster = pPager->pTmpSpace;
+rc = readMasterJournal(pPager->jfd, zMaster, pPager->pVfs->mxPathname+1);
+}
+if( rc==SQLITE_OK ){
+rc = pager_end_transaction(pPager, zMaster[0]!='\0');
+}
+if( rc==SQLITE_OK && zMaster[0] ){
+/* 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);
+}
+/* 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 the statement journal.
+**
+** This is similar to playing back the transaction journal but with
+** a few extra twists.
+**
+**    (1)  The number of pages in the database file at the start of
+**         the statement is stored in pPager->stmtSize, not in the
+**         journal file itself.
+**
+**    (2)  In addition to playing back the statement journal, also
+**         playback all pages of the transaction journal beginning
+**         at offset pPager->stmtJSize.
+*/
+static int pager_stmt_playback(Pager *pPager){
+i64 szJ;                 /* Size of the full journal */
+i64 hdrOff;
+int nRec;                /* Number of Records */
+int i;                   /* Loop counter */
+int rc;
+szJ = pPager->journalOff;
+/* Set hdrOff to be the offset just after the end of the last journal
+** page written before the first journal-header for this statement
+** transaction was written, or the end of the file if no journal
+** header was written.
+*/
+hdrOff = pPager->stmtHdrOff;
+assert( pPager->fullSync || !hdrOff );
+if( !hdrOff ){
+hdrOff = szJ;
+}
+/* Truncate the database back to its original size.
+*/
+rc = pager_truncate(pPager, pPager->stmtSize);
+assert( pPager->state>=PAGER_SHARED );
+/* Figure out how many records are in the statement journal.
+*/
+assert( pPager->stmtInUse && pPager->journalOpen );
+nRec = pPager->stmtNRec;
+/* Copy original pages out of the statement journal and back into the
+** database file.  Note that the statement journal omits checksums from
+** each record since power-failure recovery is not important to statement
+** journals.
+*/
+for(i=0; i<nRec; i++){
+i64 offset = i*(4+pPager->pageSize);
+rc = pager_playback_one_page(pPager, pPager->stfd, offset, 0);
+assert( rc!=SQLITE_DONE );
+if( rc!=SQLITE_OK ) goto end_stmt_playback;
+}
+/* Now roll some pages back from the transaction journal. Pager.stmtJSize
+** was the size of the journal file when this statement was started, so
+** everything after that needs to be rolled back, either into the
+** database, the memory cache, or both.
+**
+** If it is not zero, then Pager.stmtHdrOff is the offset to the start
+** of the first journal header written during this statement transaction.
+*/
+pPager->journalOff = pPager->stmtJSize;
+pPager->cksumInit = pPager->stmtCksum;
+while( pPager->journalOff < hdrOff ){
+rc = pager_playback_one_page(pPager, pPager->jfd, pPager->journalOff, 1);
+assert( rc!=SQLITE_DONE );
+if( rc!=SQLITE_OK ) goto end_stmt_playback;
+}
+while( pPager->journalOff < szJ ){
+u32 nJRec;         /* Number of Journal Records */
+u32 dummy;
+rc = readJournalHdr(pPager, szJ, &nJRec, &dummy);
+if( rc!=SQLITE_OK ){
+assert( rc!=SQLITE_DONE );
+goto end_stmt_playback;
+}
+if( nJRec==0 ){
+nJRec = (szJ - pPager->journalOff) / (pPager->pageSize+8);
+}
+for(i=nJRec-1; i>=0 && pPager->journalOff < szJ; i--){
+rc = pager_playback_one_page(pPager, pPager->jfd, pPager->journalOff, 1);
+assert( rc!=SQLITE_DONE );
+if( rc!=SQLITE_OK ) goto end_stmt_playback;
+}
+}
+pPager->journalOff = szJ;
+end_stmt_playback:
+if( rc==SQLITE_OK) {
+pPager->journalOff = szJ;
+/* pager_reload_cache(pPager); */
+}
+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 || MEMDB;
+pPager->fullSync = level==3 && !pPager->tempFile;
+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 *fd.  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.
+*/
+static int sqlite3PagerOpentemp(
+Pager *pPager,        /* The pager object */
+sqlite3_file *pFile,  /* Write the file descriptor here */
+int vfsFlags          /* Flags passed through to the VFS */
+){
+int rc;
+#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 || pFile->pMethods );
+return rc;
+}
+static int pagerStress(void *,PgHdr *);
+/*
+** Create a new page cache and put a pointer to the page cache in *ppPager.
+** The file to be cached need not exist.  The file is not locked until
+** the first call to sqlite3PagerGet() and is only held open until the
+** last page is released using sqlite3PagerUnref().
+**
+** If zFilename is NULL then a randomly-named temporary file is created
+** and used as the file to be cached.  The file will be deleted
+** automatically when it is 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.
+*/
+int sqlite3PagerOpen(
+sqlite3_vfs *pVfs,       /* The virtual file system to use */
+Pager **ppPager,         /* 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() */
+){
+u8 *pPtr;
+Pager *pPager = 0;
+int rc = SQLITE_OK;
+int i;
+int tempFile = 0;
+int memDb = 0;
+int readOnly = 0;
+int useJournal = (flags & PAGER_OMIT_JOURNAL)==0;
+int noReadlock = (flags & PAGER_NO_READLOCK)!=0;
+int journalFileSize = sqlite3JournalSize(pVfs);
+int pcacheSize = sqlite3PcacheSize();
+int szPageDflt = SQLITE_DEFAULT_PAGE_SIZE;
+char *zPathname = 0;
+int nPathname = 0;
+/* The default return is a NULL pointer */
+*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;
+useJournal = 0;
+}else
+#endif
+{
+rc = sqlite3OsFullPathname(pVfs, zFilename, nPathname, zPathname);
+}
+if( rc!=SQLITE_OK ){
+sqlite3_free(zPathname);
+return rc;
+}
+nPathname = strlen(zPathname);
+}
+/* Allocate memory for the pager structure */
+pPager = sqlite3MallocZero(
+sizeof(*pPager) +           /* Pager structure */
+pcacheSize      +           /* PCache object */
+journalFileSize +           /* The journal file structure */
+pVfs->szOsFile * 3 +        /* The main db and two journal files */
+3*nPathname + 40            /* zFilename, zDirectory, zJournal */
+);
+if( !pPager ){
+sqlite3_free(zPathname);
+return SQLITE_NOMEM;
+}
+pPager->pPCache = (PCache *)&pPager[1];
+pPtr = ((u8 *)&pPager[1]) + pcacheSize;
+pPager->vfsFlags = vfsFlags;
+pPager->fd = (sqlite3_file*)&pPtr[pVfs->szOsFile*0];
+pPager->stfd = (sqlite3_file*)&pPtr[pVfs->szOsFile*1];
+pPager->jfd = (sqlite3_file*)&pPtr[pVfs->szOsFile*2];
+pPager->zFilename = (char*)&pPtr[pVfs->szOsFile*2+journalFileSize];
+pPager->zDirectory = &pPager->zFilename[nPathname+1];
+pPager->zJournal = &pPager->zDirectory[nPathname+1];
+pPager->pVfs = pVfs;
+if( zPathname ){
+memcpy(pPager->zFilename, zPathname, nPathname+1);
+sqlite3_free(zPathname);
+}
+/* Open the pager file.
+*/
+if( zFilename && zFilename[0] && !memDb ){
+if( nPathname>(pVfs->mxPathname - sizeof("-journal")) ){
+rc = SQLITE_CANTOPEN;
+}else{
+int fout = 0;
+rc = sqlite3OsOpen(pVfs, pPager->zFilename, pPager->fd,
+pPager->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 ){
+int iSectorSize = sqlite3OsSectorSize(pPager->fd);
+if( szPageDflt<iSectorSize ){
+szPageDflt = iSectorSize;
+}
+#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
+if( szPageDflt>SQLITE_MAX_DEFAULT_PAGE_SIZE ){
+szPageDflt = SQLITE_MAX_DEFAULT_PAGE_SIZE;
+}
+}
+}
+}else if( !memDb ){
+/* 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().
+*/
+tempFile = 1;
+pPager->state = PAGER_EXCLUSIVE;
+}
+if( pPager && rc==SQLITE_OK ){
+pPager->pTmpSpace = sqlite3PageMalloc(szPageDflt);
+}
+/* If an error occured in either of the blocks above.
+** Free the Pager structure and close the file.
+** Since the pager is not allocated there is no need to set
+** any Pager.errMask variables.
