Move SQLite from src/chrome/third_party to src/third_party

since it will be shared with WebCore and Gears in the
future.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@1586 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 4578 insertions, 0 deletions

diff --git a/third_party/sqlite/pager.c b/third_party/sqlite/pager.c
new file mode 100644
index 0000000..b2d16158
--- /dev/null
+++ b/third_party/sqlite/pager.c
@@ -0,0 +1,4578 @@
+/*
+** 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 1.355 2007/08/11 00:26:21 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 sqlite3DebugPrintf printf
+#define PAGERTRACE1(X)       sqlite3DebugPrintf(X)
+#define PAGERTRACE2(X,Y)     sqlite3DebugPrintf(X,Y)
+#define PAGERTRACE3(X,Y,Z)   sqlite3DebugPrintf(X,Y,Z)
+#define PAGERTRACE4(X,Y,Z,W) sqlite3DebugPrintf(X,Y,Z,W)
+#define PAGERTRACE5(X,Y,Z,W,V) sqlite3DebugPrintf(X,Y,Z,W,V)
+#else
+#define PAGERTRACE1(X)
+#define PAGERTRACE2(X,Y)
+#define PAGERTRACE3(X,Y,Z)
+#define PAGERTRACE4(X,Y,Z,W)
+#define PAGERTRACE5(X,Y,Z,W,V)
+#endif
+
+/*
+** The following two macros are used within the PAGERTRACEX() macros above
+** to print out file-descriptors. 
+**
+** PAGERID() takes a pointer to a Pager struct as 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 or
+**                       truncate the journal file and the transaction 
+**                       will be committed.
+**
+** The page cache comes up in PAGER_UNLOCK.  The first time a
+** sqlite3PagerGet() occurs, the state transitions to PAGER_SHARED.
+** After all pages have been released using sqlite_page_unref(),
+** the state transitions back to PAGER_UNLOCK.  The first time
+** that sqlite3PagerWrite() is called, the state transitions to
+** PAGER_RESERVED.  (Note that sqlite3PagerWrite() can only be
+** called on an outstanding page which means that the pager must
+** be in PAGER_SHARED before it transitions to PAGER_RESERVED.)
+** PAGER_RESERVED means that there is an open rollback journal.
+** The transition to PAGER_EXCLUSIVE occurs before any changes
+** are made to the database file, though writes to the rollback
+** journal occurs with just PAGER_RESERVED.  After an sqlite3PagerRollback()
+** or sqlite3PagerCommitPhaseTwo(), the state can go back to PAGER_SHARED,
+** or it can stay at PAGER_EXCLUSIVE if we are in exclusive access mode.
+*/
+#define PAGER_UNLOCK      0
+#define PAGER_SHARED      1   /* same as SHARED_LOCK */
+#define PAGER_RESERVED    2   /* same as RESERVED_LOCK */
+#define PAGER_EXCLUSIVE   4   /* same as EXCLUSIVE_LOCK */
+#define PAGER_SYNCED      5
+
+/*
+** If the SQLITE_BUSY_RESERVED_LOCK macro is set to true at compile-time,
+** then failed attempts to get a reserved lock will invoke the busy callback.
+** This is off by default.  To see why, consider the following scenario:
+** 
+** Suppose thread A already has a shared lock and wants a reserved lock.
+** Thread B already has a reserved lock and wants an exclusive lock.  If
+** both threads are using their busy callbacks, it might be a long time
+** be for one of the threads give up and allows the other to proceed.
+** But if the thread trying to get the reserved lock gives up quickly
+** (if it never invokes its busy callback) then the contention will be
+** resolved quickly.
+*/
+#ifndef SQLITE_BUSY_RESERVED_LOCK
+# define SQLITE_BUSY_RESERVED_LOCK 0
+#endif
+
+/*
+** This macro rounds values up so that if the value is an address it
+** is guaranteed to be an address that is aligned to an 8-byte boundary.
+*/
+#define FORCE_ALIGNMENT(X)   (((X)+7)&~7)
+
+/*
+** 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 sqlite3PagerWrite() on a page prior to making
+** any modifications to that page.  The first time sqlite3PagerWrite()
+** 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 sqlite3PagerWrite() is called and
+** is cleared again when the page content is written back to the original
+** database file.
+**
+** Details of important structure elements:
+**
+** needSync
+**
+**     If this is true, this means that it is not safe to write the page
+**     content to the database because the original content needed
+**     for rollback has not by synced to the main rollback journal.
+**     The original content may have been written to the rollback journal
+**     but it has not yet been synced.  So we cannot write to the database
+**     file because power failure might cause the page in the journal file
+**     to never reach the disk.  It is as if the write to the journal file
+**     does not occur until the journal file is synced.
+**     
+**     This flag is false if the page content exactly matches what
+**     currently exists in the database file.  The needSync flag is also
+**     false if the original content has been written to the main rollback
+**     journal and synced.  If the page represents a new page that has
+**     been added onto the end of the database during the current
+**     transaction, the needSync flag is true until the original database
+**     size in the journal header has been synced to disk.
+**
+** inJournal
+**
+**     This is true if the original page has been written into the main
+**     rollback journal.  This is always false for new pages added to
+**     the end of the database file during the current transaction.
+**     And this flag says nothing about whether or not the journal
+**     has been synced to disk.  For pages that are in the original
+**     database file, the following expression should always be true:
+**
+**       inJournal = (pPager->aInJournal[(pgno-1)/8] & (1<<((pgno-1)%8))!=0
+**
+**     The pPager->aInJournal[] array is only valid for the original
+**     pages of the database, not new pages that are added to the end
+**     of the database, so obviously the above expression cannot be
+**     valid for new pages.  For new pages inJournal is always 0.
+**
+** dirty
+**
+**     When true, this means that the content of the page has been
+**     modified and needs to be written back to the database file.
+**     If false, it means that either the content of the page is
+**     unchanged or else the content is unimportant and we do not
+**     care whether or not it is preserved.
