MCL/sf/mw/web: comparison webengine/webkitutils/SqliteSymbian/pager.c

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--1:000000000000
+:dd21522fd290
+/*
+** 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 1.271 2006/08/08 13:51:43 drh Exp $
+*/
+#ifndef SQLITE_OMIT_DISKIO
+#include "sqliteInt.h"
+#include "os.h"
+#include "pager.h"
+#include <assert.h>
+#include <string.h>
+/*
+** Macros for troubleshooting.  Normally turned off
+*/
+#if 0
+#define TRACE1(X)       sqlite3DebugPrintf(X)
+#define TRACE2(X,Y)     sqlite3DebugPrintf(X,Y)
+#define TRACE3(X,Y,Z)   sqlite3DebugPrintf(X,Y,Z)
+#define TRACE4(X,Y,Z,W) sqlite3DebugPrintf(X,Y,Z,W)
+#define TRACE5(X,Y,Z,W,V) sqlite3DebugPrintf(X,Y,Z,W,V)
+#else
+#define TRACE1(X)
+#define TRACE2(X,Y)
+#define TRACE3(X,Y,Z)
+#define TRACE4(X,Y,Z,W)
+#define TRACE5(X,Y,Z,W,V)
+#endif
+/*
+** The following two macros are used within the TRACEX() macros above
+** to print out file-descriptors.
+**
+** PAGERID() takes a pointer to a Pager struct as it's argument. The
+** associated file-descriptor is returned. FILEHANDLEID() takes an OsFile
+** struct as it's 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 the
+**                       journal file and the transaction will be
+**                       committed.
+**
+** The page cache comes up in PAGER_UNLOCK.  The first time a
+** sqlite3pager_get() 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 sqlite3pager_write() is called, the state transitions to
+** PAGER_RESERVED.  (Note that sqlite_page_write() can only be
+** called on an outstanding page which means that the pager must
+** be in PAGER_SHARED before it transitions to PAGER_RESERVED.)
+** The transition to PAGER_EXCLUSIVE occurs when before any changes
+** are made to the database file.  After an sqlite3pager_rollback()
+** or sqlite_pager_commit(), the state goes back to PAGER_SHARED.
+*/
+#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)
+/*
+** Each in-memory image of a page begins with the following header.
+** This header is only visible to this pager module.  The client
+** code that calls pager sees only the data that follows the header.
+**
+** Client code should call sqlite3pager_write() on a page prior to making
+** any modifications to that page.  The first time sqlite3pager_write()
+** is called, the original page contents are written into the rollback
+** journal and PgHdr.inJournal and PgHdr.needSync are set.  Later, once
+** the journal page has made it onto the disk surface, PgHdr.needSync
+** is cleared.  The modified page cannot be written back into the original
+** database file until the journal pages has been synced to disk and the
+** PgHdr.needSync has been cleared.
+**
+** The PgHdr.dirty flag is set when sqlite3pager_write() is called and
+** is cleared again when the page content is written back to the original
+** database file.
+*/
+typedef struct PgHdr PgHdr;
+struct PgHdr {
+Pager *pPager;                 /* The pager to which this page belongs */
+Pgno pgno;                     /* The page number for this page */
+PgHdr *pNextHash, *pPrevHash;  /* Hash collision chain for PgHdr.pgno */
+PgHdr *pNextFree, *pPrevFree;  /* Freelist of pages where nRef==0 */
+PgHdr *pNextAll;               /* A list of all pages */
+PgHdr *pNextStmt, *pPrevStmt;  /* List of pages in the statement journal */
+u8 inJournal;                  /* TRUE if has been written to journal */
+u8 inStmt;                     /* TRUE if in the statement subjournal */
+u8 dirty;                      /* TRUE if we need to write back changes */
+u8 needSync;                   /* Sync journal before writing this page */
+u8 alwaysRollback;             /* Disable dont_rollback() for this page */
+short int nRef;                /* Number of users of this page */
+PgHdr *pDirty, *pPrevDirty;    /* Dirty pages */
+u32 notUsed;                   /* Buffer space */
+#ifdef SQLITE_CHECK_PAGES
+u32 pageHash;
+#endif
+/* pPager->pageSize bytes of page data follow this header */
+/* Pager.nExtra bytes of local data follow the page data */
+};
+/*
+** For an in-memory only database, some extra information is recorded about
+** each page so that changes can be rolled back.  (Journal files are not
+** used for in-memory databases.)  The following information is added to
+** the end of every EXTRA block for in-memory databases.
+**
+** This information could have been added directly to the PgHdr structure.
+** But then it would take up an extra 8 bytes of storage on every PgHdr
+** even for disk-based databases.  Splitting it out saves 8 bytes.  This
+** is only a savings of 0.8% but those percentages add up.
+*/
+typedef struct PgHistory PgHistory;
+struct PgHistory {
+u8 *pOrig;     /* Original page text.  Restore to this on a full rollback */
+u8 *pStmt;     /* Text as it was at the beginning of the current statement */
+};
+/*
+** 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
+/*
+** Convert a pointer to a PgHdr into a pointer to its data
+** and back again.
+*/
+#define PGHDR_TO_DATA(P)  ((void*)(&(P)[1]))
+#define DATA_TO_PGHDR(D)  (&((PgHdr*)(D))[-1])
+#define PGHDR_TO_EXTRA(G,P) ((void*)&((char*)(&(G)[1]))[(P)->pageSize])
+#define PGHDR_TO_HIST(P,PGR)  \
+((PgHistory*)&((char*)(&(P)[1]))[(PGR)->pageSize+(PGR)->nExtra])
+/*
+** A open page cache is an instance of the following structure.
+**
+** Pager.errCode may be set to SQLITE_IOERR, SQLITE_CORRUPT, SQLITE_PROTOCOL
+** 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 sqlite3pager_get() and sqlite3pager_lookup()
+** APIs, they may still be used successfully.
+*/
+struct Pager {
+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 full_fsync;              /* Use F_FULLFSYNC when available */
+u8 state;                   /* PAGER_UNLOCK, _SHARED, _RESERVED, etc. */
+u8 errCode;                 /* One of several kinds of errors */
+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 dont_rollback() 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 */
+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 nMaxPage;               /* High water mark of nPage */
+int nRef;                   /* Number of in-memory pages with PgHdr.nRef>0 */
+int mxPage;                 /* Maximum number of pages to hold in cache */
+u8 *aInJournal;             /* One bit for each page in the database file */
+u8 *aInStmt;                /* One bit for each page in the database */
+char *zFilename;            /* Name of the database file */
+char *zJournal;             /* Name of the journal file */
+char *zDirectory;           /* Directory hold database and journal files */
+OsFile *fd, *jfd;           /* File descriptors for database and journal */
+OsFile *stfd;               /* File descriptor for the statement subjournal*/
+BusyHandler *pBusyHandler;  /* Pointer to sqlite.busyHandler */
+PgHdr *pFirst, *pLast;      /* List of free pages */
+PgHdr *pFirstSynced;        /* First free page with PgHdr.needSync==0 */
+PgHdr *pAll;                /* List of all pages */
+PgHdr *pStmt;               /* List of pages in the statement subjournal */
+PgHdr *pDirty;              /* List of all dirty pages */
+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, nOvfl;     /* Cache hits, missing, and LRU overflows */
+int nRead,nWrite;           /* Database pages read/written */
+#endif
+void (*xDestructor)(void*,int); /* Call this routine when freeing pages */
+void (*xReiniter)(void*,int);   /* Call this routine when reloading pages */
+void *(*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
+void *pCodecArg;            /* First argument to xCodec() */
+int nHash;                  /* Size of the pager hash table */
+PgHdr **aHash;              /* Hash table to map page number to PgHdr */
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+Pager *pNext;               /* Linked list of pagers in this thread */
+#endif
+};
+/*
+** If SQLITE_TEST is defined then increment the variable given in
+** the argument
+*/
+#ifdef SQLITE_TEST
+# define TEST_INCR(x)  x++
+#else
+# define TEST_INCR(x)
+#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
+/*
+** The default size of a disk sector
+*/
+#define PAGER_SECTOR_SIZE 512
+/*
+** 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
+/*
+** Enable reference count tracking (for debugging) here:
+*/
+#ifdef SQLITE_TEST
+int pager3_refinfo_enable = 0;
+static void pager_refinfo(PgHdr *p){
+static int cnt = 0;
+if( !pager3_refinfo_enable ) return;
+sqlite3DebugPrintf(
+"REFCNT: %4d addr=%p nRef=%d\n",
+p->pgno, PGHDR_TO_DATA(p), p->nRef
+);
+cnt++;   /* Something to set a breakpoint on */
+}
+# define REFINFO(X)  pager_refinfo(X)
+#else
+# define REFINFO(X)
+#endif
+/*
+** Change the size of the pager hash table to N.  N must be a power
+** of two.
+*/
+static void pager_resize_hash_table(Pager *pPager, int N){
+PgHdr **aHash, *pPg;
+assert( N>0 && (N&(N-1))==0 );
+aHash = sqliteMalloc( sizeof(aHash[0])*N );
+if( aHash==0 ){
+/* Failure to rehash is not an error.  It is only a performance hit. */
+return;
+}
+sqliteFree(pPager->aHash);
+pPager->nHash = N;
+pPager->aHash = aHash;
+for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
+int h;
+if( pPg->pgno==0 ){
+assert( pPg->pNextHash==0 && pPg->pPrevHash==0 );
+continue;
+}
+h = pPg->pgno & (N-1);
+pPg->pNextHash = aHash[h];
+if( aHash[h] ){
+aHash[h]->pPrevHash = pPg;
+}
+aHash[h] = pPg;
+pPg->pPrevHash = 0;
+}
+}
+/*
+** 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(OsFile *fd, u32 *pRes){
+unsigned char ac[4];
+int rc = sqlite3OsRead(fd, ac, sizeof(ac));
+if( rc==SQLITE_OK ){
+*pRes = (ac[0]<<24) | (ac[1]<<16) | (ac[2]<<8) | ac[3];
+}
+return rc;
+}
+/*
+** Write a 32-bit integer into a string buffer in big-endian byte order.
+*/
+static void put32bits(char *ac, u32 val){
+ac[0] = (val>>24) & 0xff;
+ac[1] = (val>>16) & 0xff;
+ac[2] = (val>>8) & 0xff;
+ac[3] = val & 0xff;
+}
+/*
+** 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(OsFile *fd, u32 val){
+char ac[4];
+put32bits(ac, val);
+return sqlite3OsWrite(fd, ac, 4);
+}
+/*
+** Read a 32-bit integer at offset 'offset' from the page identified by
+** page header 'p'.
+*/
+static u32 retrieve32bits(PgHdr *p, int offset){
+unsigned char *ac;
+ac = &((unsigned char*)PGHDR_TO_DATA(p))[offset];
+return (ac[0]<<24) | (ac[1]<<16) | (ac[2]<<8) | ac[3];
+}
+/*
+** 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_PROTOCOL,
+** the error becomes persistent. All subsequent API calls on this Pager
+** will immediately return the same error code.
+*/
+static int pager_error(Pager *pPager, int rc){
+assert( pPager->errCode==SQLITE_FULL || pPager->errCode==SQLITE_OK );
+if(
+rc==SQLITE_FULL ||
+rc==SQLITE_IOERR ||
+rc==SQLITE_CORRUPT ||
+rc==SQLITE_PROTOCOL
+){
+pPager->errCode = rc;
+}
+return rc;
+}
+#ifdef SQLITE_CHECK_PAGES
+/*
+** Return a 32-bit hash of the page data for pPage.
+*/
+static u32 pager_pagehash(PgHdr *pPage){
+u32 hash = 0;
+int i;
+unsigned char *pData = (unsigned char *)PGHDR_TO_DATA(pPage);
+for(i=0; i<pPage->pPager->pageSize; i++){
+hash = (hash+i)^pData[i];
+}
+return hash;
+}
+/*
+** 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->dirty ||
+pPg->pageHash==pager_pagehash(pPg) );
+}
+#else
+#define CHECK_PAGE(x)
+#endif
+/*
+** 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 obtained from sqliteMalloc(). *pzMaster is
+** set to point at the memory and SQLITE_OK returned. The caller must
+** sqliteFree() *pzMaster.