+*/
+if( !pPager || !pPager->pTmpSpace ){
+sqlite3OsClose(pPager->fd);
+sqlite3_free(pPager);
+return ((rc==SQLITE_OK)?SQLITE_NOMEM:rc);
+}
+nExtra = FORCE_ALIGNMENT(nExtra);
+sqlite3PcacheOpen(szPageDflt, nExtra, !memDb,
+!memDb?pagerStress:0, (void *)pPager, pPager->pPCache);
+PAGERTRACE3("OPEN %d %s\n", FILEHANDLEID(pPager->fd), pPager->zFilename);
+IOTRACE(("OPEN %p %s\n", pPager, pPager->zFilename))
+/* Fill in Pager.zDirectory[] */
+memcpy(pPager->zDirectory, pPager->zFilename, nPathname+1);
+for(i=strlen(pPager->zDirectory); i>0 && pPager->zDirectory[i-1]!='/'; i--){}
+if( i>0 ) pPager->zDirectory[i-1] = 0;
+/* Fill in Pager.zJournal[] */
+if( zPathname ){
+memcpy(pPager->zJournal, pPager->zFilename, nPathname);
+memcpy(&pPager->zJournal[nPathname], "-journal", 9);
+}else{
+pPager->zJournal = 0;
+}
+/* pPager->journalOpen = 0; */
+pPager->useJournal = useJournal;
+pPager->noReadlock = noReadlock && readOnly;
+/* pPager->stmtOpen = 0; */
+/* pPager->stmtInUse = 0; */
+/* pPager->nRef = 0; */
+pPager->dbSize = memDb-1;
+pPager->pageSize = szPageDflt;
+/* pPager->stmtSize = 0; */
+/* pPager->stmtJSize = 0; */
+/* pPager->nPage = 0; */
+pPager->mxPage = 100;
+pPager->mxPgno = SQLITE_MAX_PAGE_COUNT;
+/* pPager->state = PAGER_UNLOCK; */
+assert( pPager->state == (tempFile ? PAGER_EXCLUSIVE : PAGER_UNLOCK) );
+/* pPager->errMask = 0; */
+pPager->tempFile = tempFile;
+assert( tempFile==PAGER_LOCKINGMODE_NORMAL
+|| tempFile==PAGER_LOCKINGMODE_EXCLUSIVE );
+assert( PAGER_LOCKINGMODE_EXCLUSIVE==1 );
+pPager->exclusiveMode = tempFile;
+pPager->memDb = memDb;
+pPager->readOnly = readOnly;
+/* pPager->needSync = 0; */
+pPager->noSync = pPager->tempFile || !useJournal;
+pPager->fullSync = (pPager->noSync?0:1);
+pPager->sync_flags = SQLITE_SYNC_NORMAL;
+/* pPager->pFirst = 0; */
+/* pPager->pFirstSynced = 0; */
+/* pPager->pLast = 0; */
+pPager->nExtra = nExtra;
+pPager->journalSizeLimit = SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT;
+assert(pPager->fd->pMethods||memDb||tempFile);
+if( !memDb ){
+setSectorSize(pPager);
+}
+/* pPager->pBusyHandler = 0; */
+/* memset(pPager->aHash, 0, sizeof(pPager->aHash)); */
+*ppPager = pPager;
+return SQLITE_OK;
+}
+/*
+** Set the busy handler function.
+*/
+void sqlite3PagerSetBusyhandler(Pager *pPager, BusyHandler *pBusyHandler){
+pPager->pBusyHandler = pBusyHandler;
+}
+/*
+** Set the reinitializer for this pager.  If not NULL, the reinitializer
+** is called when the content of a page in cache is restored to its original
+** value as a result of a rollback.  The callback gives higher-level code
+** an opportunity to restore the EXTRA section to agree with the restored
+** page data.
+*/
+void sqlite3PagerSetReiniter(Pager *pPager, void (*xReinit)(DbPage*)){
+pPager->xReiniter = xReinit;
+}
+/*
+** Set the page size to *pPageSize. If the suggest new page size is
+** inappropriate, then an alternative page size is set to that
+** value before returning.
+*/
+int sqlite3PagerSetPagesize(Pager *pPager, u16 *pPageSize){
+int rc = pPager->errCode;
+if( rc==SQLITE_OK ){
+u16 pageSize = *pPageSize;
+assert( pageSize==0 || (pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE) );
+if( pageSize && pageSize!=pPager->pageSize
+&& (pPager->memDb==0 || pPager->dbSize==0)
+&& sqlite3PcacheRefCount(pPager->pPCache)==0
+){
+char *pNew = (char *)sqlite3PageMalloc(pageSize);
+if( !pNew ){
+rc = SQLITE_NOMEM;
+}else{
+pager_reset(pPager);
+pPager->pageSize = pageSize;
+if( !pPager->memDb ) setSectorSize(pPager);
+sqlite3PageFree(pPager->pTmpSpace);
+pPager->pTmpSpace = pNew;
+sqlite3PcacheSetPageSize(pPager->pPCache, pageSize);
+}
+}
+*pPageSize = pPager->pageSize;
+}
+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.
+**
+** No error checking is done. The rational for this is that this function
+** may be called even if the file does not exist or contain a header. In
+** these cases sqlite3OsRead() will return an error, to which the correct
+** response is to zero the memory at pDest and continue.  A real IO error
+** will presumably recur and be picked up later (Todo: Think about this).
+*/
+int sqlite3PagerReadFileheader(Pager *pPager, int N, unsigned char *pDest){
+int rc = SQLITE_OK;
+memset(pDest, 0, N);
+assert(MEMDB||pPager->fd->pMethods||pPager->tempFile);
+if( pPager->fd->pMethods ){
+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 disk file associated with
+** pPager.
+**
+** If the PENDING_BYTE lies on the page directly after the end of the
+** file, then consider this page part of the file too. For example, if
+** PENDING_BYTE is byte 4096 (the first byte of page 5) and the size of the
+** file is 4096 bytes, 5 is returned instead of 4.
+*/
+int sqlite3PagerPagecount(Pager *pPager, int *pnPage){
+i64 n = 0;
+int rc;
+assert( pPager!=0 );
+if( pPager->errCode ){
+rc = pPager->errCode;
+return rc;
+}
+if( pPager->dbSize>=0 ){
+n = pPager->dbSize;
+} else {
+assert(pPager->fd->pMethods||pPager->tempFile);
+if( (pPager->fd->pMethods)
+&& (rc = sqlite3OsFileSize(pPager->fd, &n))!=SQLITE_OK ){
+pager_error(pPager, rc);
+return rc;
+}
+if( n>0 && n<pPager->pageSize ){
+n = 1;
+}else{
+n /= pPager->pageSize;
+}
+if( pPager->state!=PAGER_UNLOCK ){
+pPager->dbSize = n;
+}
+}
+if( n==(PENDING_BYTE/pPager->pageSize) ){
+n++;
+}
+if( n>pPager->mxPgno ){
+pPager->mxPgno = n;
+}
+if( pnPage ){
+*pnPage = n;
+}
+return SQLITE_OK;
+}
+/*
+** Forward declaration
+*/
+static int syncJournal(Pager*);
+/*
+** This routine is used to truncate the cache when a database
+** is truncated.  Drop from the cache all pages whose pgno is
+** larger than pPager->dbSize and is unreferenced.
+**
+** Referenced pages larger than pPager->dbSize are zeroed.
+**
+** Actually, at the point this routine is called, it would be
+** an error to have a referenced page.  But rather than delete
+** that page and guarantee a subsequent segfault, it seems better
+** to zero it and hope that we error out sanely.
+*/
+static void pager_truncate_cache(Pager *pPager){
+sqlite3PcacheTruncate(pPager->pPCache, pPager->dbSize);
+}
+/*
+** Try to obtain a lock on a file.  Invoke the busy callback if the lock
+** is currently not available.  Repeat until the busy callback returns
+** false or until the lock succeeds.
+**
+** Return SQLITE_OK on success and an error code if we cannot obtain
+** the lock.
+*/
+static int pager_wait_on_lock(Pager *pPager, int locktype){
+int rc;
+/* 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->dbSize<0 || MEMDB );
+if( pPager->state>=locktype ){
+rc = SQLITE_OK;
+}else{
+if( pPager->pBusyHandler ) pPager->pBusyHandler->nBusy = 0;
+do {
+rc = sqlite3OsLock(pPager->fd, locktype);
+}while( rc==SQLITE_BUSY && sqlite3InvokeBusyHandler(pPager->pBusyHandler) );
+if( rc==SQLITE_OK ){
+pPager->state = locktype;
+IOTRACE(("LOCK %p %d\n", pPager, locktype))
+}
+}
+return rc;
+}
+/*
+** Truncate the file to the number of pages specified.