+**
+** alwaysRollback
+**
+**     This means that the sqlite3PagerDontRollback() API should be
+**     ignored for this page.  The DontRollback() API attempts to say
+**     that the content of the page on disk is unimportant (it is an
+**     unused page on the freelist) so that it is unnecessary to 
+**     rollback changes to this page because the content of the page
+**     can change without changing the meaning of the database.  This
+**     flag overrides any DontRollback() attempt.  This flag is set
+**     when a page that originally contained valid data is added to
+**     the freelist.  Later in the same transaction, this page might
+**     be pulled from the freelist and reused for something different
+**     and at that point the DontRollback() API will be called because
+**     pages taken from the freelist do not need to be protected by
+**     the rollback journal.  But this flag says that the page was
+**     not originally part of the freelist so that it still needs to
+**     be rolled back in spite of any subsequent DontRollback() calls.
+**
+** needRead 
+**
+**     This flag means (when true) that the content of the page has
+**     not yet been loaded from disk.  The in-memory content is just
+**     garbage.  (Actually, we zero the content, but you should not
+**     make any assumptions about the content nevertheless.)  If the
+**     content is needed in the future, it should be read from 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 */
+  u8 inJournal;                  /* TRUE if has been written to journal */
+  u8 dirty;                      /* TRUE if we need to write back changes */
+  u8 needSync;                   /* Sync journal before writing this page */
+  u8 alwaysRollback;             /* Disable DontRollback() for this page */
+  u8 needRead;                   /* Read content if PagerWrite() is called */
+  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 */
+  PgHdr *pNextStmt, *pPrevStmt;  /* List of pages in the statement journal */
+  u8 inStmt;                     /* TRUE if in the statement subjournal */
+};
+
+/*
+** 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, or
+** or SQLITE_FULL. Once one of the first three errors occurs, it persists
+** and is returned as the result of every major pager API call.  The
+** SQLITE_FULL return code is slightly different. It persists only until the
+** next successful rollback is performed on the pager cache. Also,
+** SQLITE_FULL does not affect the sqlite3PagerGet() and sqlite3PagerLookup()
+** APIs, they may still be used successfully.
+*/
+struct Pager {
+  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 tempFile;                /* zFilename is a temporary file */
+  u8 readOnly;                /* True for a read-only database */
+  u8 needSync;                /* True if an fsync() is needed on the journal */
+  u8 dirtyCache;              /* True if cached pages have changed */
+  u8 alwaysRollback;          /* Disable DontRollback() for all pages */
+  u8 memDb;                   /* True to inhibit all file I/O */
+  u8 setMaster;               /* True if a m-j name has been written to jrnl */
+  u8 doNotSync;               /* Boolean. While true, do not spill the cache */
+  u8 exclusiveMode;           /* Boolean. True if locking_mode==EXCLUSIVE */
+  u8 changeCountDone;         /* Set after incrementing the change-counter */
+  int errCode;                /* One of several kinds of errors */
+  int dbSize;                 /* Number of pages in the file */
+  int origDbSize;             /* dbSize before the current change */
+  int stmtSize;               /* Size of database (in pages) at stmt_begin() */
+  int nRec;                   /* Number of pages written to the journal */
+  u32 cksumInit;              /* Quasi-random value added to every checksum */
+  int stmtNRec;               /* Number of records in stmt subjournal */
+  int nExtra;                 /* Add this many bytes to each in-memory page */
+  int pageSize;               /* Number of bytes in a page */
+  int nPage;                  /* Total number of in-memory pages */
+  int nRef;                   /* Number of in-memory pages with PgHdr.nRef>0 */
+  int mxPage;                 /* Maximum number of pages to hold in cache */
+  Pgno mxPgno;                /* Maximum allowed size of the database */
+  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;            /* Cache hits and missing */
+  int nRead, nWrite;          /* Database pages read/written */
+#endif
+  void (*xDestructor)(DbPage*,int); /* Call this routine when freeing pages */
+  void (*xReiniter)(DbPage*,int);   /* Call this routine when reloading pages */
+#ifdef SQLITE_HAS_CODEC
+  void *(*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
+  void *pCodecArg;            /* First argument to xCodec() */
+#endif
+  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
+  char *pTmpSpace;            /* Pager.pageSize bytes of space for tmp use */
+  char dbFileVers[16];        /* Changes whenever database file changes */
+};
+
+/*
+** The following global variables hold counters used for
+** testing purposes only.  These variables do not exist in
+** a non-testing build.  These variables are not thread-safe.
+*/
+#ifdef SQLITE_TEST
+int sqlite3_pager_readdb_count = 0;    /* Number of full pages read from DB */
+int sqlite3_pager_writedb_count = 0;   /* Number of full pages written to DB */
+int sqlite3_pager_writej_count = 0;    /* Number of pages written to journal */
+int sqlite3_pager_pgfree_count = 0;    /* Number of cache pages freed */
+# define PAGER_INCR(v)  v++
+#else
+# define PAGER_INCR(v)
+#endif
+
+
+
+/*
+** Journal files begin with the following magic string.  The data
+** was obtained from /dev/random.  It is used only as a sanity check.
+**
+** Since version 2.8.0, the journal format contains additional sanity
+** checking information.  If the power fails while the journal is begin
+** written, semi-random garbage data might appear in the journal
+** file after power is restored.  If an attempt is then made
+** to roll the journal back, the database could be corrupted.  The additional
+** sanity checking data is an attempt to discover the garbage in the
+** journal and ignore it.
+**
+** The sanity checking information for the new journal format consists
+** of a 32-bit checksum on each page of data.  The checksum covers both
+** the page number and the pPager->pageSize bytes of data for the page.
+** This cksum is initialized to a 32-bit random value that appears in the
+** journal file right after the header.  The random initializer is important,
+** because garbage data that appears at the end of a journal is likely
+** data that was once in other files that have now been deleted.  If the
+** garbage data came from an obsolete journal file, the checksums might
+** be correct.  But by initializing the checksum to random value which
+** is different for every journal, we minimize that risk.