+**
+** If no master journal file name is present *pzMaster is set to 0 and
+** SQLITE_OK returned.
+*/
+static int readMasterJournal(OsFile *pJrnl, char **pzMaster){
+int rc;
+u32 len;
+i64 szJ;
+u32 cksum;
+int i;
+unsigned char aMagic[8]; /* A buffer to hold the magic header */
+*pzMaster = 0;
+rc = sqlite3OsFileSize(pJrnl, &szJ);
+if( rc!=SQLITE_OK || szJ<16 ) return rc;
+rc = sqlite3OsSeek(pJrnl, szJ-16);
+if( rc!=SQLITE_OK ) return rc;
+rc = read32bits(pJrnl, &len);
+if( rc!=SQLITE_OK ) return rc;
+rc = read32bits(pJrnl, &cksum);
+if( rc!=SQLITE_OK ) return rc;
+rc = sqlite3OsRead(pJrnl, aMagic, 8);
+if( rc!=SQLITE_OK || memcmp(aMagic, aJournalMagic, 8) ) return rc;
+rc = sqlite3OsSeek(pJrnl, szJ-16-len);
+if( rc!=SQLITE_OK ) return rc;
+*pzMaster = (char *)sqliteMalloc(len+1);
+if( !*pzMaster ){
+return SQLITE_NOMEM;
+}
+rc = sqlite3OsRead(pJrnl, *pzMaster, len);
+if( rc!=SQLITE_OK ){
+sqliteFree(*pzMaster);
+*pzMaster = 0;
+return rc;
+}
+/* See if the checksum matches the master journal name */
+for(i=0; i<len; i++){
+cksum -= (*pzMaster)[i];
+}
+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.
+*/
+sqliteFree(*pzMaster);
+*pzMaster = 0;
+}else{
+(*pzMaster)[len] = '\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 int 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;
+return sqlite3OsSeek(pPager->jfd, pPager->journalOff);
+}
+/*
+** 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.
+**
+** Followed by (JOURNAL_HDR_SZ - 24) bytes of unused space.
+*/
+static int writeJournalHdr(Pager *pPager){
+char zHeader[sizeof(aJournalMagic)+16];
+int rc = seekJournalHdr(pPager);
+if( rc ) return rc;
+pPager->journalHdr = pPager->journalOff;
+if( pPager->stmtHdrOff==0 ){
+pPager->stmtHdrOff = pPager->journalHdr;
+}
+pPager->journalOff += JOURNAL_HDR_SZ(pPager);
+/* FIX ME:
+**
+** Possibly for a pager not in no-sync mode, the journal magic should not
+** be written until nRec is filled in as part of next syncJournal().
+**
+** Actually maybe the whole journal header should be delayed until that
+** point. Think about this.
+*/
+memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
+/* The nRec Field. 0xFFFFFFFF for no-sync journals. */
+put32bits(&zHeader[sizeof(aJournalMagic)], pPager->noSync ? 0xffffffff : 0);
+/* The random check-hash initialiser */
+sqlite3Randomness(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);
+rc = sqlite3OsWrite(pPager->jfd, zHeader, sizeof(zHeader));
+/* The journal header has been written successfully. Seek the journal
+** file descriptor to the end of the journal header sector.
+*/
+if( rc==SQLITE_OK ){
+rc = sqlite3OsSeek(pPager->jfd, pPager->journalOff-1);
+if( rc==SQLITE_OK ){
+rc = sqlite3OsWrite(pPager->jfd, "\000", 1);
+}
+}
+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 */
+rc = seekJournalHdr(pPager);
+if( rc ) return rc;
+if( pPager->journalOff+JOURNAL_HDR_SZ(pPager) > journalSize ){
+return SQLITE_DONE;
+}
+rc = sqlite3OsRead(pPager->jfd, aMagic, sizeof(aMagic));
+if( rc ) return rc;
+if( memcmp(aMagic, aJournalMagic, sizeof(aMagic))!=0 ){
+return SQLITE_DONE;
+}
+rc = read32bits(pPager->jfd, pNRec);
+if( rc ) return rc;
+rc = read32bits(pPager->jfd, &pPager->cksumInit);
+if( rc ) return rc;
+rc = read32bits(pPager->jfd, pDbSize);
+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, (u32 *)&pPager->sectorSize);
+if( rc ) return rc;
+pPager->journalOff += JOURNAL_HDR_SZ(pPager);
+rc = sqlite3OsSeek(pPager->jfd, pPager->journalOff);
+return rc;
+}
+/*
+** Write the supplied master journal name into the journal file for pager
+** pPager at the current location. The master journal name must be the last
+** thing written to a journal file. If the pager is in full-sync mode, the
+** journal file descriptor is advanced to the next sector boundary before
+** anything is written. The format is:
+**
+** + 4 bytes: PAGER_MJ_PGNO.
+** + N bytes: 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;
+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 ){
+rc = seekJournalHdr(pPager);
+if( rc!=SQLITE_OK ) return rc;
+}
+pPager->journalOff += (len+20);
+rc = write32bits(pPager->jfd, PAGER_MJ_PGNO(pPager));
+if( rc!=SQLITE_OK ) return rc;
+rc = sqlite3OsWrite(pPager->jfd, zMaster, len);
+if( rc!=SQLITE_OK ) return rc;
+put32bits(zBuf, len);
+put32bits(&zBuf[4], cksum);
+memcpy(&zBuf[8], aJournalMagic, sizeof(aJournalMagic));
+rc = sqlite3OsWrite(pPager->jfd, zBuf, 8+sizeof(aJournalMagic));
+pPager->needSync = !pPager->noSync;
+return rc;
+}
+/*
+** Add or remove a page from the list of all pages that are in the
+** statement journal.
+**
+** The Pager keeps a separate list of pages that are currently in
+** the statement journal.  This helps the sqlite3pager_stmt_commit()
+** routine run MUCH faster for the common case where there are many
+** pages in memory but only a few are in the statement journal.
+*/
+static void page_add_to_stmt_list(PgHdr *pPg){
+Pager *pPager = pPg->pPager;
+if( pPg->inStmt ) return;
+assert( pPg->pPrevStmt==0 && pPg->pNextStmt==0 );
+pPg->pPrevStmt = 0;
+if( pPager->pStmt ){
+pPager->pStmt->pPrevStmt = pPg;
+}
+pPg->pNextStmt = pPager->pStmt;
+pPager->pStmt = pPg;
+pPg->inStmt = 1;
+}
+static void page_remove_from_stmt_list(PgHdr *pPg){
+if( !pPg->inStmt ) return;
+if( pPg->pPrevStmt ){
+assert( pPg->pPrevStmt->pNextStmt==pPg );
+pPg->pPrevStmt->pNextStmt = pPg->pNextStmt;
+}else{
+assert( pPg->pPager->pStmt==pPg );
+pPg->pPager->pStmt = pPg->pNextStmt;
+}
+if( pPg->pNextStmt ){
+assert( pPg->pNextStmt->pPrevStmt==pPg );
+pPg->pNextStmt->pPrevStmt = pPg->pPrevStmt;
+}
+pPg->pNextStmt = 0;
+pPg->pPrevStmt = 0;
+pPg->inStmt = 0;
+}
+/*
+** 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;
+if( pPager->aHash==0 ) return 0;
+p = pPager->aHash[pgno & (pPager->nHash-1)];
+while( p && p->pgno!=pgno ){
+p = p->pNextHash;
+}
+return p;
+}
+/*
+** Unlock the database and 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){
+PgHdr *pPg, *pNext;
+if( pPager->errCode ) return;
+for(pPg=pPager->pAll; pPg; pPg=pNext){
+pNext = pPg->pNextAll;
+sqliteFree(pPg);
+}
+pPager->pFirst = 0;
+pPager->pFirstSynced = 0;
+pPager->pLast = 0;
+pPager->pAll = 0;
+pPager->nHash = 0;
+sqliteFree(pPager->aHash);
+pPager->nPage = 0;
+pPager->aHash = 0;
+if( pPager->state>=PAGER_RESERVED ){
+sqlite3pager_rollback(pPager);
+}
+sqlite3OsUnlock(pPager->fd, NO_LOCK);
+pPager->state = PAGER_UNLOCK;
+pPager->dbSize = -1;
+pPager->nRef = 0;
+assert( pPager->journalOpen==0 );
+}
+/*
+** When this routine is called, the pager has the journal file open and
+** a RESERVED or EXCLUSIVE lock on the database.  This routine releases
+** the database lock and acquires a SHARED lock in its place.  The journal
+** file is deleted and closed.
+**
+** 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_unwritelock(Pager *pPager){
+PgHdr *pPg;
+int rc;
+assert( !MEMDB );
+if( pPager->state<PAGER_RESERVED ){
+return SQLITE_OK;
+}
+sqlite3pager_stmt_commit(pPager);
+if( pPager->stmtOpen ){
+sqlite3OsClose(&pPager->stfd);
+pPager->stmtOpen = 0;
+}
+if( pPager->journalOpen ){
+sqlite3OsClose(&pPager->jfd);
+pPager->journalOpen = 0;
+sqlite3OsDelete(pPager->zJournal);
+sqliteFree( pPager->aInJournal );
+pPager->aInJournal = 0;
+for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
+pPg->inJournal = 0;
+pPg->dirty = 0;
+pPg->needSync = 0;
+#ifdef SQLITE_CHECK_PAGES
+pPg->pageHash = pager_pagehash(pPg);
+#endif
+}
+pPager->pDirty = 0;
+pPager->dirtyCache = 0;
+pPager->nRec = 0;
+}else{
+assert( pPager->aInJournal==0 );
+assert( pPager->dirtyCache==0 || pPager->useJournal==0 );
+}
+rc = sqlite3OsUnlock(pPager->fd, SHARED_LOCK);
+pPager->state = PAGER_SHARED;
+pPager->origDbSize = 0;
+pPager->setMaster = 0;
+pPager->needSync = 0;
+pPager->pFirstSynced = pPager->pFirst;
+return 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.
+**
+** If useCksum==0 it means this journal does not use checksums.  Checksums
+** are not used in statement journals because statement journals do not
+** need to survive power failures.
+*/
+static int pager_playback_one_page(Pager *pPager, OsFile *jfd, int useCksum){
+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[SQLITE_MAX_PAGE_SIZE];  /* Temp storage for a page */
+/* useCksum should be true for the main journal and false for
+** statement journals.  Verify that this is always the case
+*/
+assert( jfd == (useCksum ? pPager->jfd : pPager->stfd) );
+rc = read32bits(jfd, &pgno);
+if( rc!=SQLITE_OK ) return rc;
+rc = sqlite3OsRead(jfd, &aData, pPager->pageSize);
+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( useCksum ){
+rc = read32bits(jfd, &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.
+**
+** 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 in the main rollback
+** journal.  Otherwise, if a full ROLLBACK occurs after the statement
+** rollback the full ROLLBACK will not restore the page to its original
+** content.  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 in the main journal either because the page is not in
+** cache or else it is marked as needSync==0.
+*/
+pPg = pager_lookup(pPager, pgno);
+assert( pPager->state>=PAGER_EXCLUSIVE || pPg!=0 );
+TRACE3("PLAYBACK %d page %d\n", PAGERID(pPager), pgno);
+if( pPager->state>=PAGER_EXCLUSIVE && (pPg==0 || pPg->needSync==0) ){
+rc = sqlite3OsSeek(pPager->fd, (pgno-1)*(i64)pPager->pageSize);
+if( rc==SQLITE_OK ){
+rc = sqlite3OsWrite(pPager->fd, aData, pPager->pageSize);
+}
+if( pPg ){
+makeClean(pPg);
+}
+}
+if( pPg ){
+/* No page should ever be explicitly rolled back that is in use, except
+** for page 1 which is held in use in order to keep the lock on the
+** database active. However such a page may be rolled back as a result
+** of an internal error resulting in an automatic call to
+** sqlite3pager_rollback().