+*/
+int sqlite3PagerTruncate(Pager *pPager, Pgno nPage){
+int rc = SQLITE_OK;
+assert( pPager->state>=PAGER_SHARED || MEMDB );
+sqlite3PagerPagecount(pPager, 0);
+if( pPager->errCode ){
+rc = pPager->errCode;
+}else if( nPage<(unsigned)pPager->dbSize ){
+if( MEMDB ){
+pPager->dbSize = nPage;
+pager_truncate_cache(pPager);
+}else{
+rc = syncJournal(pPager);
+if( rc==SQLITE_OK ){
+/* Get an exclusive lock on the database before truncating. */
+rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
+}
+if( rc==SQLITE_OK ){
+rc = pager_truncate(pPager, nPage);
+}
+}
+}
+return rc;
+}
+/*
+** 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);
+pagerUnlockAndRollback(pPager);
+enable_simulated_io_errors();
+sqlite3EndBenignMalloc();
+PAGERTRACE2("CLOSE %d\n", PAGERID(pPager));
+IOTRACE(("CLOSE %p\n", pPager))
+if( pPager->journalOpen ){
+sqlite3OsClose(pPager->jfd);
+}
+sqlite3BitvecDestroy(pPager->pInJournal);
+sqlite3BitvecDestroy(pPager->pAlwaysRollback);
+if( pPager->stmtOpen ){
+sqlite3OsClose(pPager->stfd);
+}
+sqlite3OsClose(pPager->fd);
+/* Temp files are automatically deleted by the OS
+** if( pPager->tempFile ){
+**   sqlite3OsDelete(pPager->zFilename);
+** }
+*/
+sqlite3PageFree(pPager->pTmpSpace);
+sqlite3PcacheClose(pPager->pPCache);
+sqlite3_free(pPager);
+return SQLITE_OK;
+}
+#if !defined(NDEBUG) || defined(SQLITE_TEST)
+/*
+** Return the page number for the given page data.
+*/
+Pgno sqlite3PagerPagenumber(DbPage *p){
+return p->pgno;
+}
+#endif
+/*
+** Increment the reference count for a page.  The input pointer is
+** a reference to the page data.
+*/
+int sqlite3PagerRef(DbPage *pPg){
+sqlite3PcacheRef(pPg);
+return SQLITE_OK;
+}
+/*
+** 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.  It is not safe to modify the original database file until after
+** the journal has been synced.  If the original database is modified before
+** the journal is synced and a power failure occurs, the unsynced journal
+** data would be lost and we would be unable to completely rollback the
+** database changes.  Database corruption would occur.
+**
+** This routine also updates the nRec field in the header of the journal.
+** (See comments on the pager_playback() routine for additional information.)
+** If the sync mode is FULL, two syncs will occur.  First the whole journal
+** is synced, then the nRec field is updated, then a second sync occurs.
+**
+** For temporary databases, we do not care if we are able to rollback
+** after a power failure, so no sync occurs.
+**
+** If the IOCAP_SEQUENTIAL flag is set for the persistent media on which
+** the database is stored, then OsSync() is never called on the journal
+** file. In this case all that is required is to update the nRec field in
+** the journal header.
+**
+** This routine clears the needSync field of every page current held in
+** memory.
+*/
+static int syncJournal(Pager *pPager){
+int rc = SQLITE_OK;
+/* Sync the journal before modifying the main database
+** (assuming there is a journal and it needs to be synced.)
+*/
+if( pPager->needSync ){
+if( !pPager->tempFile ){
+int iDc = sqlite3OsDeviceCharacteristics(pPager->fd);
+assert( pPager->journalOpen );
+if( 0==(iDc&SQLITE_IOCAP_SAFE_APPEND) ){
+/* 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.
+*/
+i64 jrnlOff;
+if( pPager->fullSync && 0==(iDc&SQLITE_IOCAP_SEQUENTIAL) ){
+PAGERTRACE2("SYNC journal of %d\n", PAGERID(pPager));
+IOTRACE(("JSYNC %p\n", pPager))
+rc = sqlite3OsSync(pPager->jfd, pPager->sync_flags);
+if( rc!=0 ) return rc;
+}
+jrnlOff = pPager->journalHdr + sizeof(aJournalMagic);
+IOTRACE(("JHDR %p %lld %d\n", pPager, jrnlOff, 4));
+rc = write32bits(pPager->jfd, jrnlOff, pPager->nRec);
+if( rc ) return rc;
+}
+if( 0==(iDc&SQLITE_IOCAP_SEQUENTIAL) ){
+PAGERTRACE2("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!=0 ) return rc;
+}
+pPager->journalStarted = 1;
+}
+pPager->needSync = 0;
+/* Erase the needSync flag from every page.
+*/
+sqlite3PcacheClearFlags(pPager->pPCache, PGHDR_NEED_SYNC);
+}
+#ifndef NDEBUG
+/* If the Pager.needSync flag is clear then the PgHdr.needSync
+** flag must also be clear for all pages.  Verify that this
+** invariant is true.
+*/
+else{
+sqlite3PcacheAssertFlags(pPager->pPCache, 0, PGHDR_NEED_SYNC);
+}
+#endif
+return rc;
+}
+/*
+** Given a list of pages (connected by the PgHdr.pDirty pointer) write
+** every one of those pages out to the database file. No calls are made
+** to the page-cache to mark the pages as clean. It is the responsibility
+** of the caller to use PcacheCleanAll() or PcacheMakeClean() to mark
+** the pages as clean.
+*/
+static int pager_write_pagelist(PgHdr *pList){
+Pager *pPager;
+int rc;
+if( 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
+** calls to sqlite3OsLock() are no-ops.
+**
+** 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.
+*/
+rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+while( pList ){
+/* If the file has not yet been opened, open it now. */
+if( !pPager->fd->pMethods ){
+assert(pPager->tempFile);
+rc = sqlite3PagerOpentemp(pPager, pPager->fd, pPager->vfsFlags);
+if( rc ) return rc;
+}
+/* If there are dirty pages in the page cache with page numbers greater
+** than Pager.dbSize, this means sqlite3PagerTruncate() was called to
+** make the file smaller (presumably by auto-vacuum code). Do not write
+** any such pages to the file.
+*/
+if( pList->pgno<=pPager->dbSize && 0==(pList->flags&PGHDR_DONT_WRITE) ){
+i64 offset = (pList->pgno-1)*(i64)pPager->pageSize;
+char *pData = CODEC2(pPager, pList->pData, pList->pgno, 6);
+PAGERTRACE4("STORE %d page %d hash(%08x)\n",
+PAGERID(pPager), pList->pgno, pager_pagehash(pList));
+IOTRACE(("PGOUT %p %d\n", pPager, pList->pgno));
+rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize, offset);
+PAGER_INCR(sqlite3_pager_writedb_count);
+PAGER_INCR(pPager->nWrite);
+if( pList->pgno==1 ){
+memcpy(&pPager->dbFileVers, &pData[24], sizeof(pPager->dbFileVers));
+}
+}
+#ifndef NDEBUG
+else{
+PAGERTRACE3("NOSTORE %d page %d\n", PAGERID(pPager), pList->pgno);
+}
+#endif
+if( rc ) return rc;
+#ifdef SQLITE_CHECK_PAGES
+pList->pageHash = pager_pagehash(pList);
+#endif
+pList = pList->pDirty;
+}
+return SQLITE_OK;
+}
+/*
+** This function is called by the pcache layer when it has reached some
+** soft memory limit. The argument is a pointer to a purgeable Pager
+** object. This function attempts to make a single dirty page that has no
+** outstanding references (if one exists) clean so that it can be recycled
+** by the pcache layer.
+*/
+static int pagerStress(void *p, PgHdr *pPg){
+Pager *pPager = (Pager *)p;
+int rc = SQLITE_OK;
+if( pPager->doNotSync ){
+return SQLITE_OK;
+}
+assert( pPg->flags&PGHDR_DIRTY );
+if( pPager->errCode==SQLITE_OK ){
+if( pPg->flags&PGHDR_NEED_SYNC ){
+rc = syncJournal(pPager);
+if( rc==SQLITE_OK && pPager->fullSync &&
+!(sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND)
+){
+pPager->nRec = 0;
+rc = writeJournalHdr(pPager);
+}
+}
+if( rc==SQLITE_OK ){
+pPg->pDirty = 0;
+rc = pager_write_pagelist(pPg);
+}
+if( rc!=SQLITE_OK ){
+pager_error(pPager, rc);
+}
+}
+if( rc==SQLITE_OK ){
+sqlite3PcacheMakeClean(pPg);
+}
+return rc;
+}
+/*
+** Return 1 if there is a hot journal on the given pager.
+** A hot journal is one that needs to be played back.
+**
+** 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.  Just delete the journal.
+**
+** Return negative if unable to determine the status of the journal.