+*/
+static const unsigned char aJournalMagic[] = {
+  0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7,
+};
+
+/*
+** The size of the header and of each page in the journal is determined
+** by the following macros.
+*/
+#define JOURNAL_PG_SZ(pPager)  ((pPager->pageSize) + 8)
+
+/*
+** The journal header size for this pager. In the future, this could be
+** set to some value read from the disk controller. The important
+** characteristic is that it is the same size as a disk sector.
+*/
+#define JOURNAL_HDR_SZ(pPager) (pPager->sectorSize)
+
+/*
+** The macro MEMDB is true if we are dealing with an in-memory database.
+** We do this as a macro so that if the SQLITE_OMIT_MEMORYDB macro is set,
+** the value of MEMDB will be a constant and the compiler will optimize
+** out code that would never execute.
+*/
+#ifdef SQLITE_OMIT_MEMORYDB
+# define MEMDB 0
+#else
+# define MEMDB pPager->memDb
+#endif
+
+/*
+** Page number PAGER_MJ_PGNO is never used in an SQLite database (it is
+** reserved for working around a windows/posix incompatibility). It is
+** used in the journal to signify that the remainder of the journal file 
+** is devoted to storing a master journal name - there are no more pages to
+** roll back. See comments for function writeMasterJournal() for details.
+*/
+/* #define PAGER_MJ_PGNO(x) (PENDING_BYTE/((x)->pageSize)) */
+#define PAGER_MJ_PGNO(x) ((PENDING_BYTE/((x)->pageSize))+1)
+
+/*
+** The maximum legal page number is (2^31 - 1).
+*/
+#define PAGER_MAX_PGNO 2147483647
+
+/* See comments above the definition. */
+int sqlite3PagerAcquire2(
+  Pager *pPager,
+  Pgno pgno,
+  DbPage **ppPage,
+  int noContent,
+  unsigned char *pDataToFill);
+
+/*
+** Enable reference count tracking (for debugging) here:
+*/
+#ifdef SQLITE_DEBUG
+  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=%-3d total=%d\n",
+       p->pgno, PGHDR_TO_DATA(p), p->nRef, p->pPager->nRef
+    );
+    cnt++;   /* Something to set a breakpoint on */
+  }
+# define REFINFO(X)  pager_refinfo(X)
+#else
+# define REFINFO(X)
+#endif
+
+/*
+** Return true if page *pPg has already been written to the statement
+** journal (or statement snapshot has been created, if *pPg is part
+** of an in-memory database).
+*/
+static int pageInStatement(PgHdr *pPg){
+  Pager *pPager = pPg->pPager;
+  if( MEMDB ){
+    return PGHDR_TO_HIST(pPg, pPager)->inStmt;
+  }else{
+    Pgno pgno = pPg->pgno;
+    u8 *a = pPager->aInStmt;
+    return (a && (int)pgno<=pPager->stmtSize && (a[pgno/8] & (1<<(pgno&7))));
+  }
+}
+
+/*
+** 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 = sqlite3Get4byte(ac);
+  }
+  return rc;
+}
+
+/*
+** Write a 32-bit integer into a string buffer in big-endian byte order.
+*/
+#define put32bits(A,B)  sqlite3Put4byte((u8*)A,B)
+
+/*
+** Write a 32-bit integer into the given file descriptor.  Return SQLITE_OK
+** on success or an error code is something goes wrong.
+*/
+static int write32bits(OsFile *fd, u32 val){
+  char ac[4];
+  put32bits(ac, val);
+  return sqlite3OsWrite(fd, ac, 4);
+}
+
+/*
+** This function should be called when an error occurs within the pager
+** code. The first argument is a pointer to the pager structure, the
+** second the error-code about to be returned by a pager API function. 
+** The value returned is a copy of the second argument to this function. 
+**
+** If the second argument is SQLITE_IOERR, SQLITE_CORRUPT, or SQLITE_FULL
+** the error becomes persistent. All subsequent API calls on this Pager
+** will immediately return the same error code.
+*/
+static int pager_error(Pager *pPager, int rc){
+  int rc2 = rc & 0xff;
+  assert(
+       pPager->errCode==SQLITE_FULL ||
+       pPager->errCode==SQLITE_OK ||
+       (pPager->errCode & 0xff)==SQLITE_IOERR
+  );
+  if(
+    rc2==SQLITE_FULL ||
+    rc2==SQLITE_IOERR ||
+    rc2==SQLITE_CORRUPT
+  ){
+    pPager->errCode = rc;
+  }
+  return rc;
+}
+
+/*
+** If SQLITE_CHECK_PAGES is defined then we do some sanity checking
+** on the cache using a hash function.  This is used for testing
+** and debugging only.
+*/
+#ifdef SQLITE_CHECK_PAGES
+/*
+** Return a 32-bit hash of the page data for pPage.
+*/
+static u32 pager_datahash(int nByte, unsigned char *pData){
+  u32 hash = 0;
+  int i;
+  for(i=0; i<nByte; i++){
+    hash = (hash*1039) + pData[i];
+  }
+  return hash;
+}
+static u32 pager_pagehash(PgHdr *pPage){
+  return pager_datahash(pPage->pPager->pageSize, 
+                        (unsigned char *)PGHDR_TO_DATA(pPage));
+}
+
+/*
+** The CHECK_PAGE macro takes a PgHdr* as an argument. If SQLITE_CHECK_PAGES
+** is defined, and NDEBUG is not defined, an assert() statement checks
+** that the page is either dirty or still matches the calculated page-hash.