+*/
+void *pData;
+/* assert( pPg->nRef==0 || pPg->pgno==1 ); */
+pData = PGHDR_TO_DATA(pPg);
+memcpy(pData, aData, pPager->pageSize);
+if( pPager->xDestructor ){  /*** FIX ME:  Should this be xReinit? ***/
+pPager->xDestructor(pData, pPager->pageSize);
+}
+#ifdef SQLITE_CHECK_PAGES
+pPg->pageHash = pager_pagehash(pPg);
+#endif
+CODEC1(pPager, pData, pPg->pgno, 3);
+}
+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.
+**
+** 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(const char *zMaster){
+int rc;
+int master_open = 0;
+OsFile *master = 0;
+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.
+*/
+rc = sqlite3OsOpenReadOnly(zMaster, &master);
+if( rc!=SQLITE_OK ) goto delmaster_out;
+master_open = 1;
+rc = sqlite3OsFileSize(master, &nMasterJournal);
+if( rc!=SQLITE_OK ) goto delmaster_out;
+if( nMasterJournal>0 ){
+char *zJournal;
+char *zMasterPtr = 0;
+/* Load the entire master journal file into space obtained from
+** sqliteMalloc() and pointed to by zMasterJournal.
+*/
+zMasterJournal = (char *)sqliteMalloc(nMasterJournal);
+if( !zMasterJournal ){
+rc = SQLITE_NOMEM;
+goto delmaster_out;
+}
+rc = sqlite3OsRead(master, zMasterJournal, nMasterJournal);
+if( rc!=SQLITE_OK ) goto delmaster_out;
+zJournal = zMasterJournal;
+while( (zJournal-zMasterJournal)<nMasterJournal ){
+if( sqlite3OsFileExists(zJournal) ){
+/* 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.
+*/
+OsFile *journal = 0;
+int c;
+rc = sqlite3OsOpenReadOnly(zJournal, &journal);
+if( rc!=SQLITE_OK ){
+goto delmaster_out;
+}
+rc = readMasterJournal(journal, &zMasterPtr);
+sqlite3OsClose(&journal);
+if( rc!=SQLITE_OK ){
+goto delmaster_out;
+}
+c = zMasterPtr!=0 && strcmp(zMasterPtr, zMaster)==0;
+sqliteFree(zMasterPtr);
+if( c ){
+/* We have a match. Do not delete the master journal file. */
+goto delmaster_out;
+}
+}
+zJournal += (strlen(zJournal)+1);
+}
+}
+sqlite3OsDelete(zMaster);
+delmaster_out:
+if( zMasterJournal ){
+sqliteFree(zMasterJournal);
+}
+if( master_open ){
+sqlite3OsClose(&master);
+}
+return rc;
+}
+/*
+** Make every page in the cache agree with what is on disk.  In other words,
+** reread the disk to reset the state of the cache.
+**
+** This routine is called after a rollback in which some of the dirty cache
+** pages had never been written out to disk.  We need to roll back the
+** cache content and the easiest way to do that is to reread the old content
+** back from the disk.
+*/
+static int pager_reload_cache(Pager *pPager){
+PgHdr *pPg;
+int rc = SQLITE_OK;
+for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
+char zBuf[SQLITE_MAX_PAGE_SIZE];
+if( !pPg->dirty ) continue;
+if( (int)pPg->pgno <= pPager->origDbSize ){
+rc = sqlite3OsSeek(pPager->fd, pPager->pageSize*(i64)(pPg->pgno-1));
+if( rc==SQLITE_OK ){
+rc = sqlite3OsRead(pPager->fd, zBuf, pPager->pageSize);
+}
+TRACE3("REFETCH %d page %d\n", PAGERID(pPager), pPg->pgno);
+if( rc ) break;
+CODEC1(pPager, zBuf, pPg->pgno, 2);
+}else{
+memset(zBuf, 0, pPager->pageSize);
+}
+if( pPg->nRef==0 || memcmp(zBuf, PGHDR_TO_DATA(pPg), pPager->pageSize) ){
+memcpy(PGHDR_TO_DATA(pPg), zBuf, pPager->pageSize);
+if( pPager->xReiniter ){
+pPager->xReiniter(PGHDR_TO_DATA(pPg), pPager->pageSize);
+}else{
+memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
+}
+}
+pPg->needSync = 0;
+pPg->dirty = 0;
+#ifdef SQLITE_CHECK_PAGES
+pPg->pageHash = pager_pagehash(pPg);
+#endif
+}
+pPager->pDirty = 0;
+return rc;
+}
+/*
+** Truncate the main file of the given pager to the number of pages
+** indicated.
+*/
+static int pager_truncate(Pager *pPager, int nPage){
+assert( pPager->state>=PAGER_EXCLUSIVE );
+return sqlite3OsTruncate(pPager->fd, pPager->pageSize*(i64)nPage);
+}
+/*
+** 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 integer which is the number of bytes in the master journal
+**       name.  The value may be zero (indicate that there is no master
+**       journal.)
+**  (6)  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.
+**  (7)  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 6 items above.
+** Each entry in the journal is an instance of the 7th 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){
+i64 szJ;                 /* Size of the journal file in bytes */
+u32 nRec;                /* Number of Records in the journal */
+int i;                   /* Loop counter */
+Pgno mxPg = 0;           /* Size of the original file in pages */
+int rc;                  /* Result code of a subroutine */
+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 ){
+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.
+*/
+rc = readMasterJournal(pPager->jfd, &zMaster);
+assert( rc!=SQLITE_DONE );
+if( rc!=SQLITE_OK || (zMaster && !sqlite3OsFileExists(zMaster)) ){
+sqliteFree(zMaster);
+zMaster = 0;
+if( rc==SQLITE_DONE ) rc = SQLITE_OK;
+goto end_playback;
+}
+sqlite3OsSeek(pPager->jfd, 0);
+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 this is the first header read from the journal, truncate the
+** database file back to it's original size.
+*/
+if( pPager->state>=PAGER_EXCLUSIVE &&
+pPager->journalOff==JOURNAL_HDR_SZ(pPager) ){
+assert( pPager->origDbSize==0 || pPager->origDbSize==mxPg );
+rc = pager_truncate(pPager, mxPg);
+if( rc!=SQLITE_OK ){
+goto end_playback;
+}
+pPager->dbSize = mxPg;
+}
+/* Copy original pages out of the journal and back into the database file.
+*/
+for(i=0; i<nRec; i++){
+rc = pager_playback_one_page(pPager, pPager->jfd, 1);
+if( rc!=SQLITE_OK ){
+if( rc==SQLITE_DONE ){
+rc = SQLITE_OK;
+pPager->journalOff = szJ;
+break;
+}else{
+goto end_playback;
+}
+}
+}
+}
+/*NOTREACHED*/
+assert( 0 );
+end_playback:
+if( rc==SQLITE_OK ){
+rc = pager_unwritelock(pPager);
+}
+if( zMaster ){
+/* If there was a master journal and this routine will return true,
+** see if it is possible to delete the master journal.
+*/
+if( rc==SQLITE_OK ){
+rc = pager_delmaster(zMaster);
+}
+sqliteFree(zMaster);
+}
+/* The Pager.sectorSize variable may have been updated while rolling
+** back a journal created by a process with a different PAGER_SECTOR_SIZE
+** value. Reset it to the correct value for this process.
+*/
+pPager->sectorSize = PAGER_SECTOR_SIZE;
+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;
+#ifndef NDEBUG
+{
+i64 os_szJ;
+rc = sqlite3OsFileSize(pPager->jfd, &os_szJ);
+if( rc!=SQLITE_OK ) return rc;
+assert( szJ==os_szJ );
+}
+#endif
+/* Set hdrOff to be the offset to the first journal header written
+** this statement transaction, 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.
+*/
+if( pPager->state>=PAGER_EXCLUSIVE ){
+rc = pager_truncate(pPager, pPager->stmtSize);
+}
+pPager->dbSize = pPager->stmtSize;
+/* Figure out how many records are in the statement journal.
+*/
+assert( pPager->stmtInUse && pPager->journalOpen );
+sqlite3OsSeek(pPager->stfd, 0);
+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=nRec-1; i>=0; i--){
+rc = pager_playback_one_page(pPager, pPager->stfd, 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.
+*/
+rc = sqlite3OsSeek(pPager->jfd, pPager->stmtJSize);
+if( rc!=SQLITE_OK ){
+goto end_stmt_playback;
+}
+pPager->journalOff = pPager->stmtJSize;
+pPager->cksumInit = pPager->stmtCksum;
+assert( JOURNAL_HDR_SZ(pPager)<(pPager->pageSize+8) );
+while( pPager->journalOff <= (hdrOff-(pPager->pageSize+8)) ){
+rc = pager_playback_one_page(pPager, pPager->jfd, 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, 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 sqlite3pager_set_cachesize(Pager *pPager, int mxPage){
+if( mxPage>10 ){
+pPager->mxPage = mxPage;
+}else{
+pPager->mxPage = 10;
+}
+}
+/*
+** 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 sqlite3pager_set_safety_level(Pager *pPager, int level, int full_fsync){
+pPager->noSync =  level==1 || pPager->tempFile;
+pPager->fullSync = level==3 && !pPager->tempFile;
+pPager->full_fsync = full_fsync;
+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 name of the file into zFile
+** (zFile must be at least SQLITE_TEMPNAME_SIZE bytes long.)  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 sqlite3pager_opentemp(char *zFile, OsFile **pFd){
+int cnt = 8;
+int rc;
+#ifdef SQLITE_TEST
+sqlite3_opentemp_count++;  /* Used for testing and analysis only */
+#endif
+do{
+cnt--;
+sqlite3OsTempFileName(zFile);
+rc = sqlite3OsOpenExclusive(zFile, pFd, 1);
+}while( cnt>0 && rc!=SQLITE_OK && rc!=SQLITE_NOMEM );
+return rc;
+}
+/*
+** 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 sqlite3pager_get() and is only held open until the
+** last page is released using sqlite3pager_unref().
+**
+** 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 sqlite3pager_open(
+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 */
+){
+Pager *pPager = 0;
+char *zFullPathname = 0;
+int nameLen;  /* Compiler is wrong. This is always initialized before use */
+OsFile *fd;
+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;
+char zTemp[SQLITE_TEMPNAME_SIZE];
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+/* A malloc() cannot fail in sqlite3ThreadData() as one or more calls to
+** malloc() must have already been made by this thread before it gets
+** to this point. This means the ThreadData must have been allocated already
+** so that ThreadData.nAlloc can be set. It would be nice to assert
+** that ThreadData.nAlloc is non-zero, but alas this breaks test cases
+** written to invoke the pager directly.
+*/
+ThreadData *pTsd = sqlite3ThreadData();
+assert( pTsd );
+#endif
+/* If malloc() has already failed return SQLITE_NOMEM. Before even
+** testing for this, set *ppPager to NULL so the caller knows the pager
+** structure was never allocated.
+*/
+*ppPager = 0;
+if( sqlite3MallocFailed() ){
+return SQLITE_NOMEM;
+}
+memset(&fd, 0, sizeof(fd));
+/* Open the pager file and set zFullPathname to point at malloc()ed
+** memory containing the complete filename (i.e. including the directory).
+*/
+if( zFilename && zFilename[0] ){
+#ifndef SQLITE_OMIT_MEMORYDB
+if( strcmp(zFilename,":memory:")==0 ){
+memDb = 1;
+zFullPathname = sqliteStrDup("");
+}else
+#endif
+{
+zFullPathname = sqlite3OsFullPathname(zFilename);
+if( zFullPathname ){
+rc = sqlite3OsOpenReadWrite(zFullPathname, &fd, &readOnly);
+}
+}
+}else{
+rc = sqlite3pager_opentemp(zTemp, &fd);
+zFilename = zTemp;
+zFullPathname = sqlite3OsFullPathname(zFilename);
+if( rc==SQLITE_OK ){
+tempFile = 1;
+}
+}
+/* Allocate the Pager structure. As part of the same allocation, allocate
+** space for the full paths of the file, directory and journal
+** (Pager.zFilename, Pager.zDirectory and Pager.zJournal).