+**
+** This routine does not open the journal file to examine its
+** content.  Hence, the journal might contain the name of a master
+** journal file that has been deleted, and hence not be hot.  Or
+** the header of the journal might be zeroed out.  This routine
+** does not discover these cases of a non-hot journal - if the
+** journal file exists and is not empty this routine assumes it
+** is hot.  The pager_playback() routine will discover that the
+** journal file is not really hot and will no-op.
+*/
+static int hasHotJournal(Pager *pPager, int *pExists){
+sqlite3_vfs *pVfs = pPager->pVfs;
+int rc = SQLITE_OK;
+int exists;
+int locked;
+assert( pPager!=0 );
+assert( pPager->useJournal );
+assert( pPager->fd->pMethods );
+*pExists = 0;
+rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists);
+if( rc==SQLITE_OK && exists ){
+rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
+}
+if( rc==SQLITE_OK && exists && !locked ){
+int nPage;
+rc = sqlite3PagerPagecount(pPager, &nPage);
+if( rc==SQLITE_OK ){
+if( nPage==0 ){
+sqlite3OsDelete(pVfs, pPager->zJournal, 0);
+}else{
+*pExists = 1;
+}
+}
+}
+return rc;
+}
+/*
+** Read the content of page pPg out of the database file.
+*/
+static int readDbPage(Pager *pPager, PgHdr *pPg, Pgno pgno){
+int rc;
+i64 offset;
+assert( MEMDB==0 );
+assert(pPager->fd->pMethods||pPager->tempFile);
+if( !pPager->fd->pMethods ){
+return SQLITE_IOERR_SHORT_READ;
+}
+offset = (pgno-1)*(i64)pPager->pageSize;
+rc = sqlite3OsRead(pPager->fd, pPg->pData, pPager->pageSize, offset);
+PAGER_INCR(sqlite3_pager_readdb_count);
+PAGER_INCR(pPager->nRead);
+IOTRACE(("PGIN %p %d\n", pPager, pgno));
+if( pgno==1 ){
+memcpy(&pPager->dbFileVers, &((u8*)pPg->pData)[24],
+sizeof(pPager->dbFileVers));
+}
+CODEC1(pPager, pPg->pData, pPg->pgno, 3);
+PAGERTRACE4("FETCH %d page %d hash(%08x)\n",
+PAGERID(pPager), pPg->pgno, pager_pagehash(pPg));
+return rc;
+}
+/*
+** This function is called to obtain the shared lock required before
+** data may be read from the pager cache. If the shared lock has already
+** been obtained, this function is a no-op.
+**
+** Immediately after obtaining the shared lock (if required), this function
+** checks for a hot-journal file. If one is found, an emergency rollback
+** is performed immediately.
+*/
+static int pagerSharedLock(Pager *pPager){
+int rc = SQLITE_OK;
+int isErrorReset = 0;
+/* If this database is opened for exclusive access, has no outstanding
+** page references and is in an error-state, now is the chance to clear
+** the error. Discard the contents of the pager-cache and treat any
+** open journal file as a hot-journal.
+*/
+if( !MEMDB && pPager->exclusiveMode
+&& sqlite3PcacheRefCount(pPager->pPCache)==0 && pPager->errCode
+){
+if( pPager->journalOpen ){
+isErrorReset = 1;
+}
+pPager->errCode = SQLITE_OK;
+pager_reset(pPager);
+}
+/* If the pager is still in an error state, do not proceed. The error
+** state will be cleared at some point in the future when all page
+** references are dropped and the cache can be discarded.
+*/
+if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
+return pPager->errCode;
+}
+if( pPager->state==PAGER_UNLOCK || isErrorReset ){
+sqlite3_vfs *pVfs = pPager->pVfs;
+if( !MEMDB ){
+int isHotJournal;
+assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
+if( !pPager->noReadlock ){
+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 ){
+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 it
+** back.
+**
+** Because the intermediate RESERVED lock is not requested, the
+** second process 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( !isErrorReset && pPager->journalOpen==0 ){
+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 || pPager->jfd->pMethods );
+if( fout&SQLITE_OPEN_READONLY ){
+rc = SQLITE_BUSY;
+sqlite3OsClose(pPager->jfd);
+}
+}else{
+/* If the journal does not exist, that means some other process
+** has already rolled it back */
+rc = SQLITE_BUSY;
+}
+}
+}
+if( rc!=SQLITE_OK ){
+if( rc!=SQLITE_NOMEM && rc!=SQLITE_IOERR_UNLOCK
+&& rc!=SQLITE_IOERR_NOMEM
+){
+rc = SQLITE_BUSY;
+}
+goto failed;
+}
+pPager->journalOpen = 1;
+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.
+*/
+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( 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;
+}
+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 );
+if( pPager->state==PAGER_UNLOCK ){
+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;
+}
+/*
+** Make sure we have the content for a page.  If the page was
+** previously acquired with noContent==1, then the content was
+** just initialized to zeros instead of being read from disk.
+** But now we need the real data off of disk.  So make sure we
+** have it.  Read it in if we do not have it already.
+*/
+static int pager_get_content(PgHdr *pPg){
+if( pPg->flags&PGHDR_NEED_READ ){
+int rc = readDbPage(pPg->pPager, pPg, pPg->pgno);
+if( rc==SQLITE_OK ){
+pPg->flags &= ~PGHDR_NEED_READ;
+}else{
+return rc;
+}
+}
+return SQLITE_OK;
+}
+/*
+** If the reference count has reached zero, and the pager is not in the
+** middle of a write transaction or opened in exclusive mode, unlock it.
+*/
+static void pagerUnlockIfUnused(Pager *pPager){
+if( (sqlite3PcacheRefCount(pPager->pPCache)==0)
+&& (!pPager->exclusiveMode || pPager->journalOff>0)
+){
+pagerUnlockAndRollback(pPager);
+}
+}
+/*
+** Drop a page from the cache using sqlite3PcacheDrop().
+**
+** If this means there are now no pages with references to them, a rollback
+** occurs and the lock on the database is removed.
+*/
+static void pagerDropPage(DbPage *pPg){
+Pager *pPager = pPg->pPager;
+sqlite3PcacheDrop(pPg);
+pagerUnlockIfUnused(pPager);
+}
+/*
+** Acquire a page.
+**
+** A read lock on the disk file is obtained when the first page is acquired.
+** This read lock is dropped when the last page is released.
+**
+** This routine works for any page number greater than 0.  If the database
+** file is smaller than the requested page, then no actual disk
+** read occurs and the memory image of the page is initialized to
+** all zeros.  The extra data appended to a page is always initialized
+** to zeros the first time a page is loaded into memory.
+**
+** 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.
+**
+** If noContent is false, the page contents are actually read from disk.
+** If noContent is true, it means that we do not care about the contents
+** of the page at this time, so do not do a disk read.  Just fill in the
+** page content with zeros.  But mark the fact that we have not read the
+** content by setting the PgHdr.needRead flag.  Later on, if
+** sqlite3PagerWrite() is called on this page or if this routine is
+** called again with noContent==0, that means that the content is needed
+** and the disk read should occur at that point.
+*/
+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 */
+){
+PgHdr *pPg = 0;
+int rc;
+assert( pPager->state==PAGER_UNLOCK
+|| sqlite3PcacheRefCount(pPager->pPCache)>0
+|| pgno==1
+);
+/* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
+** number greater than this, or zero, is requested.
+*/
+if( pgno>PAGER_MAX_PGNO || pgno==0 || pgno==PAGER_MJ_PGNO(pPager) ){
+return SQLITE_CORRUPT_BKPT;
+}
+/* Make sure we have not hit any critical errors.
+*/
+assert( pPager!=0 );
+*ppPage = 0;
+/* If this is the first page accessed, then get a SHARED lock
+** on the database file. pagerSharedLock() is a no-op if
+** a database lock is already held.
+*/
+rc = pagerSharedLock(pPager);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+assert( pPager->state!=PAGER_UNLOCK );
+rc = sqlite3PcacheFetch(pPager->pPCache, pgno, 1, &pPg);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+if( pPg->pPager==0 ){
+/* The pager cache has created a new page. Its content needs to
+** be initialized.