+*/
+#define CHECK_PAGE(x) checkPage(x)
+static void checkPage(PgHdr *pPg){
+  Pager *pPager = pPg->pPager;
+  assert( !pPg->pageHash || pPager->errCode || MEMDB || pPg->dirty || 
+      pPg->pageHash==pager_pagehash(pPg) );
+}
+
+#else
+#define pager_datahash(X,Y)  0
+#define pager_pagehash(X)  0
+#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;
+
+  if( pPager->stmtHdrOff==0 ){
+    pPager->stmtHdrOff = pPager->journalOff;
+  }
+
+  rc = seekJournalHdr(pPager);
+  if( rc ) return rc;
+
+  pPager->journalHdr = pPager->journalOff;
+  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);
+  IOTRACE(("JHDR %p %lld %d\n", pPager, pPager->journalHdr, sizeof(zHeader)))
+  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 ){
+    IOTRACE(("JTAIL %p %lld\n", pPager, pPager->journalOff-1))
+    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 sqlite3PagerStmtCommit()
+** 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;
+  PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+  assert( MEMDB );
+  if( !pHist->inStmt ){
+    assert( pHist->pPrevStmt==0 && pHist->pNextStmt==0 );
+    if( pPager->pStmt ){
+      PGHDR_TO_HIST(pPager->pStmt, pPager)->pPrevStmt = pPg;
+    }
+    pHist->pNextStmt = pPager->pStmt;
+    pPager->pStmt = pPg;
+    pHist->inStmt = 1;
+  }
+}
+
+/*
+** 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 file.
+*/
+static void pager_unlock(Pager *pPager){
+  if( !pPager->exclusiveMode ){
+    if( !MEMDB ){
+      sqlite3OsUnlock(pPager->fd, NO_LOCK);
+      pPager->dbSize = -1;
+      IOTRACE(("UNLOCK %p\n", pPager))
+    }
+    pPager->state = PAGER_UNLOCK;
+    pPager->changeCountDone = 0;
+  }
+}
+
+/*
+** Execute a rollback if a transaction is active and unlock the 
+** database file. This is a no-op if the pager has already entered
+** the error-state.
+*/
+static void pagerUnlockAndRollback(Pager *p){
+  if( p->errCode ) return;
+  assert( p->state>=PAGER_RESERVED || p->journalOpen==0 );
+  if( p->state>=PAGER_RESERVED ){
+    sqlite3PagerRollback(p);
+  }
+  pager_unlock(p);
+  assert( p->errCode || !p->journalOpen || (p->exclusiveMode&&!p->journalOff) );
+  assert( p->errCode || !p->stmtOpen || p->exclusiveMode );
+}
+
+
+/*
+** 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){
+    IOTRACE(("PGFREE %p %d\n", pPager, pPg->pgno));
+    PAGER_INCR(sqlite3_pager_pgfree_count);
+    pNext = pPg->pNextAll;
+    sqliteFree(pPg);
+  }
+  pPager->pStmt = 0;
+  pPager->pFirst = 0;
+  pPager->pFirstSynced = 0;
+  pPager->pLast = 0;
+  pPager->pAll = 0;
+  pPager->nHash = 0;
+  sqliteFree(pPager->aHash);
+  pPager->nPage = 0;
+  pPager->aHash = 0;
+  pPager->nRef = 0;
+}
+
+/*
+** This routine ends a transaction.  A transaction is ended by either
+** a COMMIT or a ROLLBACK.
+**
+** When this routine is called, the pager has the journal file open and
+** a RESERVED or EXCLUSIVE lock on the database.  This routine will release
+** the database lock and acquires a SHARED lock in its place if that is
+** the appropriate thing to do.  Release locks usually is appropriate,
+** unless we are in exclusive access mode or unless this is a 
+** COMMIT AND BEGIN or ROLLBACK AND BEGIN operation.
+**
+** The journal file is either deleted or truncated.
+**
+** TODO: Consider keeping the journal file open for temporary databases.
+** This might give a performance improvement on windows where opening
+** a file is an expensive operation.
+*/
+static int pager_end_transaction(Pager *pPager){
+  PgHdr *pPg;
+  int rc = SQLITE_OK;
+  int rc2 = SQLITE_OK;
+  assert( !MEMDB );
+  if( pPager->state<PAGER_RESERVED ){
+    return SQLITE_OK;
+  }
+  sqlite3PagerStmtCommit(pPager);
+  if( pPager->stmtOpen && !pPager->exclusiveMode ){
+    sqlite3OsClose(&pPager->stfd);
+    pPager->stmtOpen = 0;
+  }
+  if( pPager->journalOpen ){
+    if( pPager->exclusiveMode 
+          && (rc = sqlite3OsTruncate(pPager->jfd, 0))==SQLITE_OK ){;
+      sqlite3OsSeek(pPager->jfd, 0);
+      pPager->journalOff = 0;
+      pPager->journalStarted = 0;
+    }else{
+      sqlite3OsClose(&pPager->jfd);
+      pPager->journalOpen = 0;
+      if( rc==SQLITE_OK ){
+        rc = 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;
+      pPg->alwaysRollback = 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 );
+  }
+
+  if( !pPager->exclusiveMode ){
+    rc2 = sqlite3OsUnlock(pPager->fd, SHARED_LOCK);
+    pPager->state = PAGER_SHARED;
+  }else if( pPager->state==PAGER_SYNCED ){
+    pPager->state = PAGER_EXCLUSIVE;
+  }
+  pPager->origDbSize = 0;
+  pPager->setMaster = 0;
+  pPager->needSync = 0;
+  pPager->pFirstSynced = pPager->pFirst;
+  pPager->dbSize = -1;
+
+  return (rc==SQLITE_OK?rc2:rc);
+}
+
+/*
+** Compute and return a checksum for the page of data.
+**
+** This is not a real checksum.  It is really just the sum of the 
+** random initial value and the page number.  We experimented with
+** a checksum of the entire data, but that was found to be too slow.
+**
+** Note that the page number is stored at the beginning of data and
+** the checksum is stored at the end.  This is important.  If journal
+** corruption occurs due to a power failure, the most likely scenario
+** is that one end or the other of the record will be changed.  It is
+** much less likely that the two ends of the journal record will be
+** correct and the middle be corrupt.  Thus, this "checksum" scheme,
+** though fast and simple, catches the mostly likely kind of corruption.
+**
+** FIX ME:  Consider adding every 200th (or so) byte of the data to the
+** checksum.  That way if a single page spans 3 or more disk sectors and
+** only the middle sector is corrupt, we will still have a reasonable
+** chance of failing the checksum and thus detecting the problem.