+*/
+if( zFullPathname ){
+nameLen = strlen(zFullPathname);
+pPager = sqliteMalloc( sizeof(*pPager) + nameLen*3 + 30 );
+}
+/* If an error occured in either of the blocks above, free the memory
+** pointed to by zFullPathname, 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 || !zFullPathname || rc!=SQLITE_OK ){
+sqlite3OsClose(&fd);
+sqliteFree(zFullPathname);
+sqliteFree(pPager);
+return ((rc==SQLITE_OK)?SQLITE_NOMEM:rc);
+}
+TRACE3("OPEN %d %s\n", FILEHANDLEID(fd), zFullPathname);
+pPager->zFilename = (char*)&pPager[1];
+pPager->zDirectory = &pPager->zFilename[nameLen+1];
+pPager->zJournal = &pPager->zDirectory[nameLen+1];
+strcpy(pPager->zFilename, zFullPathname);
+strcpy(pPager->zDirectory, zFullPathname);
+for(i=nameLen; i>0 && pPager->zDirectory[i-1]!='/'; i--){}
+if( i>0 ) pPager->zDirectory[i-1] = 0;
+strcpy(pPager->zJournal, zFullPathname);
+sqliteFree(zFullPathname);
+strcpy(&pPager->zJournal[nameLen], "-journal");
+pPager->fd = fd;
+/* pPager->journalOpen = 0; */
+pPager->useJournal = useJournal && !memDb;
+pPager->noReadlock = noReadlock && readOnly;
+/* pPager->stmtOpen = 0; */
+/* pPager->stmtInUse = 0; */
+/* pPager->nRef = 0; */
+pPager->dbSize = memDb-1;
+pPager->pageSize = SQLITE_DEFAULT_PAGE_SIZE;
+/* pPager->stmtSize = 0; */
+/* pPager->stmtJSize = 0; */
+/* pPager->nPage = 0; */
+/* pPager->nMaxPage = 0; */
+pPager->mxPage = 100;
+assert( PAGER_UNLOCK==0 );
+/* pPager->state = PAGER_UNLOCK; */
+/* pPager->errMask = 0; */
+pPager->tempFile = tempFile;
+pPager->memDb = memDb;
+pPager->readOnly = readOnly;
+/* pPager->needSync = 0; */
+pPager->noSync = pPager->tempFile || !useJournal;
+pPager->fullSync = (pPager->noSync?0:1);
+/* pPager->pFirst = 0; */
+/* pPager->pFirstSynced = 0; */
+/* pPager->pLast = 0; */
+pPager->nExtra = FORCE_ALIGNMENT(nExtra);
+pPager->sectorSize = PAGER_SECTOR_SIZE;
+/* pPager->pBusyHandler = 0; */
+/* memset(pPager->aHash, 0, sizeof(pPager->aHash)); */
+*ppPager = pPager;
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+pPager->pNext = pTsd->pPager;
+pTsd->pPager = pPager;
+#endif
+return SQLITE_OK;
+}
+/*
+** Set the busy handler function.
+*/
+void sqlite3pager_set_busyhandler(Pager *pPager, BusyHandler *pBusyHandler){
+pPager->pBusyHandler = pBusyHandler;
+}
+/*
+** Set the destructor for this pager.  If not NULL, the destructor is called
+** when the reference count on each page reaches zero.  The destructor can
+** be used to clean up information in the extra segment appended to each page.
+**
+** The destructor is not called as a result sqlite3pager_close().
+** Destructors are only called by sqlite3pager_unref().
+*/
+void sqlite3pager_set_destructor(Pager *pPager, void (*xDesc)(void*,int)){
+pPager->xDestructor = xDesc;
+}
+/*
+** 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 sqlite3pager_set_reiniter(Pager *pPager, void (*xReinit)(void*,int)){
+pPager->xReiniter = xReinit;
+}
+/*
+** Set the page size.  Return the new size.  If the suggest new page
+** size is inappropriate, then an alternative page size is selected
+** and returned.
+*/
+int sqlite3pager_set_pagesize(Pager *pPager, int pageSize){
+assert( pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE );
+if( !pPager->memDb ){
+pPager->pageSize = pageSize;
+}
+return pPager->pageSize;
+}
+/*
+** 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 clear_simulated_io_error(){
+sqlite3_io_error_hit = 0;
+}
+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 clear_simulated_io_error()
+# 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).
+*/
+void sqlite3pager_read_fileheader(Pager *pPager, int N, unsigned char *pDest){
+memset(pDest, 0, N);
+if( MEMDB==0 ){
+disable_simulated_io_errors();
+sqlite3OsSeek(pPager->fd, 0);
+sqlite3OsRead(pPager->fd, pDest, N);
+enable_simulated_io_errors();
+}
+}
+/*
+** 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 sqlite3pager_pagecount(Pager *pPager){
+i64 n;
+assert( pPager!=0 );
+if( pPager->dbSize>=0 ){
+n = pPager->dbSize;
+} else {
+if( sqlite3OsFileSize(pPager->fd, &n)!=SQLITE_OK ){
+pager_error(pPager, SQLITE_IOERR);
+return 0;
+}
+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++;
+}
+return n;
+}
+#ifndef SQLITE_OMIT_MEMORYDB
+/*
+** Clear a PgHistory block
+*/
+static void clearHistory(PgHistory *pHist){
+sqliteFree(pHist->pOrig);
+sqliteFree(pHist->pStmt);
+pHist->pOrig = 0;
+pHist->pStmt = 0;
+}
+#else
+#define clearHistory(x)
+#endif
+/*
+** Forward declaration
+*/
+static int syncJournal(Pager*);
+/*
+** Unlink pPg from it's hash chain. Also set the page number to 0 to indicate
+** that the page is not part of any hash chain. This is required because the
+** sqlite3pager_movepage() routine can leave a page in the
+** pNextFree/pPrevFree list that is not a part of any hash-chain.
+*/
+static void unlinkHashChain(Pager *pPager, PgHdr *pPg){
+if( pPg->pgno==0 ){
+assert( pPg->pNextHash==0 && pPg->pPrevHash==0 );
+return;
+}
+if( pPg->pNextHash ){
+pPg->pNextHash->pPrevHash = pPg->pPrevHash;
+}
+if( pPg->pPrevHash ){
+assert( pPager->aHash[pPg->pgno & (pPager->nHash-1)]!=pPg );
+pPg->pPrevHash->pNextHash = pPg->pNextHash;
+}else{
+int h = pPg->pgno & (pPager->nHash-1);
+pPager->aHash[h] = pPg->pNextHash;
+}
+if( MEMDB ){
+clearHistory(PGHDR_TO_HIST(pPg, pPager));
+}
+pPg->pgno = 0;
+pPg->pNextHash = pPg->pPrevHash = 0;
+}
+/*
+** Unlink a page from the free list (the list of all pages where nRef==0)
+** and from its hash collision chain.
+*/
+static void unlinkPage(PgHdr *pPg){
+Pager *pPager = pPg->pPager;
+/* Keep the pFirstSynced pointer pointing at the first synchronized page */
+if( pPg==pPager->pFirstSynced ){
+PgHdr *p = pPg->pNextFree;
+while( p && p->needSync ){ p = p->pNextFree; }
+pPager->pFirstSynced = p;
+}
+/* Unlink from the freelist */
+if( pPg->pPrevFree ){
+pPg->pPrevFree->pNextFree = pPg->pNextFree;
+}else{
+assert( pPager->pFirst==pPg );
+pPager->pFirst = pPg->pNextFree;
+}
+if( pPg->pNextFree ){
+pPg->pNextFree->pPrevFree = pPg->pPrevFree;
+}else{
+assert( pPager->pLast==pPg );
+pPager->pLast = pPg->pPrevFree;
+}
+pPg->pNextFree = pPg->pPrevFree = 0;
+/* Unlink from the pgno hash table */
+unlinkHashChain(pPager, pPg);
+}
+#ifndef SQLITE_OMIT_MEMORYDB
+/*
+** This routine is used to truncate an in-memory database.  Delete
+** all pages whose pgno is larger than pPager->dbSize and is unreferenced.
+** Referenced pages larger than pPager->dbSize are zeroed.
+*/
+static void memoryTruncate(Pager *pPager){
+PgHdr *pPg;
+PgHdr **ppPg;
+int dbSize = pPager->dbSize;
+ppPg = &pPager->pAll;
+while( (pPg = *ppPg)!=0 ){
+if( pPg->pgno<=dbSize ){
+ppPg = &pPg->pNextAll;
+}else if( pPg->nRef>0 ){
+memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
+ppPg = &pPg->pNextAll;
+}else{
+*ppPg = pPg->pNextAll;
+unlinkPage(pPg);
+makeClean(pPg);
+sqliteFree(pPg);
+pPager->nPage--;
+}
+}
+}
+#else
+#define memoryTruncate(p)
+#endif
+/*
+** 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;
+assert( PAGER_SHARED==SHARED_LOCK );
+assert( PAGER_RESERVED==RESERVED_LOCK );
+assert( PAGER_EXCLUSIVE==EXCLUSIVE_LOCK );
+if( pPager->state>=locktype ){
+rc = SQLITE_OK;
+}else{
+do {
+rc = sqlite3OsLock(pPager->fd, locktype);
+}while( rc==SQLITE_BUSY && sqlite3InvokeBusyHandler(pPager->pBusyHandler) );
+if( rc==SQLITE_OK ){
+pPager->state = locktype;
+}
+}
+return rc;
+}
+/*
+** Truncate the file to the number of pages specified.
+*/
+int sqlite3pager_truncate(Pager *pPager, Pgno nPage){
+int rc;
+sqlite3pager_pagecount(pPager);
+if( pPager->errCode ){
+rc = pPager->errCode;
+return rc;
+}
+if( nPage>=(unsigned)pPager->dbSize ){
+return SQLITE_OK;
+}
+if( MEMDB ){
+pPager->dbSize = nPage;
+memoryTruncate(pPager);
+return SQLITE_OK;
+}
+rc = syncJournal(pPager);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+/* Get an exclusive lock on the database before truncating. */
+rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+rc = pager_truncate(pPager, nPage);
+if( rc==SQLITE_OK ){
+pPager->dbSize = 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 sqlite3pager_close(Pager *pPager){
+PgHdr *pPg, *pNext;
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+/* A malloc() cannot fail in sqlite3ThreadData() as one or more calls to
+** malloc() must have already been made by this thread before it gets
+** to this point. This means the ThreadData must have been allocated already
+** so that ThreadData.nAlloc can be set.
+*/
+ThreadData *pTsd = sqlite3ThreadData();
+assert( pPager );
+assert( pTsd && pTsd->nAlloc );
+#endif
+switch( pPager->state ){
+case PAGER_RESERVED:
+case PAGER_SYNCED:
+case PAGER_EXCLUSIVE: {
+/* We ignore any IO errors that occur during the rollback
+** operation. So disable IO error simulation so that testing
+** works more easily.
+*/
+disable_simulated_io_errors();
+sqlite3pager_rollback(pPager);
+enable_simulated_io_errors();
+if( !MEMDB ){
+sqlite3OsUnlock(pPager->fd, NO_LOCK);
+}
+assert( pPager->errCode || pPager->journalOpen==0 );
+break;
+}
+case PAGER_SHARED: {
+if( !MEMDB ){
+sqlite3OsUnlock(pPager->fd, NO_LOCK);
+}
+break;
+}
+default: {
+/* Do nothing */
+break;
+}
+}
+for(pPg=pPager->pAll; pPg; pPg=pNext){
+#ifndef NDEBUG
+if( MEMDB ){
+PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+assert( !pPg->alwaysRollback );
+assert( !pHist->pOrig );
+assert( !pHist->pStmt );
+}
+#endif
+pNext = pPg->pNextAll;
+sqliteFree(pPg);
+}
+TRACE2("CLOSE %d\n", PAGERID(pPager));
+assert( pPager->errCode || (pPager->journalOpen==0 && pPager->stmtOpen==0) );
+if( pPager->journalOpen ){
+sqlite3OsClose(&pPager->jfd);
+}
+sqliteFree(pPager->aInJournal);
+if( pPager->stmtOpen ){
+sqlite3OsClose(&pPager->stfd);
+}
+sqlite3OsClose(&pPager->fd);
+/* Temp files are automatically deleted by the OS
+** if( pPager->tempFile ){
+**   sqlite3OsDelete(pPager->zFilename);
+** }
+*/
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+/* Remove the pager from the linked list of pagers starting at
+** ThreadData.pPager if memory-management is enabled.