+*/
+int nMax;
+PAGER_INCR(pPager->nMiss);
+pPg->pPager = pPager;
+if( sqlite3BitvecTest(pPager->pInJournal, pgno) ){
+assert( !MEMDB );
+pPg->flags |= PGHDR_IN_JOURNAL;
+}
+memset(pPg->pExtra, 0, pPager->nExtra);
+rc = sqlite3PagerPagecount(pPager, &nMax);
+if( rc!=SQLITE_OK ){
+sqlite3PagerUnref(pPg);
+return rc;
+}
+if( nMax<(int)pgno || MEMDB || noContent ){
+if( pgno>pPager->mxPgno ){
+sqlite3PagerUnref(pPg);
+return SQLITE_FULL;
+}
+memset(pPg->pData, 0, pPager->pageSize);
+if( noContent ){
+pPg->flags |= PGHDR_NEED_READ;
+}
+IOTRACE(("ZERO %p %d\n", pPager, pgno));
+}else{
+rc = readDbPage(pPager, pPg, pgno);
+if( rc!=SQLITE_OK && rc!=SQLITE_IOERR_SHORT_READ ){
+/* sqlite3PagerUnref(pPg); */
+pagerDropPage(pPg);
+return rc;
+}
+}
+#ifdef SQLITE_CHECK_PAGES
+pPg->pageHash = pager_pagehash(pPg);
+#endif
+}else{
+/* The requested page is in the page cache. */
+assert(sqlite3PcacheRefCount(pPager->pPCache)>0 || pgno==1);
+PAGER_INCR(pPager->nHit);
+if( !noContent ){
+rc = pager_get_content(pPg);
+if( rc ){
+sqlite3PagerUnref(pPg);
+return rc;
+}
+}
+}
+*ppPage = pPg;
+return SQLITE_OK;
+}
+/*
+** 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.
+**
+** 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 );
+if( (pPager->state!=PAGER_UNLOCK)
+&& (pPager->errCode==SQLITE_OK || pPager->errCode==SQLITE_FULL)
+){
+sqlite3PcacheFetch(pPager->pPCache, pgno, 0, &pPg);
+}
+return pPg;
+}
+/*
+** Release a page.
+**
+** 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.
+*/
+int sqlite3PagerUnref(DbPage *pPg){
+if( pPg ){
+Pager *pPager = pPg->pPager;
+sqlite3PcacheRelease(pPg);
+pagerUnlockIfUnused(pPager);
+}
+return SQLITE_OK;
+}
+/*
+** Create a journal file for pPager.  There should already be a RESERVED
+** or EXCLUSIVE lock on the database file when this routine is called.
+**
+** Return SQLITE_OK if everything.  Return an error code and release the
+** write lock if anything goes wrong.
+*/
+static int pager_open_journal(Pager *pPager){
+sqlite3_vfs *pVfs = pPager->pVfs;
+int flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_EXCLUSIVE|SQLITE_OPEN_CREATE);
+int rc;
+assert( !MEMDB );
+assert( pPager->state>=PAGER_RESERVED );
+assert( pPager->useJournal );
+assert( pPager->pInJournal==0 );
+sqlite3PagerPagecount(pPager, 0);
+pPager->pInJournal = sqlite3BitvecCreate(pPager->dbSize);
+if( pPager->pInJournal==0 ){
+rc = SQLITE_NOMEM;
+goto failed_to_open_journal;
+}
+if( pPager->journalOpen==0 ){
+if( pPager->tempFile ){
+flags |= (SQLITE_OPEN_DELETEONCLOSE|SQLITE_OPEN_TEMP_JOURNAL);
+}else{
+flags |= (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 || pPager->jfd->pMethods );
+pPager->journalOff = 0;
+pPager->setMaster = 0;
+pPager->journalHdr = 0;
+if( rc!=SQLITE_OK ){
+if( rc==SQLITE_NOMEM ){
+sqlite3OsDelete(pVfs, pPager->zJournal, 0);
+}
+goto failed_to_open_journal;
+}
+}
+pPager->journalOpen = 1;
+pPager->journalStarted = 0;
+pPager->needSync = 0;
+pPager->nRec = 0;
+if( pPager->errCode ){
+rc = pPager->errCode;
+goto failed_to_open_journal;
+}
+pPager->origDbSize = pPager->dbSize;
+rc = writeJournalHdr(pPager);
+if( pPager->stmtAutoopen && rc==SQLITE_OK ){
+rc = sqlite3PagerStmtBegin(pPager);
+}
+if( rc!=SQLITE_OK && rc!=SQLITE_NOMEM && rc!=SQLITE_IOERR_NOMEM ){
+rc = pager_end_transaction(pPager, 0);
+if( rc==SQLITE_OK ){
+rc = SQLITE_FULL;
+}
+}
+return rc;
+failed_to_open_journal:
+sqlite3BitvecDestroy(pPager->pInJournal);
+pPager->pInJournal = 0;
+return rc;
+}
+/*
+** Acquire a write-lock on the database.  The lock is removed when
+** the any of the following happen:
+**
+**   *  sqlite3PagerCommitPhaseTwo() is called.
+**   *  sqlite3PagerRollback() is called.
+**   *  sqlite3PagerClose() is called.
+**   *  sqlite3PagerUnref() is called to on every outstanding page.
+**
+** The first parameter to this routine is a pointer to any open page of the
+** database file.  Nothing changes about the page - it is used merely to
+** acquire a pointer to the Pager structure and as proof that there is
+** already a read-lock on the database.
+**
+** The second parameter indicates how much space in bytes to reserve for a
+** master journal file-name at the start of the journal when it is created.
+**
+** A journal file is opened if this is not a temporary file.  For temporary
+** files, the opening of the journal file is deferred until there is an
+** actual need to write to the journal.
+**
+** If the database is already reserved for writing, this routine is a no-op.
+**
+** If exFlag is true, go ahead and get an EXCLUSIVE lock on the file
+** immediately instead of waiting until we try to flush the cache.  The
+** exFlag is ignored if a transaction is already active.
+*/
+int sqlite3PagerBegin(DbPage *pPg, int exFlag){
+Pager *pPager = pPg->pPager;
+int rc = SQLITE_OK;
+assert( pPg->nRef>0 );
+assert( pPager->state!=PAGER_UNLOCK );
+if( pPager->state==PAGER_SHARED ){
+assert( pPager->pInJournal==0 );
+sqlite3PcacheAssertFlags(pPager->pPCache, 0, PGHDR_IN_JOURNAL);
+if( MEMDB ){
+pPager->state = PAGER_EXCLUSIVE;
+pPager->origDbSize = pPager->dbSize;
+}else{
+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( rc!=SQLITE_OK ){
+return rc;
+}
+pPager->dirtyCache = 0;
+PAGERTRACE2("TRANSACTION %d\n", PAGERID(pPager));
+if( pPager->useJournal && !pPager->tempFile
+&& pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
+rc = pager_open_journal(pPager);
+}
+}
+}else if( pPager->journalOpen && 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->origDbSize==0 );
+assert( pPager->pInJournal==0 );
+sqlite3PagerPagecount(pPager, 0);
+pPager->pInJournal = sqlite3BitvecCreate( pPager->dbSize );
+if( !pPager->pInJournal ){
+rc = SQLITE_NOMEM;
+}else{
+pPager->origDbSize = pPager->dbSize;
+rc = writeJournalHdr(pPager);
+}
+}
+assert( !pPager->journalOpen || pPager->journalOff>0 || rc!=SQLITE_OK );
+return rc;
+}
+/*
+** Make a page dirty.  Set its dirty flag and add it to the dirty
+** page list.
+*/
+static void makeDirty(PgHdr *pPg){
+sqlite3PcacheMakeDirty(pPg);
+}
+/*
+** Make a page clean.  Clear its dirty bit and remove it from the
+** dirty page list.
+*/
+static void makeClean(PgHdr *pPg){
+sqlite3PcacheMakeClean(pPg);
+}
+/*
+** Mark a data page as writeable.  The page is written into the journal
+** if it is not there already.  This routine must be called before making
+** changes to a page.
+**
+** The first time this routine is called, the pager creates a new
+** journal and acquires a RESERVED lock on the database.  If the RESERVED
+** lock could not be acquired, this routine returns SQLITE_BUSY.  The
+** calling routine must check for that return value and be careful not to
+** change any page data until this routine returns SQLITE_OK.
+**
+** If the journal file could not be written because the disk is full,
+** then this routine returns SQLITE_FULL and does an immediate rollback.
+** All subsequent write attempts also return SQLITE_FULL until there
+** is a call to sqlite3PagerCommit() or sqlite3PagerRollback() to
+** reset.
+*/
+static int pager_write(PgHdr *pPg){
+void *pData = pPg->pData;
+Pager *pPager = pPg->pPager;
+int rc = SQLITE_OK;
+/* Check for errors
+*/
+if( pPager->errCode ){
+return pPager->errCode;
+}
+if( pPager->readOnly ){
+return SQLITE_PERM;
+}
+assert( !pPager->setMaster );
+CHECK_PAGE(pPg);
+/* If this page was previously acquired with noContent==1, that means
+** we didn't really read in the content of the page.  This can happen
+** (for example) when the page is being moved to the freelist.  But
+** now we are (perhaps) moving the page off of the freelist for
+** reuse and we need to know its original content so that content
+** can be stored in the rollback journal.  So do the read at this
+** time.