+*/
+static u32 pager_cksum(Pager *pPager, const u8 *aData){
+  u32 cksum = pPager->cksumInit;
+  int i = pPager->pageSize-200;
+  while( i>0 ){
+    cksum += aData[i];
+    i -= 200;
+  }
+  return cksum;
+}
+
+/* Forward declaration */
+static void makeClean(PgHdr*);
+
+/*
+** Read a single page from the journal file opened on file descriptor
+** jfd.  Playback this one page.
+**
+** 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 = (u8 *)pPager->pTmpSpace;   /* 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) );
+  assert( aData );
+
+  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.
+  **
+  ** An exception to the above rule: If the database is in no-sync mode
+  ** and a page is moved during an incremental vacuum then the page may
+  ** not be in the pager cache. Later: if a malloc() or IO error occurs
+  ** during a Movepage() call, then the page may not be in the cache
+  ** either. So the condition described in the above paragraph is not
+  ** assert()able.
+  **
+  ** If in EXCLUSIVE state, then we update the pager cache if it exists
+  ** and the main file. The page is then marked not dirty.
+  **
+  ** Ticket #1171:  The statement journal might contain page content that is
+  ** different from the page content at the start of the transaction.
+  ** This occurs when a page is changed prior to the start of a statement
+  ** then changed again within the statement.  When rolling back such a
+  ** statement we must not write to the original database unless we know
+  ** for certain that original page contents are synced into the main rollback
+  ** journal.  Otherwise, a power loss might leave modified data in the
+  ** database file without an entry in the rollback journal that can
+  ** restore the database to its original form.  Two conditions must be
+  ** met before writing to the database files. (1) the database must be
+  ** locked.  (2) we know that the original page content is fully synced
+  ** in the main journal either because the page is not in cache or else
+  ** the page is marked as needSync==0.
+  */
+  pPg = pager_lookup(pPager, pgno);
+  PAGERTRACE4("PLAYBACK %d page %d hash(%08x)\n",
+               PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, aData));
+  if( pPager->state>=PAGER_EXCLUSIVE && (pPg==0 || 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
+    ** sqlite3PagerRollback().
+    */
+    void *pData;
+    /* assert( pPg->nRef==0 || pPg->pgno==1 ); */
+    pData = PGHDR_TO_DATA(pPg);
+    memcpy(pData, aData, pPager->pageSize);
+    if( pPager->xReiniter ){
+      pPager->xReiniter(pPg, pPager->pageSize);
+    }
+#ifdef SQLITE_CHECK_PAGES
+    pPg->pageHash = pager_pagehash(pPg);
+#endif
+    /* If this was page 1, then restore the value of Pager.dbFileVers.
+    ** Do this before any decoding. */
+    if( pgno==1 ){
+      memcpy(&pPager->dbFileVers, &((u8*)pData)[24],sizeof(pPager->dbFileVers));
+    }
+
+    /* Decode the page just read from disk */
+    CODEC1(pPager, pData, pPg->pgno, 3);
+  }
+  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);
+  assert( rc!=SQLITE_OK || 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);
+        assert( rc!=SQLITE_OK || 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);
+    }
+  }
+  
+  rc = sqlite3OsDelete(zMaster);
+
+delmaster_out:
+  if( zMasterJournal ){
+    sqliteFree(zMasterJournal);
+  }  
+  if( master_open ){
+    sqlite3OsClose(&master);
+  }
+  return rc;
+}
+
+
+static void pager_truncate_cache(Pager *pPager);
+
+/*
+** Truncate the main file of the given pager to the number of pages
+** indicated. Also truncate the cached representation of the file.
+*/
+static int pager_truncate(Pager *pPager, int nPage){
+  int rc = SQLITE_OK;
+  if( pPager->state>=PAGER_EXCLUSIVE ){
+    rc = sqlite3OsTruncate(pPager->fd, pPager->pageSize*(i64)nPage);
+  }
+  if( rc==SQLITE_OK ){
+    pPager->dbSize = nPage;
+    pager_truncate_cache(pPager);
+  }
+  return rc;
+}
+
+/*
+** Set the sectorSize for the given pager.
+**
+** The sector size is the larger of the sector size reported
+** by sqlite3OsSectorSize() and the pageSize.
+*/
+static void setSectorSize(Pager *pPager){
+  pPager->sectorSize = sqlite3OsSectorSize(pPager->fd);
+  if( pPager->sectorSize<pPager->pageSize ){
+    pPager->sectorSize = pPager->pageSize;
+  }
+}
+
+/*
+** 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, int isHot){
+  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 || szJ==0 ){
+    goto end_playback;
+  }
+
+  /* Read the master journal name from the journal, if it is present.
+  ** If a master journal file name is specified, but the file is not
+  ** present on disk, then the journal is not hot and does not need to be
+  ** played back.
+  */
+  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 nRec is 0 and this rollback is of a transaction created by this
+    ** process and if this is the final header in the journal, then it means
+    ** that this part of the journal was being filled but has not yet been
+    ** synced to disk.  Compute the number of pages based on the remaining
+    ** size of the file.
+    **
+    ** The third term of the test was added to fix ticket #2565.
+    */
+    if( nRec==0 && !isHot &&
+        pPager->journalHdr+JOURNAL_HDR_SZ(pPager)==pPager->journalOff ){
+      nRec = (szJ - pPager->journalOff) / JOURNAL_PG_SZ(pPager);
+    }
+
+    /* If this is the first header read from the journal, truncate the
+    ** database file back to it's original size.
+    */
+    if( pPager->journalOff==JOURNAL_HDR_SZ(pPager) ){
+      rc = pager_truncate(pPager, mxPg);
+      if( rc!=SQLITE_OK ){
+        goto end_playback;
+      }
+    }
+
+    /* Copy original pages out of the journal and back into the database file.
+    */
+    for(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_end_transaction(pPager);
+  }
+  if( zMaster ){
+    /* If there was a master journal and this routine will return success,
+    ** 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 sector size
+  ** value. Reset it to the correct value for this process.