+*/
+if( pPager==pTsd->pPager ){
+pTsd->pPager = pPager->pNext;
+}else{
+Pager *pTmp;
+for(pTmp = pTsd->pPager; pTmp->pNext!=pPager; pTmp=pTmp->pNext){}
+pTmp->pNext = pPager->pNext;
+}
+#endif
+sqliteFree(pPager->aHash);
+sqliteFree(pPager);
+return SQLITE_OK;
+}
+/*
+** Return the page number for the given page data.
+*/
+Pgno sqlite3pager_pagenumber(void *pData){
+PgHdr *p = DATA_TO_PGHDR(pData);
+return p->pgno;
+}
+/*
+** The page_ref() function increments the reference count for a page.
+** If the page is currently on the freelist (the reference count is zero) then
+** remove it from the freelist.
+**
+** For non-test systems, page_ref() is a macro that calls _page_ref()
+** online of the reference count is zero.  For test systems, page_ref()
+** is a real function so that we can set breakpoints and trace it.
+*/
+static void _page_ref(PgHdr *pPg){
+if( pPg->nRef==0 ){
+/* The page is currently on the freelist.  Remove it. */
+if( pPg==pPg->pPager->pFirstSynced ){
+PgHdr *p = pPg->pNextFree;
+while( p && p->needSync ){ p = p->pNextFree; }
+pPg->pPager->pFirstSynced = p;
+}
+if( pPg->pPrevFree ){
+pPg->pPrevFree->pNextFree = pPg->pNextFree;
+}else{
+pPg->pPager->pFirst = pPg->pNextFree;
+}
+if( pPg->pNextFree ){
+pPg->pNextFree->pPrevFree = pPg->pPrevFree;
+}else{
+pPg->pPager->pLast = pPg->pPrevFree;
+}
+pPg->pPager->nRef++;
+}
+pPg->nRef++;
+REFINFO(pPg);
+}
+#ifdef SQLITE_DEBUG
+static void page_ref(PgHdr *pPg){
+if( pPg->nRef==0 ){
+_page_ref(pPg);
+}else{
+pPg->nRef++;
+REFINFO(pPg);
+}
+}
+#else
+# define page_ref(P)   ((P)->nRef==0?_page_ref(P):(void)(P)->nRef++)
+#endif
+/*
+** Increment the reference count for a page.  The input pointer is
+** a reference to the page data.
+*/
+int sqlite3pager_ref(void *pData){
+PgHdr *pPg = DATA_TO_PGHDR(pData);
+page_ref(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 sync occurs.
+**
+** This routine clears the needSync field of every page current held in
+** memory.
+*/
+static int syncJournal(Pager *pPager){
+PgHdr *pPg;
+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 ){
+assert( pPager->journalOpen );
+/* assert( !pPager->noSync ); // noSync might be set if synchronous
+** was turned off after the transaction was started.  Ticket #615 */
+#ifndef NDEBUG
+{
+/* Make sure the pPager->nRec counter we are keeping agrees
+** with the nRec computed from the size of the journal file.
+*/
+i64 jSz;
+rc = sqlite3OsFileSize(pPager->jfd, &jSz);
+if( rc!=0 ) return rc;
+assert( pPager->journalOff==jSz );
+}
+#endif
+{
+/* 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.
+*/
+if( pPager->fullSync ){
+TRACE2("SYNC journal of %d\n", PAGERID(pPager));
+rc = sqlite3OsSync(pPager->jfd, 0);
+if( rc!=0 ) return rc;
+}
+rc = sqlite3OsSeek(pPager->jfd,
+pPager->journalHdr + sizeof(aJournalMagic));
+if( rc ) return rc;
+rc = write32bits(pPager->jfd, pPager->nRec);
+if( rc ) return rc;
+rc = sqlite3OsSeek(pPager->jfd, pPager->journalOff);
+if( rc ) return rc;
+}
+TRACE2("SYNC journal of %d\n", PAGERID(pPager));
+rc = sqlite3OsSync(pPager->jfd, pPager->full_fsync);
+if( rc!=0 ) return rc;
+pPager->journalStarted = 1;
+}
+pPager->needSync = 0;
+/* Erase the needSync flag from every page.
+*/
+for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
+pPg->needSync = 0;
+}
+pPager->pFirstSynced = pPager->pFirst;
+}
+#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{
+for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
+assert( pPg->needSync==0 );
+}
+assert( pPager->pFirstSynced==pPager->pFirst );
+}
+#endif
+return rc;
+}
+/*
+** Merge two lists of pages connected by pDirty and in pgno order.
+** Do not both fixing the pPrevDirty pointers.
+*/
+static PgHdr *merge_pagelist(PgHdr *pA, PgHdr *pB){
+PgHdr result, *pTail;
+pTail = &result;
+while( pA && pB ){
+if( pA->pgno<pB->pgno ){
+pTail->pDirty = pA;
+pTail = pA;
+pA = pA->pDirty;
+}else{
+pTail->pDirty = pB;
+pTail = pB;
+pB = pB->pDirty;
+}
+}
+if( pA ){
+pTail->pDirty = pA;
+}else if( pB ){
+pTail->pDirty = pB;
+}else{
+pTail->pDirty = 0;
+}
+return result.pDirty;
+}
+/*
+** Sort the list of pages in accending order by pgno.  Pages are
+** connected by pDirty pointers.  The pPrevDirty pointers are
+** corrupted by this sort.
+*/
+#define N_SORT_BUCKET 25
+static PgHdr *sort_pagelist(PgHdr *pIn){
+PgHdr *a[N_SORT_BUCKET], *p;
+int i;
+memset(a, 0, sizeof(a));
+while( pIn ){
+p = pIn;
+pIn = p->pDirty;
+p->pDirty = 0;
+for(i=0; i<N_SORT_BUCKET-1; i++){
+if( a[i]==0 ){
+a[i] = p;
+break;
+}else{
+p = merge_pagelist(a[i], p);
+a[i] = 0;
+}
+}
+if( i==N_SORT_BUCKET-1 ){
+a[i] = merge_pagelist(a[i], p);
+}
+}
+p = a[0];
+for(i=1; i<N_SORT_BUCKET; i++){
+p = merge_pagelist(p, a[i]);
+}
+return p;
+}
+/*
+** Given a list of pages (connected by the PgHdr.pDirty pointer) write
+** every one of those pages out to the database file and mark them all
+** 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;
+}
+pList = sort_pagelist(pList);
+while( pList ){
+assert( pList->dirty );
+rc = sqlite3OsSeek(pPager->fd, (pList->pgno-1)*(i64)pPager->pageSize);
+if( rc ) return rc;
+/* If there are dirty pages in the page cache with page numbers greater
+** than Pager.dbSize, this means sqlite3pager_truncate() 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 ){
+char *pData = CODEC2(pPager, PGHDR_TO_DATA(pList), pList->pgno, 6);
+TRACE3("STORE %d page %d\n", PAGERID(pPager), pList->pgno);
+rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize);
+TEST_INCR(pPager->nWrite);
+}
+#ifndef NDEBUG
+else{
+TRACE3("NOSTORE %d page %d\n", PAGERID(pPager), pList->pgno);
+}
+#endif
+if( rc ) return rc;
+pList->dirty = 0;
+#ifdef SQLITE_CHECK_PAGES
+pList->pageHash = pager_pagehash(pList);
+#endif
+pList = pList->pDirty;
+}
+return SQLITE_OK;
+}
+/*
+** Collect every dirty page into a dirty list and
+** return a pointer to the head of that list.  All pages are
+** collected even if they are still in use.
+*/
+static PgHdr *pager_get_all_dirty_pages(Pager *pPager){
+return pPager->pDirty;
+}
+/*
+** Return TRUE 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.
+*/
+static int hasHotJournal(Pager *pPager){
+if( !pPager->useJournal ) return 0;
+if( !sqlite3OsFileExists(pPager->zJournal) ) return 0;
+if( sqlite3OsCheckReservedLock(pPager->fd) ) return 0;
+if( sqlite3pager_pagecount(pPager)==0 ){
+sqlite3OsDelete(pPager->zJournal);
+return 0;
+}else{
+return 1;
+}
+}
+/*
+** Try to find a page in the cache that can be recycled.
+**
+** This routine may return SQLITE_IOERR, SQLITE_FULL or SQLITE_OK. It
+** does not set the pPager->errCode variable.
+*/
+static int pager_recycle(Pager *pPager, int syncOk, PgHdr **ppPg){
+PgHdr *pPg;
+*ppPg = 0;
+/* Find a page to recycle.  Try to locate a page that does not
+** require us to do an fsync() on the journal.
+*/
+pPg = pPager->pFirstSynced;
+/* If we could not find a page that does not require an fsync()
+** on the journal file then fsync the journal file.  This is a
+** very slow operation, so we work hard to avoid it.  But sometimes
+** it can't be helped.
+*/
+if( pPg==0 && pPager->pFirst && syncOk && !MEMDB){
+int rc = syncJournal(pPager);
+if( rc!=0 ){
+return rc;
+}
+if( pPager->fullSync ){
+/* If in full-sync mode, write a new journal header into the
+** journal file. This is done to avoid ever modifying a journal
+** header that is involved in the rollback of pages that have
+** already been written to the database (in case the header is
+** trashed when the nRec field is updated).
+*/
+pPager->nRec = 0;
+assert( pPager->journalOff > 0 );
+rc = writeJournalHdr(pPager);
+if( rc!=0 ){
+return rc;
+}
+}
+pPg = pPager->pFirst;
+}
+if( pPg==0 ){
+return SQLITE_OK;
+}
+assert( pPg->nRef==0 );
+/* Write the page to the database file if it is dirty.
+*/
+if( pPg->dirty ){
+int rc;
+assert( pPg->needSync==0 );
+makeClean(pPg);
+pPg->dirty = 1;
+pPg->pDirty = 0;
+rc = pager_write_pagelist( pPg );
+if( rc!=SQLITE_OK ){
+return rc;
+}
+}
+assert( pPg->dirty==0 );
+/* If the page we are recycling is marked as alwaysRollback, then
+** set the global alwaysRollback flag, thus disabling the
+** sqlite_dont_rollback() optimization for the rest of this transaction.
+** It is necessary to do this because the page marked alwaysRollback
+** might be reloaded at a later time but at that point we won't remember
+** that is was marked alwaysRollback.  This means that all pages must
+** be marked as alwaysRollback from here on out.
+*/
+if( pPg->alwaysRollback ){
+pPager->alwaysRollback = 1;
+}
+/* Unlink the old page from the free list and the hash table
+*/
+unlinkPage(pPg);
+TEST_INCR(pPager->nOvfl);
+*ppPg = pPg;
+return SQLITE_OK;
+}
+/*
+** This function is called to free superfluous dynamically allocated memory
+** held by the pager system. Memory in use by any SQLite pager allocated
+** by the current thread may be sqliteFree()ed.
+**
+** nReq is the number of bytes of memory required. Once this much has
+** been released, the function returns. A negative value for nReq means
+** free as much memory as possible. The return value is the total number
+** of bytes of memory released.
+*/
+#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
+int sqlite3pager_release_memory(int nReq){
+const ThreadData *pTsdro = sqlite3ThreadDataReadOnly();
+Pager *p;
+int nReleased = 0;
+int i;
+/* If the the global mutex is held, this subroutine becomes a
+** o-op; zero bytes of memory are freed.  This is because
+** some of the code invoked by this function may also
+** try to obtain the mutex, resulting in a deadlock.
+*/
+if( sqlite3OsInMutex(0) ){
+return 0;
+}
+/* Outermost loop runs for at most two iterations. First iteration we
+** try to find memory that can be released without calling fsync(). Second
+** iteration (which only runs if the first failed to free nReq bytes of
+** memory) is permitted to call fsync(). This is of course much more
+** expensive.
+*/
+for(i=0; i<=1; i++){
+/* Loop through all the SQLite pagers opened by the current thread. */
+for(p=pTsdro->pPager; p && (nReq<0 || nReleased<nReq); p=p->pNext){
+PgHdr *pPg;
+int rc;
+/* For each pager, try to free as many pages as possible (without
+** calling fsync() if this is the first iteration of the outermost
+** loop).