+*/
+rc = pager_get_content(pPg);
+if( rc ){
+return rc;
+}
+/* Mark the page as dirty.  If the page has already been written
+** to the journal then we can return right away.
+*/
+makeDirty(pPg);
+if( (pPg->flags&PGHDR_IN_JOURNAL)
+&& (pageInStatement(pPg) || pPager->stmtInUse==0)
+){
+pPager->dirtyCache = 1;
+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.
+**
+** First check to see that the transaction journal exists and
+** create it if it does not.
+*/
+assert( pPager->state!=PAGER_UNLOCK );
+rc = sqlite3PagerBegin(pPg, 0);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+assert( pPager->state>=PAGER_RESERVED );
+if( !pPager->journalOpen && pPager->useJournal
+&& pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
+rc = pager_open_journal(pPager);
+if( rc!=SQLITE_OK ) return rc;
+}
+pPager->dirtyCache = 1;
+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( !(pPg->flags&PGHDR_IN_JOURNAL) && (pPager->journalOpen || MEMDB) ){
+if( (int)pPg->pgno <= pPager->origDbSize ){
+if( MEMDB ){
+PAGERTRACE3("JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
+rc = sqlite3PcachePreserve(pPg, 0);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+}else{
+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) );
+pData2 = CODEC2(pPager, pData, pPg->pgno, 7);
+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);
+PAGERTRACE5("JOURNAL %d page %d needSync=%d hash(%08x)\n",
+PAGERID(pPager), pPg->pgno,
+((pPg->flags&PGHDR_NEED_SYNC)?1:0), pager_pagehash(pPg));
+/* An error has occured 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 );
+sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);
+if( !pPager->noSync ){
+pPg->flags |= PGHDR_NEED_SYNC;
+}
+if( pPager->stmtInUse ){
+sqlite3BitvecSet(pPager->pInStmt, pPg->pgno);
+}
+}
+}else{
+if( !pPager->journalStarted && !pPager->noSync ){
+pPg->flags |= PGHDR_NEED_SYNC;
+}
+PAGERTRACE4("APPEND %d page %d needSync=%d\n",
+PAGERID(pPager), pPg->pgno,
+((pPg->flags&PGHDR_NEED_SYNC)?1:0));
+}
+if( pPg->flags&PGHDR_NEED_SYNC ){
+pPager->needSync = 1;
+}
+pPg->flags |= PGHDR_IN_JOURNAL;
+}
+/* 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( pPager->stmtInUse
+&& !pageInStatement(pPg)
+&& (int)pPg->pgno<=pPager->stmtSize
+){
+assert( (pPg->flags&PGHDR_IN_JOURNAL)
+|| (int)pPg->pgno>pPager->origDbSize );
+if( MEMDB ){
+rc = sqlite3PcachePreserve(pPg, 1);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+PAGERTRACE3("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
+}else{
+i64 offset = pPager->stmtNRec*(4+pPager->pageSize);
+char *pData2 = CODEC2(pPager, pData, pPg->pgno, 7);
+rc = write32bits(pPager->stfd, offset, pPg->pgno);
+if( rc==SQLITE_OK ){
+rc = sqlite3OsWrite(pPager->stfd, pData2, pPager->pageSize, offset+4);
+}
+PAGERTRACE3("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+pPager->stmtNRec++;
+assert( pPager->pInStmt!=0 );
+sqlite3BitvecSet(pPager->pInStmt, pPg->pgno);
+}
+}
+}
+/* Update the database size and return.
+*/
+assert( pPager->state>=PAGER_SHARED );
+if( pPager->dbSize<(int)pPg->pgno ){
+pPager->dbSize = pPg->pgno;
+if( !MEMDB && pPager->dbSize==PENDING_BYTE/pPager->pageSize ){
+pPager->dbSize++;
+}
+}
+return rc;
+}
+/*
+** This function is used to mark a data-page as writable. It uses
+** pager_write() to open a journal file (if it is not already open)
+** and write the page *pData to the journal.
+**
+** 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.
+*/
+int sqlite3PagerWrite(DbPage *pDbPage){
+int rc = SQLITE_OK;
+PgHdr *pPg = pDbPage;
+Pager *pPager = pPg->pPager;
+Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);
+if( !MEMDB && 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;
+int needSync = 0;
+/* 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( 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;
+}
+sqlite3PagerUnref(pPage);
+}
+}
+}else if( (pPage = pager_lookup(pPager, pg))!=0 ){
+if( pPage->flags&PGHDR_NEED_SYNC ){
+needSync = 1;
+}
+sqlite3PagerUnref(pPage);
+}
+}
+/* If the PgHdr.needSync 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( needSync ){
+assert( !MEMDB && pPager->noSync==0 );
+for(ii=0; ii<nPage && needSync; 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.
+**
+** 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, together with the
+** sqlite3PagerDontRollback() below, more than double the speed
+** of large INSERT operations and quadruple the speed of large DELETEs.
+**
+** When this routine is called, set the alwaysRollback flag to true.
+** Subsequent calls to sqlite3PagerDontRollback() for the same page
+** will thereafter be ignored.  This is necessary to avoid a problem
+** where a page with data is added to the freelist during one part of
+** a transaction then removed from the freelist during a later part
+** of the same transaction and reused for some other purpose.  When it
+** is first added to the freelist, this routine is called.  When reused,
+** the sqlite3PagerDontRollback() routine is called.  But because the
+** page contains critical data, we still need to be sure it gets
+** rolled back in spite of the sqlite3PagerDontRollback() call.
+*/
+int sqlite3PagerDontWrite(DbPage *pDbPage){
+PgHdr *pPg = pDbPage;
+Pager *pPager = pPg->pPager;
+int rc;
+if( MEMDB || pPg->pgno>pPager->origDbSize ){
+return SQLITE_OK;
+}
+if( pPager->pAlwaysRollback==0 ){
+assert( pPager->pInJournal );
+pPager->pAlwaysRollback = sqlite3BitvecCreate(pPager->origDbSize);
+if( !pPager->pAlwaysRollback ){
+return SQLITE_NOMEM;
+}
+}
+rc = sqlite3BitvecSet(pPager->pAlwaysRollback, pPg->pgno);
+if( rc==SQLITE_OK && (pPg->flags&PGHDR_DIRTY) && !pPager->stmtInUse ){
+assert( pPager->state>=PAGER_SHARED );
+if( pPager->dbSize==(int)pPg->pgno && pPager->origDbSize<pPager->dbSize ){
+/* If this pages is the last page in the file and the file has grown
+** during the current transaction, then do NOT mark the page as clean.
+** When the database file grows, we must make sure that the last page
+** gets written at least once so that the disk file will be the correct
+** size. If you do not write this page and the size of the file
+** on the disk ends up being too small, that can lead to database
+** corruption during the next transaction.
+*/
+}else{
+PAGERTRACE3("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
+}
+}
+return rc;
+}
+/*
+** A call to this routine tells the pager that if a rollback occurs,
+** it is not necessary to restore the data on the given page.  This
+** means that the pager does not have to record the given page in the
+** rollback journal.
+**
+** If we have not yet actually read the content of this page (if
+** the PgHdr.needRead flag is set) then this routine acts as a promise
+** that we will never need to read the page content in the future.
+** so the needRead flag can be cleared at this point.
+*/
+void sqlite3PagerDontRollback(DbPage *pPg){
+Pager *pPager = pPg->pPager;
+assert( pPager->state>=PAGER_RESERVED );
+/* If the journal file is not open, or DontWrite() has been called on
+** this page (DontWrite() sets the alwaysRollback flag), then this
+** function is a no-op.
+*/
+if( pPager->journalOpen==0
+|| sqlite3BitvecTest(pPager->pAlwaysRollback, pPg->pgno)
+|| pPg->pgno>pPager->origDbSize
+){
+return;
+}
+assert( !MEMDB );    /* For a memdb, pPager->journalOpen is always 0 */
+#ifdef SQLITE_SECURE_DELETE
+if( (pPg->flags & PGHDR_IN_JOURNAL)!=0 || (int)pPg->pgno>pPager->origDbSize ){
+return;
+}
+#endif
+/* If SECURE_DELETE is disabled, then there is no way that this
+** routine can be called on a page for which sqlite3PagerDontWrite()
+** has not been previously called during the same transaction.
+** And if DontWrite() has previously been called, the following
+** conditions must be met.