+  */
+  setSectorSize(pPager);
+  return rc;
+}
+
+/*
+** Playback the statement journal.
+**
+** This is similar to playing back the transaction journal but with
+** a few extra twists.
+**
+**    (1)  The number of pages in the database file at the start of
+**         the statement is stored in pPager->stmtSize, not in the
+**         journal file itself.
+**
+**    (2)  In addition to playing back the statement journal, also
+**         playback all pages of the transaction journal beginning
+**         at offset pPager->stmtJSize.
+*/
+static int pager_stmt_playback(Pager *pPager){
+  i64 szJ;                 /* Size of the full journal */
+  i64 hdrOff;
+  int nRec;                /* Number of Records */
+  int i;                   /* Loop counter */
+  int rc;
+
+  szJ = pPager->journalOff;
+#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 just after the end of the last journal
+  ** page written before the first journal-header for this statement
+  ** transaction was written, or the end of the file if no journal
+  ** header was written.
+  */
+  hdrOff = pPager->stmtHdrOff;
+  assert( pPager->fullSync || !hdrOff );
+  if( !hdrOff ){
+    hdrOff = szJ;
+  }
+  
+  /* Truncate the database back to its original size.
+  */
+  rc = pager_truncate(pPager, pPager->stmtSize);
+  assert( pPager->state>=PAGER_SHARED );
+
+  /* Figure out how many records are in the statement journal.
+  */
+  assert( pPager->stmtInUse && pPager->journalOpen );
+  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;
+  while( pPager->journalOff < hdrOff ){
+    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 sqlite3PagerSetCachesize(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 sqlite3PagerSetSafetyLevel(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 file descriptor into *fd.  Return SQLITE_OK on success or some
+** other error code if we fail.
+**
+** The OS will automatically delete the temporary file when it is
+** closed.
+*/
+static int sqlite3PagerOpentemp(OsFile **pFd){
+  int cnt = 8;
+  int rc;
+  char zFile[SQLITE_TEMPNAME_SIZE];
+
+#ifdef SQLITE_TEST
+  sqlite3_opentemp_count++;  /* Used for testing and analysis only */
+#endif
+  do{
+    cnt--;
+    sqlite3OsTempFileName(zFile);
+    rc = sqlite3OsOpenExclusive(zFile, pFd, 1);
+    assert( rc!=SQLITE_OK || *pFd );
+  }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 sqlite3PagerGet() and is only held open until the
+** last page is released using sqlite3PagerUnref().
+**
+** If zFilename is NULL then a randomly-named temporary file is created
+** and used as the file to be cached.  The file will be deleted
+** automatically when it is closed.
+**
+** If zFilename is ":memory:" then all information is held in cache.
+** It is never written to disk.  This can be used to implement an
+** in-memory database.
+*/
+int sqlite3PagerOpen(
+  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 = 0;
+  int rc = SQLITE_OK;
+  int i;
+  int tempFile = 0;
+  int memDb = 0;
+  int readOnly = 0;
+  int useJournal = (flags & PAGER_OMIT_JOURNAL)==0;
+  int noReadlock = (flags & PAGER_NO_READLOCK)!=0;
+  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
+
+  /* We used to test if malloc() had already failed before proceeding. 
+  ** But the way this function is used in SQLite means that can never
+  ** happen. Furthermore, if the malloc-failed flag is already set, 
+  ** either the call to sqliteStrDup() or sqliteMalloc() below will
+  ** fail shortly and SQLITE_NOMEM returned anyway.
+  */
+  *ppPager = 0;
+
+  /* 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);
+        assert( rc!=SQLITE_OK || fd );
+      }
+    }
+  }else{
+    rc = sqlite3PagerOpentemp(&fd);
+    sqlite3OsTempFileName(zTemp);
+    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( pPager && rc==SQLITE_OK ){
+      pPager->pTmpSpace = (char *)sqliteMallocRaw(SQLITE_DEFAULT_PAGE_SIZE);
+    }
+  }
+
+
+  /* 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 || !pPager->pTmpSpace || rc!=SQLITE_OK ){
+    sqlite3OsClose(&fd);
+    sqliteFree(zFullPathname);
+    sqliteFree(pPager);
+    return ((rc==SQLITE_OK)?SQLITE_NOMEM:rc);
+  }
+
+  PAGERTRACE3("OPEN %d %s\n", FILEHANDLEID(fd), zFullPathname);
+  IOTRACE(("OPEN %p %s\n", pPager, zFullPathname))
+  pPager->zFilename = (char*)&pPager[1];
+  pPager->zDirectory = &pPager->zFilename[nameLen+1];
+  pPager->zJournal = &pPager->zDirectory[nameLen+1];
+  memcpy(pPager->zFilename, zFullPathname, nameLen+1);
+  memcpy(pPager->zDirectory, zFullPathname, nameLen+1);
+
+  for(i=nameLen; i>0 && pPager->zDirectory[i-1]!='/'; i--){}
+  if( i>0 ) pPager->zDirectory[i-1] = 0;
+  memcpy(pPager->zJournal, zFullPathname,nameLen);
+  sqliteFree(zFullPathname);
+  memcpy(&pPager->zJournal[nameLen], "-journal",sizeof("-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->mxPage = 100;
+  pPager->mxPgno = SQLITE_MAX_PAGE_COUNT;
+  assert( PAGER_UNLOCK==0 );
+  /* pPager->state = PAGER_UNLOCK; */
+  /* pPager->errMask = 0; */
+  pPager->tempFile = tempFile;
+  assert( tempFile==PAGER_LOCKINGMODE_NORMAL 
+          || tempFile==PAGER_LOCKINGMODE_EXCLUSIVE );
+  assert( PAGER_LOCKINGMODE_EXCLUSIVE==1 );
+  pPager->exclusiveMode = tempFile; 
+  pPager->memDb = memDb;
+  pPager->readOnly = readOnly;
+  /* pPager->needSync = 0; */
+  pPager->noSync = pPager->tempFile || !useJournal;
+  pPager->fullSync = (pPager->noSync?0:1);
+  /* pPager->pFirst = 0; */
+  /* pPager->pFirstSynced = 0; */
+  /* pPager->pLast = 0; */
+  pPager->nExtra = FORCE_ALIGNMENT(nExtra);
+  assert(fd||memDb);
+  if( !memDb ){
+    setSectorSize(pPager);
+  }
+  /* 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 sqlite3PagerSetBusyhandler(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 sqlite3PagerClose().  