+*/
+while( SQLITE_OK==(rc = pager_recycle(p, i, &pPg)) && pPg) {
+/* We've found a page to free. At this point the page has been
+** removed from the page hash-table, free-list and synced-list
+** (pFirstSynced). It is still in the all pages (pAll) list.
+** Remove it from this list before freeing.
+**
+** Todo: Check the Pager.pStmt list to make sure this is Ok. It
+** probably is though.
+*/
+PgHdr *pTmp;
+assert( pPg );
+page_remove_from_stmt_list(pPg);
+if( pPg==p->pAll ){
+p->pAll = pPg->pNextAll;
+}else{
+for( pTmp=p->pAll; pTmp->pNextAll!=pPg; pTmp=pTmp->pNextAll ){}
+pTmp->pNextAll = pPg->pNextAll;
+}
+nReleased += sqliteAllocSize(pPg);
+sqliteFree(pPg);
+}
+if( rc!=SQLITE_OK ){
+/* An error occured whilst writing to the database file or
+** journal in pager_recycle(). The error is not returned to the
+** caller of this function. Instead, set the Pager.errCode variable.
+** The error will be returned to the user (or users, in the case
+** of a shared pager cache) of the pager for which the error occured.
+*/
+assert( rc==SQLITE_IOERR || rc==SQLITE_FULL );
+assert( p->state>=PAGER_RESERVED );
+pager_error(p, rc);
+}
+}
+}
+return nReleased;
+}
+#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */
+/*
+** 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.
+**
+** A _get 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 sqlite3pager_lookup().  Both this routine and _lookup() attempt
+** to find a page in the in-memory cache first.  If the page is not already
+** in memory, this routine goes to disk to read it in whereas _lookup()
+** just returns 0.  This routine acquires a read-lock the first time it
+** has to go to disk, and could also playback an old journal if necessary.
+** Since _lookup() never goes to disk, it never has to deal with locks
+** or journal files.
+*/
+int sqlite3pager_get(Pager *pPager, Pgno pgno, void **ppPage){
+PgHdr *pPg;
+int rc;
+/* 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( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
+return pPager->errCode;
+}
+/* If this is the first page accessed, then get a SHARED lock
+** on the database file.
+*/
+if( pPager->nRef==0 && !MEMDB ){
+if( !pPager->noReadlock ){
+rc = pager_wait_on_lock(pPager, SHARED_LOCK);
+if( rc!=SQLITE_OK ){
+return pager_error(pPager, rc);
+}
+}
+/* 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( hasHotJournal(pPager) ){
+/* 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 it's own EXCLUSIVE lock on the database file.
+*/
+rc = sqlite3OsLock(pPager->fd, EXCLUSIVE_LOCK);
+if( rc!=SQLITE_OK ){
+sqlite3OsUnlock(pPager->fd, NO_LOCK);
+pPager->state = PAGER_UNLOCK;
+return pager_error(pPager, rc);
+}
+pPager->state = PAGER_EXCLUSIVE;
+/* Open the journal for reading only.  Return SQLITE_BUSY if
+** we are unable to open the journal file.
+**
+** The journal file does not need to be locked itself.  The
+** journal file is never open unless the main database file holds
+** a write lock, so there is never any chance of two or more
+** processes opening the journal at the same time.
+*/
+rc = sqlite3OsOpenReadOnly(pPager->zJournal, &pPager->jfd);
+if( rc!=SQLITE_OK ){
+sqlite3OsUnlock(pPager->fd, NO_LOCK);
+pPager->state = PAGER_UNLOCK;
+return SQLITE_BUSY;
+}
+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);
+if( rc!=SQLITE_OK ){
+return pager_error(pPager, rc);
+}
+}
+pPg = 0;
+}else{
+/* Search for page in cache */
+pPg = pager_lookup(pPager, pgno);
+if( MEMDB && pPager->state==PAGER_UNLOCK ){
+pPager->state = PAGER_SHARED;
+}
+}
+if( pPg==0 ){
+/* The requested page is not in the page cache. */
+int h;
+TEST_INCR(pPager->nMiss);
+if( pPager->nPage<pPager->mxPage || pPager->pFirst==0 || MEMDB ){
+/* Create a new page */
+if( pPager->nPage>=pPager->nHash ){
+pager_resize_hash_table(pPager,
+pPager->nHash<256 ? 256 : pPager->nHash*2);
+if( pPager->nHash==0 ){
+return SQLITE_NOMEM;
+}
+}
+pPg = sqliteMallocRaw( sizeof(*pPg) + pPager->pageSize
++ sizeof(u32) + pPager->nExtra
++ MEMDB*sizeof(PgHistory) );
+if( pPg==0 ){
+return SQLITE_NOMEM;
+}
+memset(pPg, 0, sizeof(*pPg));
+if( MEMDB ){
+memset(PGHDR_TO_HIST(pPg, pPager), 0, sizeof(PgHistory));
+}
+pPg->pPager = pPager;
+pPg->pNextAll = pPager->pAll;
+pPager->pAll = pPg;
+pPager->nPage++;
+if( pPager->nPage>pPager->nMaxPage ){
+assert( pPager->nMaxPage==(pPager->nPage-1) );
+pPager->nMaxPage++;
+}
+}else{
+rc = pager_recycle(pPager, 1, &pPg);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+assert(pPg) ;
+}
+pPg->pgno = pgno;
+if( pPager->aInJournal && (int)pgno<=pPager->origDbSize ){
+sqlite3CheckMemory(pPager->aInJournal, pgno/8);
+assert( pPager->journalOpen );
+pPg->inJournal = (pPager->aInJournal[pgno/8] & (1<<(pgno&7)))!=0;
+pPg->needSync = 0;
+}else{
+pPg->inJournal = 0;
+pPg->needSync = 0;
+}
+if( pPager->aInStmt && (int)pgno<=pPager->stmtSize
+&& (pPager->aInStmt[pgno/8] & (1<<(pgno&7)))!=0 ){
+page_add_to_stmt_list(pPg);
+}else{
+page_remove_from_stmt_list(pPg);
+}
+makeClean(pPg);
+pPg->nRef = 1;
+REFINFO(pPg);
+pPager->nRef++;
+if( pPager->nExtra>0 ){
+memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
+}
+if( pPager->errCode ){
+sqlite3pager_unref(PGHDR_TO_DATA(pPg));
+rc = pPager->errCode;
+return rc;
+}
+/* Populate the page with data, either by reading from the database
+** file, or by setting the entire page to zero.
+*/
+if( sqlite3pager_pagecount(pPager)<(int)pgno || MEMDB ){
+memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
+}else{
+assert( MEMDB==0 );
+rc = sqlite3OsSeek(pPager->fd, (pgno-1)*(i64)pPager->pageSize);
+if( rc==SQLITE_OK ){
+rc = sqlite3OsRead(pPager->fd, PGHDR_TO_DATA(pPg),
+pPager->pageSize);
+}
+TRACE3("FETCH %d page %d\n", PAGERID(pPager), pPg->pgno);
+CODEC1(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
+if( rc!=SQLITE_OK ){
+i64 fileSize;
+int rc2 = sqlite3OsFileSize(pPager->fd, &fileSize);
+if( rc2!=SQLITE_OK || fileSize>=pgno*pPager->pageSize ){
+	  /* An IO error occured in one of the the sqlite3OsSeek() or
+** sqlite3OsRead() calls above. */
+pPg->pgno = 0;
+sqlite3pager_unref(PGHDR_TO_DATA(pPg));
+return rc;
+}else{
+clear_simulated_io_error();
+memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
+}
+}else{
+TEST_INCR(pPager->nRead);
+}
+}
+/* Link the page into the page hash table */
+h = pgno & (pPager->nHash-1);
+assert( pgno!=0 );
+pPg->pNextHash = pPager->aHash[h];
+pPager->aHash[h] = pPg;
+if( pPg->pNextHash ){
+assert( pPg->pNextHash->pPrevHash==0 );
+pPg->pNextHash->pPrevHash = pPg;
+}
+#ifdef SQLITE_CHECK_PAGES
+pPg->pageHash = pager_pagehash(pPg);
+#endif
+}else{
+/* The requested page is in the page cache. */
+TEST_INCR(pPager->nHit);
+page_ref(pPg);
+}
+*ppPage = PGHDR_TO_DATA(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 sqlite3pager_get().  The difference between this routine
+** and sqlite3pager_get() 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.
+*/
+void *sqlite3pager_lookup(Pager *pPager, Pgno pgno){
+PgHdr *pPg;
+assert( pPager!=0 );
+assert( pgno!=0 );
+if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
+return 0;
+}
+pPg = pager_lookup(pPager, pgno);
+if( pPg==0 ) return 0;
+page_ref(pPg);
+return PGHDR_TO_DATA(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 sqlite3pager_unref(void *pData){
+PgHdr *pPg;
+/* Decrement the reference count for this page
+*/
+pPg = DATA_TO_PGHDR(pData);
+assert( pPg->nRef>0 );
+pPg->nRef--;
+REFINFO(pPg);
+CHECK_PAGE(pPg);
+/* When the number of references to a page reach 0, call the
+** destructor and add the page to the freelist.
+*/
+if( pPg->nRef==0 ){
+Pager *pPager;
+pPager = pPg->pPager;
+pPg->pNextFree = 0;
+pPg->pPrevFree = pPager->pLast;
+pPager->pLast = pPg;
+if( pPg->pPrevFree ){
+pPg->pPrevFree->pNextFree = pPg;
+}else{
+pPager->pFirst = pPg;
+}
+if( pPg->needSync==0 && pPager->pFirstSynced==0 ){
+pPager->pFirstSynced = pPg;
+}
+if( pPager->xDestructor ){
+pPager->xDestructor(pData, pPager->pageSize);
+}
+/* When all pages reach the freelist, drop the read lock from
+** the database file.
+*/
+pPager->nRef--;
+assert( pPager->nRef>=0 );
+if( pPager->nRef==0 && !MEMDB ){
+pager_reset(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){
+int rc;
+assert( !MEMDB );
+assert( pPager->state>=PAGER_RESERVED );
+assert( pPager->journalOpen==0 );
+assert( pPager->useJournal );
+assert( pPager->aInJournal==0 );
+sqlite3pager_pagecount(pPager);
+pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
+if( pPager->aInJournal==0 ){
+rc = SQLITE_NOMEM;
+goto failed_to_open_journal;
+}
+rc = sqlite3OsOpenExclusive(pPager->zJournal, &pPager->jfd,
+pPager->tempFile);
+pPager->journalOff = 0;
+pPager->setMaster = 0;
+pPager->journalHdr = 0;
+if( rc!=SQLITE_OK ){
+goto failed_to_open_journal;
+}
+sqlite3OsSetFullSync(pPager->jfd, pPager->full_fsync);
+sqlite3OsSetFullSync(pPager->fd, pPager->full_fsync);
+sqlite3OsOpenDirectory(pPager->jfd, pPager->zDirectory);
+pPager->journalOpen = 1;
+pPager->journalStarted = 0;
+pPager->needSync = 0;
+pPager->alwaysRollback = 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 = sqlite3pager_stmt_begin(pPager);
+}
+if( rc!=SQLITE_OK && rc!=SQLITE_NOMEM ){
+rc = pager_unwritelock(pPager);
+if( rc==SQLITE_OK ){
+rc = SQLITE_FULL;
+}
+}
+return rc;
+failed_to_open_journal:
+sqliteFree(pPager->aInJournal);
+pPager->aInJournal = 0;
+if( rc==SQLITE_NOMEM ){
+/* If this was a malloc() failure, then we will not be closing the pager
+** file. So delete any journal file we may have just created. Otherwise,
+** the system will get confused, we have a read-lock on the file and a
+** mysterious journal has appeared in the filesystem.
+*/
+sqlite3OsDelete(pPager->zJournal);
+}else{
+sqlite3OsUnlock(pPager->fd, NO_LOCK);
+pPager->state = PAGER_UNLOCK;
+}
+return rc;
+}
+/*
+** Acquire a write-lock on the database.  The lock is removed when
+** the any of the following happen:
+**
+**   *  sqlite3pager_commit() is called.