+**
+** (Later:)  Not true.  If the database is corrupted by having duplicate
+** pages on the freelist (ex: corrupt9.test) then the following is not
+** necessarily true:
+*/
+/* assert( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ); */
+assert( pPager->pInJournal!=0 );
+sqlite3BitvecSet(pPager->pInJournal, pPg->pgno);
+pPg->flags |= PGHDR_IN_JOURNAL;
+pPg->flags &= ~PGHDR_NEED_READ;
+if( pPager->stmtInUse ){
+assert( pPager->stmtSize >= pPager->origDbSize );
+sqlite3BitvecSet(pPager->pInStmt, pPg->pgno);
+}
+PAGERTRACE3("DONT_ROLLBACK page %d of %d\n", pPg->pgno, PAGERID(pPager));
+IOTRACE(("GARBAGE %p %d\n", pPager, pPg->pgno))
+}
+/*
+** This routine is called to increment the database file change-counter,
+** stored at byte 24 of the pager file.
+*/
+static int pager_incr_changecounter(Pager *pPager, int isDirect){
+PgHdr *pPgHdr;
+u32 change_counter;
+int rc = SQLITE_OK;
+#ifndef SQLITE_ENABLE_ATOMIC_WRITE
+assert( isDirect==0 );  /* isDirect is only true for atomic writes */
+#endif
+if( !pPager->changeCountDone ){
+/* Open page 1 of the file for writing. */
+rc = sqlite3PagerGet(pPager, 1, &pPgHdr);
+if( rc!=SQLITE_OK ) return rc;
+if( !isDirect ){
+rc = sqlite3PagerWrite(pPgHdr);
+if( rc!=SQLITE_OK ){
+sqlite3PagerUnref(pPgHdr);
+return rc;
+}
+}
+/* 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);
+#ifdef SQLITE_ENABLE_ATOMIC_WRITE
+if( isDirect && pPager->fd->pMethods ){
+const void *zBuf = pPgHdr->pData;
+rc = sqlite3OsWrite(pPager->fd, zBuf, pPager->pageSize, 0);
+}
+#endif
+/* Release the page reference. */
+sqlite3PagerUnref(pPgHdr);
+pPager->changeCountDone = 1;
+}
+return rc;
+}
+/*
+** Sync the pager file to disk.
+*/
+int sqlite3PagerSync(Pager *pPager){
+int rc;
+if( MEMDB ){
+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 journal is synced, all dirty pages written
+** to the database file and the database file synced. The only thing that
+** remains to commit the transaction is to delete the journal file (or
+** master journal file if specified).
+**
+** Note that if zMaster==NULL, this does not overwrite a previous value
+** passed to an sqlite3PagerCommitPhaseOne() call.
+**
+** If parameter nTrunc is non-zero, then the pager file is truncated to
+** nTrunc pages (this is used by auto-vacuum databases).
+**
+** 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,
+const char *zMaster,
+Pgno nTrunc,
+int noSync
+){
+int rc = SQLITE_OK;
+if( pPager->errCode ){
+return pPager->errCode;
+}
+/* If no changes have been made, we can leave the transaction early.
+*/
+if( pPager->dbModified==0 &&
+(pPager->journalMode!=PAGER_JOURNALMODE_DELETE ||
+pPager->exclusiveMode!=0) ){
+assert( pPager->dirtyCache==0 || pPager->journalOpen==0 );
+return SQLITE_OK;
+}
+PAGERTRACE4("DATABASE SYNC: File=%s zMaster=%s nTrunc=%d\n",
+pPager->zFilename, zMaster, nTrunc);
+/* If this is an in-memory db, or no pages have been written to, or this
+** function has already been called, it is a no-op.
+*/
+if( pPager->state!=PAGER_SYNCED && !MEMDB && pPager->dirtyCache ){
+PgHdr *pPg;
+#ifdef SQLITE_ENABLE_ATOMIC_WRITE
+/* The atomic-write optimization can be used if all of the
+** following are true:
+**
+**    + 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 can be used, then the journal file will never
+** be created for this transaction.
+*/
+int useAtomicWrite;
+pPg = sqlite3PcacheDirtyList(pPager->pPCache);
+useAtomicWrite = (
+!zMaster &&
+pPager->journalOpen &&
+pPager->journalOff==jrnlBufferSize(pPager) &&
+nTrunc==0 &&
+(pPg==0 || pPg->pDirty==0)
+);
+assert( pPager->journalOpen || pPager->journalMode==PAGER_JOURNALMODE_OFF );
+if( useAtomicWrite ){
+/* Update the nRec field in the journal file. */
+int offset = pPager->journalHdr + sizeof(aJournalMagic);
+assert(pPager->nRec==1);
+rc = write32bits(pPager->jfd, offset, pPager->nRec);
+/* Update the db file change counter. 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.
+*/
+if( rc==SQLITE_OK ){
+rc = pager_incr_changecounter(pPager, 1);
+}
+}else{
+rc = sqlite3JournalCreate(pPager->jfd);
+}
+if( !useAtomicWrite && rc==SQLITE_OK )
+#endif
+/* If a master journal file name has already been written to the
+** journal file, then no sync is required. This happens when it is
+** written, then the process fails to upgrade from a RESERVED to an
+** EXCLUSIVE lock. The next time the process tries to commit the
+** transaction the m-j name will have already been written.
+*/
+if( !pPager->setMaster ){
+rc = pager_incr_changecounter(pPager, 0);
+if( rc!=SQLITE_OK ) goto sync_exit;
+if( pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
+#ifndef SQLITE_OMIT_AUTOVACUUM
+if( nTrunc!=0 ){
+/* If this transaction has made the database smaller, then all pages
+** being discarded by the truncation must be written to the journal
+** file.
+*/
+Pgno i;
+int iSkip = PAGER_MJ_PGNO(pPager);
+for( i=nTrunc+1; i<=pPager->origDbSize; i++ ){
+if( !sqlite3BitvecTest(pPager->pInJournal, i) && i!=iSkip ){
+rc = sqlite3PagerGet(pPager, i, &pPg);
+if( rc!=SQLITE_OK ) goto sync_exit;
+rc = sqlite3PagerWrite(pPg);
+sqlite3PagerUnref(pPg);
+if( rc!=SQLITE_OK ) goto sync_exit;
+}
+}
+}
+#endif
+rc = writeMasterJournal(pPager, zMaster);
+if( rc!=SQLITE_OK ) goto sync_exit;
+rc = syncJournal(pPager);
+}
+}
+if( rc!=SQLITE_OK ) goto sync_exit;
+#ifndef SQLITE_OMIT_AUTOVACUUM
+if( nTrunc!=0 ){
+rc = sqlite3PagerTruncate(pPager, nTrunc);
+if( rc!=SQLITE_OK ) goto sync_exit;
+}
+#endif
+/* Write all dirty pages to the database file */
+pPg = sqlite3PcacheDirtyList(pPager->pPCache);
+rc = pager_write_pagelist(pPg);
+if( rc!=SQLITE_OK ){
+assert( rc!=SQLITE_IOERR_BLOCKED );
+/* The error might have left the dirty list all fouled up here,
+** but that does not matter because if the if the dirty list did
+** get corrupted, then the transaction will roll back and
+** discard the dirty list.  There is an assert in
+** pager_get_all_dirty_pages() that verifies that no attempt
+** is made to use an invalid dirty list.
+*/
+goto sync_exit;
+}
+sqlite3PcacheCleanAll(pPager->pPCache);
+/* Sync the database file. */
+if( !pPager->noSync && !noSync ){
+rc = sqlite3OsSync(pPager->fd, pPager->sync_flags);
+}
+IOTRACE(("DBSYNC %p\n", pPager))
+pPager->state = PAGER_SYNCED;
+}else if( MEMDB && nTrunc!=0 ){
+rc = sqlite3PagerTruncate(pPager, nTrunc);
+}
+sync_exit:
+if( rc==SQLITE_IOERR_BLOCKED ){
+/* pager_incr_changecounter() may attempt to obtain an exclusive
+* lock to spill the cache and return IOERR_BLOCKED. But since
+* there is no chance the cache is inconsistent, it is
+* better to return SQLITE_BUSY.
+*/
+rc = SQLITE_BUSY;
+}
+return rc;
+}
+/*
+** Commit all changes to the database and release the write lock.
+**
+** If the commit fails for any reason, a rollback attempt is made
+** and an error code is returned.  If the commit worked, SQLITE_OK
+** is returned.
+*/
+int sqlite3PagerCommitPhaseTwo(Pager *pPager){
+int rc = SQLITE_OK;
+if( pPager->errCode ){
+return pPager->errCode;
+}
+if( pPager->state<PAGER_RESERVED ){
+return SQLITE_ERROR;
+}
+if( pPager->dbModified==0 &&
+(pPager->journalMode!=PAGER_JOURNALMODE_DELETE ||
+pPager->exclusiveMode!=0) ){
+assert( pPager->dirtyCache==0 || pPager->journalOpen==0 );
+return SQLITE_OK;
+}
+PAGERTRACE2("COMMIT %d\n", PAGERID(pPager));
+if( MEMDB ){
+sqlite3PcacheCommit(pPager->pPCache, 0);
+sqlite3PcacheCleanAll(pPager->pPCache);
+sqlite3PcacheAssertFlags(pPager->pPCache, 0, PGHDR_IN_JOURNAL);
+pPager->state = PAGER_SHARED;
+}else{
+assert( pPager->state==PAGER_SYNCED || !pPager->dirtyCache );
+rc = pager_end_transaction(pPager, pPager->setMaster);
+rc = pager_error(pPager, rc);
+}
+return rc;
+}
+/*
+** Rollback all changes.  The database falls back to PAGER_SHARED mode.