+** Destructors are only called by sqlite3PagerUnref().
+*/
+void sqlite3PagerSetDestructor(Pager *pPager, void (*xDesc)(DbPage*,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 sqlite3PagerSetReiniter(Pager *pPager, void (*xReinit)(DbPage*,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 sqlite3PagerSetPagesize(Pager *pPager, int pageSize){
+  assert( pageSize>=512 && pageSize<=SQLITE_MAX_PAGE_SIZE );
+  if( !pPager->memDb && pPager->nRef==0 ){
+    pager_reset(pPager);
+    pPager->pageSize = pageSize;
+    pPager->pTmpSpace = sqlite3ReallocOrFree(pPager->pTmpSpace, pageSize);
+  }
+  return pPager->pageSize;
+}
+
+/*
+** Attempt to set the maximum database page count if mxPage is positive. 
+** Make no changes if mxPage is zero or negative.  And never reduce the
+** maximum page count below the current size of the database.
+**
+** Regardless of mxPage, return the current maximum page count.
+*/
+int sqlite3PagerMaxPageCount(Pager *pPager, int mxPage){
+  if( mxPage>0 ){
+    pPager->mxPgno = mxPage;
+  }
+  sqlite3PagerPagecount(pPager);
+  return pPager->mxPgno;
+}
+
+/*
+** The following set of routines are used to disable the simulated
+** I/O error mechanism.  These routines are used to avoid simulated
+** errors in places where we do not care about errors.
+**
+** Unless -DSQLITE_TEST=1 is used, these routines are all no-ops
+** and generate no code.
+*/
+#ifdef SQLITE_TEST
+extern int sqlite3_io_error_pending;
+extern int sqlite3_io_error_hit;
+static int saved_cnt;
+void disable_simulated_io_errors(void){
+  saved_cnt = sqlite3_io_error_pending;
+  sqlite3_io_error_pending = -1;
+}
+void enable_simulated_io_errors(void){
+  sqlite3_io_error_pending = saved_cnt;
+}
+#else
+# define disable_simulated_io_errors()
+# define enable_simulated_io_errors()
+#endif
+
+/*
+** Read the first N bytes from the beginning of the file into memory
+** that pDest points to. 
+**
+** No error checking is done. The rational for this is that this function 
+** may be called even if the file does not exist or contain a header. In 
+** these cases sqlite3OsRead() will return an error, to which the correct 
+** response is to zero the memory at pDest and continue.  A real IO error 
+** will presumably recur and be picked up later (Todo: Think about this).
+*/
+int sqlite3PagerReadFileheader(Pager *pPager, int N, unsigned char *pDest){
+  int rc = SQLITE_OK;
+  memset(pDest, 0, N);
+  if( MEMDB==0 ){
+    disable_simulated_io_errors();
+    sqlite3OsSeek(pPager->fd, 0);
+    enable_simulated_io_errors();
+    IOTRACE(("DBHDR %p 0 %d\n", pPager, N))
+    rc = sqlite3OsRead(pPager->fd, pDest, N);
+    if( rc==SQLITE_IOERR_SHORT_READ ){
+      rc = SQLITE_OK;
+    }
+  }
+  return rc;
+}
+
+/*
+** Return the total number of pages in the disk file associated with
+** pPager. 
+**
+** If the PENDING_BYTE lies on the page directly after the end of the
+** file, then consider this page part of the file too. For example, if
+** PENDING_BYTE is byte 4096 (the first byte of page 5) and the size of the
+** file is 4096 bytes, 5 is returned instead of 4.
+*/
+int sqlite3PagerPagecount(Pager *pPager){
+  i64 n;
+  int rc;
+  assert( pPager!=0 );
+  if( pPager->errCode ){
+    return 0;
+  }
+  if( pPager->dbSize>=0 ){
+    n = pPager->dbSize;
+  }else{
+    if( (rc = sqlite3OsFileSize(pPager->fd, &n))!=SQLITE_OK ){
+      pager_error(pPager, rc);
+      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++;
+  }
+  if( n>pPager->mxPgno ){
+    pPager->mxPgno = 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
+** sqlite3PagerMovepage() 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);
+}
+
+/*
+** This routine is used to truncate the cache when a database
+** is truncated.  Drop from the cache all pages whose pgno is
+** larger than pPager->dbSize and is unreferenced.
+**
+** Referenced pages larger than pPager->dbSize are zeroed.
+**
+** Actually, at the point this routine is called, it would be
+** an error to have a referenced page.  But rather than delete
+** that page and guarantee a subsequent segfault, it seems better
+** to zero it and hope that we error out sanely.
+*/
+static void pager_truncate_cache(Pager *pPager){
+  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;
+      IOTRACE(("PGFREE %p %d\n", pPager, pPg->pgno));
+      PAGER_INCR(sqlite3_pager_pgfree_count);
+      unlinkPage(pPg);
+      makeClean(pPg);
+      sqliteFree(pPg);
+      pPager->nPage--;
+    }
+  }
+}
+
+/*
+** Try to obtain a lock on a file.  Invoke the busy callback if the lock
+** is currently not available.  Repeat until the busy callback returns
+** false or until the lock succeeds.
+**
+** Return SQLITE_OK on success and an error code if we cannot obtain
+** the lock.