+**   *  sqlite3pager_rollback() is called.
+**   *  sqlite3pager_close() is called.
+**   *  sqlite3pager_unref() 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 sqlite3pager_begin(void *pData, int exFlag){
+PgHdr *pPg = DATA_TO_PGHDR(pData);
+Pager *pPager = pPg->pPager;
+int rc = SQLITE_OK;
+assert( pPg->nRef>0 );
+assert( pPager->state!=PAGER_UNLOCK );
+if( pPager->state==PAGER_SHARED ){
+assert( pPager->aInJournal==0 );
+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;
+TRACE2("TRANSACTION %d\n", PAGERID(pPager));
+if( pPager->useJournal && !pPager->tempFile ){
+rc = pager_open_journal(pPager);
+}
+}
+}
+return rc;
+}
+/*
+** Make a page dirty.  Set its dirty flag and add it to the dirty
+** page list.
+*/
+static void makeDirty(PgHdr *pPg){
+if( pPg->dirty==0 ){
+Pager *pPager = pPg->pPager;
+pPg->dirty = 1;
+pPg->pDirty = pPager->pDirty;
+if( pPager->pDirty ){
+pPager->pDirty->pPrevDirty = pPg;
+}
+pPg->pPrevDirty = 0;
+pPager->pDirty = pPg;
+}
+}
+/*
+** Make a page clean.  Clear its dirty bit and remove it from the
+** dirty page list.
+*/
+static void makeClean(PgHdr *pPg){
+if( pPg->dirty ){
+pPg->dirty = 0;
+if( pPg->pDirty ){
+pPg->pDirty->pPrevDirty = pPg->pPrevDirty;
+}
+if( pPg->pPrevDirty ){
+pPg->pPrevDirty->pDirty = pPg->pDirty;
+}else{
+pPg->pPager->pDirty = pPg->pDirty;
+}
+}
+}
+/*
+** 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 sqlite3pager_commit() or sqlite3pager_rollback() to
+** reset.
+*/
+int sqlite3pager_write(void *pData){
+PgHdr *pPg = DATA_TO_PGHDR(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);
+/* 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->inJournal && (pPg->inStmt || pPager->stmtInUse==0) ){
+pPager->dirtyCache = 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 = sqlite3pager_begin(pData, 0);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+assert( pPager->state>=PAGER_RESERVED );
+if( !pPager->journalOpen && pPager->useJournal ){
+rc = pager_open_journal(pPager);
+if( rc!=SQLITE_OK ) return rc;
+}
+assert( pPager->journalOpen || !pPager->useJournal );
+pPager->dirtyCache = 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->inJournal && (pPager->useJournal || MEMDB) ){
+if( (int)pPg->pgno <= pPager->origDbSize ){
+int szPg;
+if( MEMDB ){
+PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+TRACE3("JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
+assert( pHist->pOrig==0 );
+pHist->pOrig = sqliteMallocRaw( pPager->pageSize );
+if( pHist->pOrig ){
+memcpy(pHist->pOrig, PGHDR_TO_DATA(pPg), pPager->pageSize);
+}
+}else{
+u32 cksum, saved;
+char *pData2, *pEnd;
+/* 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);
+pEnd = pData2 + pPager->pageSize;
+pData2 -= 4;
+saved = *(u32*)pEnd;
+put32bits(pEnd, cksum);
+szPg = pPager->pageSize+8;
+put32bits(pData2, pPg->pgno);
+rc = sqlite3OsWrite(pPager->jfd, pData2, szPg);
+pPager->journalOff += szPg;
+TRACE4("JOURNAL %d page %d needSync=%d\n",
+PAGERID(pPager), pPg->pgno, pPg->needSync);
+*(u32*)pEnd = saved;
+	  /* 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->aInJournal!=0 );
+pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
+pPg->needSync = !pPager->noSync;
+if( pPager->stmtInUse ){
+pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
+page_add_to_stmt_list(pPg);
+}
+}
+}else{
+pPg->needSync = !pPager->journalStarted && !pPager->noSync;
+TRACE4("APPEND %d page %d needSync=%d\n",
+PAGERID(pPager), pPg->pgno, pPg->needSync);
+}
+if( pPg->needSync ){
+pPager->needSync = 1;
+}
+pPg->inJournal = 1;
+}
+/* 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 && !pPg->inStmt && (int)pPg->pgno<=pPager->stmtSize ){
+assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
+if( MEMDB ){
+PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+assert( pHist->pStmt==0 );
+pHist->pStmt = sqliteMallocRaw( pPager->pageSize );
+if( pHist->pStmt ){
+memcpy(pHist->pStmt, PGHDR_TO_DATA(pPg), pPager->pageSize);
+}
+TRACE3("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
+}else{
+char *pData2 = CODEC2(pPager, pData, pPg->pgno, 7)-4;
+put32bits(pData2, pPg->pgno);
+rc = sqlite3OsWrite(pPager->stfd, pData2, pPager->pageSize+4);
+TRACE3("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
+if( rc!=SQLITE_OK ){
+return rc;
+}
+pPager->stmtNRec++;
+assert( pPager->aInStmt!=0 );
+pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
+}
+page_add_to_stmt_list(pPg);
+}
+}
+/* Update the database size and return.
+*/
+if( pPager->dbSize<(int)pPg->pgno ){
+pPager->dbSize = pPg->pgno;
+if( !MEMDB && pPager->dbSize==PENDING_BYTE/pPager->pageSize ){
+pPager->dbSize++;
+}
+}
+return rc;
+}
+/*
+** Return TRUE if the page given in the argument was previously passed
+** to sqlite3pager_write().  In other words, return TRUE if it is ok
+** to change the content of the page.
+*/
+#ifndef NDEBUG
+int sqlite3pager_iswriteable(void *pData){
+PgHdr *pPg = DATA_TO_PGHDR(pData);
+return pPg->dirty;
+}
+#endif
+#ifndef SQLITE_OMIT_VACUUM
+/*
+** Replace the content of a single page with the information in the third
+** argument.
+*/
+int sqlite3pager_overwrite(Pager *pPager, Pgno pgno, void *pData){
+void *pPage;
+int rc;
+rc = sqlite3pager_get(pPager, pgno, &pPage);
+if( rc==SQLITE_OK ){
+rc = sqlite3pager_write(pPage);
+if( rc==SQLITE_OK ){
+memcpy(pPage, pData, pPager->pageSize);
+}
+sqlite3pager_unref(pPage);
+}
+return rc;
+}
+#endif
+/*
+** A call to this routine tells the pager that it is not necessary to
+** write the information on page "pgno" 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
+** sqlite3pager_dont_rollback() 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 sqlite3pager_dont_rollback() 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 dont_rollback() routine is called.  But because the page contains
+** critical data, we still need to be sure it gets rolled back in spite
+** of the dont_rollback() call.
+*/
+void sqlite3pager_dont_write(Pager *pPager, Pgno pgno){
+PgHdr *pPg;
+if( MEMDB ) return;
+pPg = pager_lookup(pPager, pgno);
+assert( pPg!=0 );  /* We never call _dont_write unless the page is in mem */
+pPg->alwaysRollback = 1;
+if( pPg->dirty && !pPager->stmtInUse ){
+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{
+TRACE3("DONT_WRITE page %d of %d\n", pgno, PAGERID(pPager));
+makeClean(pPg);
+#ifdef SQLITE_CHECK_PAGES
+pPg->pageHash = pager_pagehash(pPg);
+#endif
+}
+}
+}
+/*
+** 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.
+*/
+void sqlite3pager_dont_rollback(void *pData){
+PgHdr *pPg = DATA_TO_PGHDR(pData);
+Pager *pPager = pPg->pPager;
+if( pPager->state!=PAGER_EXCLUSIVE || pPager->journalOpen==0 ) return;
+if( pPg->alwaysRollback || pPager->alwaysRollback || MEMDB ) return;
+if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
+assert( pPager->aInJournal!=0 );
+pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
+pPg->inJournal = 1;
+if( pPager->stmtInUse ){
+pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
+page_add_to_stmt_list(pPg);
+}
+TRACE3("DONT_ROLLBACK page %d of %d\n", pPg->pgno, PAGERID(pPager));
+}
+if( pPager->stmtInUse && !pPg->inStmt && (int)pPg->pgno<=pPager->stmtSize ){
+assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
+assert( pPager->aInStmt!=0 );
+pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
+page_add_to_stmt_list(pPg);
+}
+}
+/*
+** 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 sqlite3pager_commit(Pager *pPager){
+int rc;
+PgHdr *pPg;
+if( pPager->errCode ){
+return pPager->errCode;
+}
+if( pPager->state<PAGER_RESERVED ){
+return SQLITE_ERROR;
+}
+TRACE2("COMMIT %d\n", PAGERID(pPager));
+if( MEMDB ){
+pPg = pager_get_all_dirty_pages(pPager);
+while( pPg ){
+clearHistory(PGHDR_TO_HIST(pPg, pPager));
+pPg->dirty = 0;
+pPg->inJournal = 0;
+pPg->inStmt = 0;
+pPg->needSync = 0;
+pPg->pPrevStmt = pPg->pNextStmt = 0;
+pPg = pPg->pDirty;
+}
+pPager->pDirty = 0;
+#ifndef NDEBUG
+for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
+PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+assert( !pPg->alwaysRollback );
+assert( !pHist->pOrig );
+assert( !pHist->pStmt );
+}
+#endif
+pPager->pStmt = 0;
+pPager->state = PAGER_SHARED;
+return SQLITE_OK;
+}
+if( pPager->dirtyCache==0 ){
+/* Exit early (without doing the time-consuming sqlite3OsSync() calls)
+** if there have been no changes to the database file. */
+assert( pPager->needSync==0 );
+rc = pager_unwritelock(pPager);
+pPager->dbSize = -1;
+return rc;
+}
+assert( pPager->journalOpen );
+rc = sqlite3pager_sync(pPager, 0, 0);
+if( rc==SQLITE_OK ){
+rc = pager_unwritelock(pPager);
+pPager->dbSize = -1;
+}
+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 (SQLITE_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 sqlite3pager_rollback(Pager *pPager){
+int rc;
+TRACE2("ROLLBACK %d\n", PAGERID(pPager));
+if( MEMDB ){
+PgHdr *p;
+for(p=pPager->pAll; p; p=p->pNextAll){
+PgHistory *pHist;
+assert( !p->alwaysRollback );
+if( !p->dirty ){
+assert( !((PgHistory *)PGHDR_TO_HIST(p, pPager))->pOrig );
+assert( !((PgHistory *)PGHDR_TO_HIST(p, pPager))->pStmt );
+continue;
+}
+pHist = PGHDR_TO_HIST(p, pPager);
+if( pHist->pOrig ){
+memcpy(PGHDR_TO_DATA(p), pHist->pOrig, pPager->pageSize);
+TRACE3("ROLLBACK-PAGE %d of %d\n", p->pgno, PAGERID(pPager));
+}else{
+TRACE3("PAGE %d is clean on %d\n", p->pgno, PAGERID(pPager));
+}
+clearHistory(pHist);
+p->dirty = 0;
+p->inJournal = 0;
+p->inStmt = 0;
+p->pPrevStmt = p->pNextStmt = 0;
+if( pPager->xReiniter ){
+pPager->xReiniter(PGHDR_TO_DATA(p), pPager->pageSize);
+}
+}
+pPager->pDirty = 0;
+pPager->pStmt = 0;
+pPager->dbSize = pPager->origDbSize;
+memoryTruncate(pPager);
+pPager->stmtInUse = 0;
+pPager->state = PAGER_SHARED;
+return SQLITE_OK;
+}
+if( !pPager->dirtyCache || !pPager->journalOpen ){
+rc = pager_unwritelock(pPager);
+pPager->dbSize = -1;
+return rc;
+}
+if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
+if( pPager->state>=PAGER_EXCLUSIVE ){
+pager_playback(pPager);
+}
+return pPager->errCode;
+}
+if( pPager->state==PAGER_RESERVED ){
+int rc2;
+rc = pager_reload_cache(pPager);
+rc2 = pager_unwritelock(pPager);
+if( rc==SQLITE_OK ){
+rc = rc2;
+}
+}else{
+rc = pager_playback(pPager);
+}
+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.