+** All in-memory cache pages revert to their original data contents.
+** The journal is deleted.
+**
+** This routine cannot fail unless some other process is not following
+** the correct locking protocol or unless some other
+** process is writing trash into the journal file (SQLITE_CORRUPT) or
+** unless a prior malloc() failed (SQLITE_NOMEM).  Appropriate error
+** codes are returned for all these occasions.  Otherwise,
+** SQLITE_OK is returned.
+*/
+int sqlite3PagerRollback(Pager *pPager){
+int rc = SQLITE_OK;
+PAGERTRACE2("ROLLBACK %d\n", PAGERID(pPager));
+if( MEMDB ){
+sqlite3PcacheRollback(pPager->pPCache, 1, pPager->xReiniter);
+sqlite3PcacheRollback(pPager->pPCache, 0, pPager->xReiniter);
+sqlite3PcacheCleanAll(pPager->pPCache);
+sqlite3PcacheAssertFlags(pPager->pPCache, 0, PGHDR_IN_JOURNAL);
+pPager->dbSize = pPager->origDbSize;
+pager_truncate_cache(pPager);
+pPager->stmtInUse = 0;
+pPager->state = PAGER_SHARED;
+}else if( !pPager->dirtyCache || !pPager->journalOpen ){
+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);
+}
+pPager->dbSize = -1;
+/* 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.
+*/
+int 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->dbSize;
+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;
+}
+int sqlite3PagerIsMemdb(Pager *pPager){
+return MEMDB;
+}
+#endif
+/*
+** Set the statement rollback point.
+**
+** This routine should be called with the transaction journal already
+** open.  A new statement journal is created that can be used to rollback
+** changes of a single SQL command within a larger transaction.
+*/
+static int pagerStmtBegin(Pager *pPager){
+int rc;
+assert( !pPager->stmtInUse );
+assert( pPager->state>=PAGER_SHARED );
+assert( pPager->dbSize>=0 );
+PAGERTRACE2("STMT-BEGIN %d\n", PAGERID(pPager));
+if( MEMDB ){
+pPager->stmtInUse = 1;
+pPager->stmtSize = pPager->dbSize;
+return SQLITE_OK;
+}
+if( !pPager->journalOpen ){
+pPager->stmtAutoopen = 1;
+return SQLITE_OK;
+}
+assert( pPager->journalOpen );
+assert( pPager->pInStmt==0 );
+pPager->pInStmt = sqlite3BitvecCreate(pPager->dbSize);
+if( pPager->pInStmt==0 ){
+/* sqlite3OsLock(pPager->fd, SHARED_LOCK); */
+return SQLITE_NOMEM;
+}
+pPager->stmtJSize = pPager->journalOff;
+pPager->stmtSize = pPager->dbSize;
+pPager->stmtHdrOff = 0;
+pPager->stmtCksum = pPager->cksumInit;
+if( !pPager->stmtOpen ){
+rc = sqlite3PagerOpentemp(pPager, pPager->stfd, SQLITE_OPEN_SUBJOURNAL);
+if( rc ){
+goto stmt_begin_failed;
+}
+pPager->stmtOpen = 1;
+pPager->stmtNRec = 0;
+}
+pPager->stmtInUse = 1;
+return SQLITE_OK;
+stmt_begin_failed:
+if( pPager->pInStmt ){
+sqlite3BitvecDestroy(pPager->pInStmt);
+pPager->pInStmt = 0;
+}
+return rc;
+}
+int sqlite3PagerStmtBegin(Pager *pPager){
+int rc;
+rc = pagerStmtBegin(pPager);
+return rc;
+}
+/*
+** Commit a statement.
+*/
+int sqlite3PagerStmtCommit(Pager *pPager){
+if( pPager->stmtInUse ){
+PAGERTRACE2("STMT-COMMIT %d\n", PAGERID(pPager));
+if( !MEMDB ){
+sqlite3BitvecDestroy(pPager->pInStmt);
+pPager->pInStmt = 0;
+}else{
+sqlite3PcacheCommit(pPager->pPCache, 1);
+}
+pPager->stmtNRec = 0;
+pPager->stmtInUse = 0;
+}
+pPager->stmtAutoopen = 0;
+return SQLITE_OK;
+}
+/*
+** Rollback a statement.
+*/
+int sqlite3PagerStmtRollback(Pager *pPager){
+int rc;
+if( pPager->stmtInUse ){
+PAGERTRACE2("STMT-ROLLBACK %d\n", PAGERID(pPager));
+if( MEMDB ){
+sqlite3PcacheRollback(pPager->pPCache, 1, pPager->xReiniter);
+pPager->dbSize = pPager->stmtSize;
+pager_truncate_cache(pPager);
+rc = SQLITE_OK;
+}else{
+rc = pager_stmt_playback(pPager);
+}
+sqlite3PagerStmtCommit(pPager);
+}else{
+rc = SQLITE_OK;
+}
+pPager->stmtAutoopen = 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 directory of the database file.
+*/
+const char *sqlite3PagerDirname(Pager *pPager){
+return pPager->zDirectory;
+}
+/*
+** 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 the codec for this pager
+*/
+void sqlite3PagerSetCodec(
+Pager *pPager,
+void *(*xCodec)(void*,void*,Pgno,int),
+void *pCodecArg
+){
+pPager->xCodec = xCodec;
+pPager->pCodecArg = pCodecArg;
+}
+#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.
+*/
+int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno, int isCommit){
+PgHdr *pPgOld;  /* The page being overwritten. */
+Pgno needSyncPgno = 0;
+assert( pPg->nRef>0 );
+PAGERTRACE5("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))
+pager_get_content(pPg);
+/* 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( (pPg->flags&PGHDR_IN_JOURNAL) || (int)pgno>pPager->origDbSize );
+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|PGHDR_IN_JOURNAL);
+pPgOld = pager_lookup(pPager, pgno);
+assert( !pPgOld || pPgOld->nRef==1 );
+if( pPgOld ){
+pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
+}
+if( sqlite3BitvecTest(pPager->pInJournal, pgno) ){
+assert( !MEMDB );
+pPg->flags |= PGHDR_IN_JOURNAL;
+}
+sqlite3PcacheMove(pPg, pgno);
+if( pPgOld ){
+sqlite3PcacheMove(pPgOld, 0);
+sqlite3PcacheRelease(pPgOld);
+}
+makeDirty(pPg);
+pPager->dirtyCache = 1;
+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.
+*/
+int rc;
+PgHdr *pPgHdr;
+assert( pPager->needSync );
+rc = sqlite3PagerGet(pPager, needSyncPgno, &pPgHdr);
+if( rc!=SQLITE_OK ){
+if( pPager->pInJournal && (int)needSyncPgno<=pPager->origDbSize ){
+sqlite3BitvecClear(pPager->pInJournal, needSyncPgno);
+}
+return rc;
+}
+pPager->needSync = 1;
+assert( pPager->noSync==0 && !MEMDB );
+pPgHdr->flags |= PGHDR_NEED_SYNC;
+pPgHdr->flags |= PGHDR_IN_JOURNAL;
+makeDirty(pPgHdr);
+sqlite3PagerUnref(pPgHdr);
+}
+return SQLITE_OK;
+}
+#endif
+/*
+** 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){
+Pager *pPager = pPg->pPager;
+return (pPager?pPg->pExtra:0);
+}
+/*
+** 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 = 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
+**
+** If the parameter is not _QUERY, then the journal-mode is set to the
+** value specified.
+**
+** 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 );
+assert( PAGER_JOURNALMODE_QUERY<0 );
+if( eMode>=0 ){
+pPager->journalMode = eMode;
+}else{
+assert( eMode==PAGER_JOURNALMODE_QUERY );
+}
+return (int)pPager->journalMode;
+}
+/*
+** Get/set the size-limit used for persistent journal files.
+*/
+i64 sqlite3PagerJournalSizeLimit(Pager *pPager, i64 iLimit){
+if( iLimit>=-1 ){
+pPager->journalSizeLimit = iLimit;
+}
+return pPager->journalSizeLimit;
+}
+#endif /* SQLITE_OMIT_DISKIO */