+*/
+return pager_error(pPager, rc);
+}
+/*
+** Return TRUE if the database file is opened read-only.  Return FALSE
+** if the database is (in theory) writable.
+*/
+int sqlite3pager_isreadonly(Pager *pPager){
+return pPager->readOnly;
+}
+/*
+** Return the number of references to the pager.
+*/
+int sqlite3pager_refcount(Pager *pPager){
+return pPager->nRef;
+}
+#ifdef SQLITE_TEST
+/*
+** This routine is used for testing and analysis only.
+*/
+int *sqlite3pager_stats(Pager *pPager){
+static int a[11];
+a[0] = pPager->nRef;
+a[1] = pPager->nPage;
+a[2] = pPager->mxPage;
+a[3] = pPager->dbSize;
+a[4] = pPager->state;
+a[5] = pPager->errCode;
+a[6] = pPager->nHit;
+a[7] = pPager->nMiss;
+a[8] = pPager->nOvfl;
+a[9] = pPager->nRead;
+a[10] = pPager->nWrite;
+return a;
+}
+#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.
+*/
+int sqlite3pager_stmt_begin(Pager *pPager){
+int rc;
+char zTemp[SQLITE_TEMPNAME_SIZE];
+assert( !pPager->stmtInUse );
+assert( pPager->dbSize>=0 );
+TRACE2("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 );
+pPager->aInStmt = sqliteMalloc( pPager->dbSize/8 + 1 );
+if( pPager->aInStmt==0 ){
+/* sqlite3OsLock(pPager->fd, SHARED_LOCK); */
+return SQLITE_NOMEM;
+}
+#ifndef NDEBUG
+rc = sqlite3OsFileSize(pPager->jfd, &pPager->stmtJSize);
+if( rc ) goto stmt_begin_failed;
+assert( pPager->stmtJSize == pPager->journalOff );
+#endif
+pPager->stmtJSize = pPager->journalOff;
+pPager->stmtSize = pPager->dbSize;
+pPager->stmtHdrOff = 0;
+pPager->stmtCksum = pPager->cksumInit;
+if( !pPager->stmtOpen ){
+rc = sqlite3pager_opentemp(zTemp, &pPager->stfd);
+if( rc ) goto stmt_begin_failed;
+pPager->stmtOpen = 1;
+pPager->stmtNRec = 0;
+}
+pPager->stmtInUse = 1;
+return SQLITE_OK;
+stmt_begin_failed:
+if( pPager->aInStmt ){
+sqliteFree(pPager->aInStmt);
+pPager->aInStmt = 0;
+}
+return rc;
+}
+/*
+** Commit a statement.
+*/
+int sqlite3pager_stmt_commit(Pager *pPager){
+if( pPager->stmtInUse ){
+PgHdr *pPg, *pNext;
+TRACE2("STMT-COMMIT %d\n", PAGERID(pPager));
+if( !MEMDB ){
+sqlite3OsSeek(pPager->stfd, 0);
+/* sqlite3OsTruncate(pPager->stfd, 0); */
+sqliteFree( pPager->aInStmt );
+pPager->aInStmt = 0;
+}
+for(pPg=pPager->pStmt; pPg; pPg=pNext){
+pNext = pPg->pNextStmt;
+assert( pPg->inStmt );
+pPg->inStmt = 0;
+pPg->pPrevStmt = pPg->pNextStmt = 0;
+if( MEMDB ){
+PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+sqliteFree(pHist->pStmt);
+pHist->pStmt = 0;
+}
+}
+pPager->stmtNRec = 0;
+pPager->stmtInUse = 0;
+pPager->pStmt = 0;
+}
+pPager->stmtAutoopen = 0;
+return SQLITE_OK;
+}
+/*
+** Rollback a statement.
+*/
+int sqlite3pager_stmt_rollback(Pager *pPager){
+int rc;
+if( pPager->stmtInUse ){
+TRACE2("STMT-ROLLBACK %d\n", PAGERID(pPager));
+if( MEMDB ){
+PgHdr *pPg;
+for(pPg=pPager->pStmt; pPg; pPg=pPg->pNextStmt){
+PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+if( pHist->pStmt ){
+memcpy(PGHDR_TO_DATA(pPg), pHist->pStmt, pPager->pageSize);
+sqliteFree(pHist->pStmt);
+pHist->pStmt = 0;
+}
+}
+pPager->dbSize = pPager->stmtSize;
+memoryTruncate(pPager);
+rc = SQLITE_OK;
+}else{
+rc = pager_stmt_playback(pPager);
+}
+sqlite3pager_stmt_commit(pPager);
+}else{
+rc = SQLITE_OK;
+}
+pPager->stmtAutoopen = 0;
+return rc;
+}
+/*
+** Return the full pathname of the database file.
+*/
+const char *sqlite3pager_filename(Pager *pPager){
+return pPager->zFilename;
+}
+/*
+** Return the directory of the database file.
+*/
+const char *sqlite3pager_dirname(Pager *pPager){
+return pPager->zDirectory;
+}
+/*
+** Return the full pathname of the journal file.
+*/
+const char *sqlite3pager_journalname(Pager *pPager){
+return pPager->zJournal;
+}
+/*
+** Return true if fsync() calls are disabled for this pager.  Return FALSE
+** if fsync()s are executed normally.
+*/
+int sqlite3pager_nosync(Pager *pPager){
+return pPager->noSync;
+}
+/*
+** Set the codec for this pager
+*/
+void sqlite3pager_set_codec(
+Pager *pPager,
+void *(*xCodec)(void*,void*,Pgno,int),
+void *pCodecArg
+){
+pPager->xCodec = xCodec;
+pPager->pCodecArg = pCodecArg;
+}
+/*
+** 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){
+void *pPage;
+PgHdr *pPgHdr;
+u32 change_counter;
+int rc;
+/* Open page 1 of the file for writing. */
+rc = sqlite3pager_get(pPager, 1, &pPage);
+if( rc!=SQLITE_OK ) return rc;
+rc = sqlite3pager_write(pPage);
+if( rc!=SQLITE_OK ) return rc;
+/* Read the current value at byte 24. */
+pPgHdr = DATA_TO_PGHDR(pPage);
+change_counter = retrieve32bits(pPgHdr, 24);
+/* Increment the value just read and write it back to byte 24. */
+change_counter++;
+put32bits(((char*)PGHDR_TO_DATA(pPgHdr))+24, change_counter);
+/* Release the page reference. */
+sqlite3pager_unref(pPage);
+return SQLITE_OK;
+}
+/*
+** 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 sqlite3pager_sync() call.
+**
+** If parameter nTrunc is non-zero, then the pager file is truncated to
+** nTrunc pages (this is used by auto-vacuum databases).
+*/
+int sqlite3pager_sync(Pager *pPager, const char *zMaster, Pgno nTrunc){
+int rc = SQLITE_OK;
+TRACE4("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;
+assert( pPager->journalOpen );
+/* 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);
+if( rc!=SQLITE_OK ) goto sync_exit;
+#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;
+void *pPage;
+int iSkip = PAGER_MJ_PGNO(pPager);
+for( i=nTrunc+1; i<=pPager->origDbSize; i++ ){
+if( !(pPager->aInJournal[i/8] & (1<<(i&7))) && i!=iSkip ){
+rc = sqlite3pager_get(pPager, i, &pPage);
+if( rc!=SQLITE_OK ) goto sync_exit;
+rc = sqlite3pager_write(pPage);
+sqlite3pager_unref(pPage);
+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 = sqlite3pager_truncate(pPager, nTrunc);
+if( rc!=SQLITE_OK ) goto sync_exit;
+}
+#endif
+/* Write all dirty pages to the database file */
+pPg = pager_get_all_dirty_pages(pPager);
+rc = pager_write_pagelist(pPg);
+if( rc!=SQLITE_OK ) goto sync_exit;
+/* Sync the database file. */
+if( !pPager->noSync ){
+rc = sqlite3OsSync(pPager->fd, 0);
+}
+pPager->state = PAGER_SYNCED;
+}else if( MEMDB && nTrunc!=0 ){
+rc = sqlite3pager_truncate(pPager, nTrunc);
+}
+sync_exit:
+return rc;
+}
+#ifndef SQLITE_OMIT_AUTOVACUUM
+/*
+** Move the page identified by pData to location pgno in the file.
+**
+** There must be no references to the current page pgno. If current page
+** pgno is not already in the rollback journal, it is not written there by
+** by this routine. The same applies to the page pData refers to on entry to
+** this routine.
+**
+** References to the page refered to by pData remain valid. Updating any
+** meta-data associated with page pData (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).
+*/
+int sqlite3pager_movepage(Pager *pPager, void *pData, Pgno pgno){
+PgHdr *pPg = DATA_TO_PGHDR(pData);
+PgHdr *pPgOld;
+int h;
+Pgno needSyncPgno = 0;
+assert( pPg->nRef>0 );
+TRACE5("MOVE %d page %d (needSync=%d) moves to %d\n",
+PAGERID(pPager), pPg->pgno, pPg->needSync, pgno);
+if( pPg->needSync ){
+needSyncPgno = pPg->pgno;
+assert( pPg->inJournal );
+assert( pPg->dirty );
+assert( pPager->needSync );
+}
+/* Unlink pPg from it's hash-chain */
+unlinkHashChain(pPager, pPg);
+/* If the cache contains a page with page-number pgno, remove it
+** from it's 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.
+*/
+pPgOld = pager_lookup(pPager, pgno);
+if( pPgOld ){
+assert( pPgOld->nRef==0 );
+unlinkHashChain(pPager, pPgOld);
+makeClean(pPgOld);
+if( pPgOld->needSync ){
+assert( pPgOld->inJournal );
+pPg->inJournal = 1;
+pPg->needSync = 1;
+assert( pPager->needSync );
+}
+}
+/* Change the page number for pPg and insert it into the new hash-chain. */
+assert( pgno!=0 );
+pPg->pgno = pgno;
+h = pgno & (pPager->nHash-1);
+if( pPager->aHash[h] ){
+assert( pPager->aHash[h]->pPrevHash==0 );
+pPager->aHash[h]->pPrevHash = pPg;
+}
+pPg->pNextHash = pPager->aHash[h];
+pPager->aHash[h] = pPg;
+pPg->pPrevHash = 0;
+makeDirty(pPg);
+pPager->dirtyCache = 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
+** Pager.aInJournal bit has been set. This needs to be remedied by loading
+** the page into the pager-cache and setting the PgHdr.needSync flag.
+**
+** The sqlite3pager_get() call may cause the journal to sync. So make
+** sure the Pager.needSync flag is set too.
+*/
+int rc;
+void *pNeedSync;
+assert( pPager->needSync );
+rc = sqlite3pager_get(pPager, needSyncPgno, &pNeedSync);
+if( rc!=SQLITE_OK ) return rc;
+pPager->needSync = 1;
+DATA_TO_PGHDR(pNeedSync)->needSync = 1;
+DATA_TO_PGHDR(pNeedSync)->inJournal = 1;
+makeDirty(DATA_TO_PGHDR(pNeedSync));
+sqlite3pager_unref(pNeedSync);
+}
+return SQLITE_OK;
+}
+#endif
+#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
+/*
+** Return the current state of the file lock for the given pager.
+** The return value is one of NO_LOCK, SHARED_LOCK, RESERVED_LOCK,
+** PENDING_LOCK, or EXCLUSIVE_LOCK.
+*/
+int sqlite3pager_lockstate(Pager *pPager){
+return sqlite3OsLockState(pPager->fd);
+}
+#endif
+#ifdef SQLITE_DEBUG
+/*
+** Print a listing of all referenced pages and their ref count.
+*/
+void sqlite3pager_refdump(Pager *pPager){
+PgHdr *pPg;
+for(pPg=pPager->pAll; pPg; pPg=pPg->pNextAll){
+if( pPg->nRef<=0 ) continue;
+sqlite3DebugPrintf("PAGE %3d addr=%p nRef=%d\n",
+pPg->pgno, PGHDR_TO_DATA(pPg), pPg->nRef);
+}
+}
+#endif
+#endif /* SQLITE_OMIT_DISKIO */