+*/
+static int pager_wait_on_lock(Pager *pPager, int locktype){
+  int rc;
+
+  /* The OS lock values must be the same as the Pager lock values */
+  assert( PAGER_SHARED==SHARED_LOCK );
+  assert( PAGER_RESERVED==RESERVED_LOCK );
+  assert( PAGER_EXCLUSIVE==EXCLUSIVE_LOCK );
+
+  /* If the file is currently unlocked then the size must be unknown */
+  assert( pPager->state>=PAGER_SHARED || pPager->dbSize<0 || MEMDB );
+
+  if( pPager->state>=locktype ){
+    rc = SQLITE_OK;
+  }else{
+    do {
+      rc = sqlite3OsLock(pPager->fd, locktype);
+    }while( rc==SQLITE_BUSY && sqlite3InvokeBusyHandler(pPager->pBusyHandler) );
+    if( rc==SQLITE_OK ){
+      pPager->state = locktype;
+      IOTRACE(("LOCK %p %d\n", pPager, locktype))
+    }
+  }
+  return rc;
+}
+
+/*
+** Truncate the file to the number of pages specified.
+*/
+int sqlite3PagerTruncate(Pager *pPager, Pgno nPage){
+  int rc;
+  assert( pPager->state>=PAGER_SHARED || MEMDB );
+  sqlite3PagerPagecount(pPager);
+  if( pPager->errCode ){
+    rc = pPager->errCode;
+    return rc;
+  }
+  if( nPage>=(unsigned)pPager->dbSize ){
+    return SQLITE_OK;
+  }
+  if( MEMDB ){
+    pPager->dbSize = nPage;
+    pager_truncate_cache(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);
+  return rc;
+}
+
+/*
+** Shutdown the page cache.  Free all memory and close all files.
+**
+** If a transaction was in progress when this routine is called, that
+** transaction is rolled back.  All outstanding pages are invalidated
+** and their memory is freed.  Any attempt to use a page associated
+** with this page cache after this function returns will likely
+** result in a coredump.
+**
+** This function always succeeds. If a transaction is active an attempt
+** is made to roll it back. If an error occurs during the rollback 
+** a hot journal may be left in the filesystem but no error is returned
+** to the caller.
+*/
+int sqlite3PagerClose(Pager *pPager){
+#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
+
+  disable_simulated_io_errors();
+  pPager->errCode = 0;
+  pPager->exclusiveMode = 0;
+  pager_reset(pPager);
+  pagerUnlockAndRollback(pPager);
+  enable_simulated_io_errors();
+  PAGERTRACE2("CLOSE %d\n", PAGERID(pPager));
+  IOTRACE(("CLOSE %p\n", 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->pTmpSpace);
+  sqliteFree(pPager);
+  return SQLITE_OK;
+}
+
+#if !defined(NDEBUG) || defined(SQLITE_TEST)
+/*
+** Return the page number for the given page data.
+*/
+Pgno sqlite3PagerPagenumber(DbPage *p){
+  return p->pgno;
+}
+#endif
+
+/*
+** 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 sqlite3PagerRef(DbPage *pPg){
+  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 ){
+          PAGERTRACE2("SYNC journal of %d\n", PAGERID(pPager));
+          IOTRACE(("JSYNC %p\n", pPager))
+          rc = sqlite3OsSync(pPager->jfd, 0);
+          if( rc!=0 ) return rc;
+        }
+        rc = sqlite3OsSeek(pPager->jfd,
+                           pPager->journalHdr + sizeof(aJournalMagic));
+        if( rc ) return rc;
+        IOTRACE(("JHDR %p %lld %d\n", pPager,
+                  pPager->journalHdr + sizeof(aJournalMagic), 4))
+        rc = write32bits(pPager->jfd, pPager->nRec);
+        if( rc ) return rc;
+
+        rc = sqlite3OsSeek(pPager->jfd, pPager->journalOff);
+        if( rc ) return rc;
+      }
+      PAGERTRACE2("SYNC journal of %d\n", PAGERID(pPager));
+      IOTRACE(("JSYNC %p\n", 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_ALLOC 25
+#define N_SORT_BUCKET       25
+#ifdef SQLITE_TEST
+  int sqlite3_pager_n_sort_bucket = 0;
+  #undef N_SORT_BUCKET
+  #define N_SORT_BUCKET \
+   (sqlite3_pager_n_sort_bucket?sqlite3_pager_n_sort_bucket:N_SORT_BUCKET_ALLOC)
+#endif
+static PgHdr *sort_pagelist(PgHdr *pIn){
+  PgHdr *a[N_SORT_BUCKET_ALLOC], *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 ){
+      /* Coverage: To get here, there need to be 2^(N_SORT_BUCKET) 
+      ** elements in the input list. This is possible, but impractical.
+      ** Testing this line is the point of global variable
+      ** sqlite3_pager_n_sort_bucket.
+      */
+      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 sqlite3PagerTruncate() was called to
+    ** make the file smaller (presumably by auto-vacuum code). Do not write
+    ** any such pages to the file.
+    */
+    if( pList->pgno<=pPager->dbSize ){
+      char *pData = CODEC2(pPager, PGHDR_TO_DATA(pList), pList->pgno, 6);
+      PAGERTRACE4("STORE %d page %d hash(%08x)\n",
+                   PAGERID(pPager), pList->pgno, pager_pagehash(pList));
+      IOTRACE(("PGOUT %p %d\n", pPager, pList->pgno));
+      rc = sqlite3OsWrite(pPager->fd, pData, pPager->pageSize);
+      PAGER_INCR(sqlite3_pager_writedb_count);
+      PAGER_INCR(pPager->nWrite);
+      if( pList->pgno==1 ){
+        memcpy(&pPager->dbFileVers, &pData[24], sizeof(pPager->dbFileVers));
+      }
+    }
+#ifndef NDEBUG
+    else{
+      PAGERTRACE3("NOSTORE %d page %d\n", PAGERID(pPager), pList->pgno);
+    }
+#endif
+    if( rc ) return rc;
+    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( sqlite3PagerPagecount(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;
+
+  assert(!MEMDB);
+
+  /* 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 );
+      assert( pPager->doNotSync==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
+  ** sqlite3PagerDontRollback() 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 ){
+    IOTRACE(("ALWAYS_ROLLBACK %p\n", pPager))
+    pPager->alwaysRollback = 1;
+  }
+
+  /* Unlink the old page from the free list and the hash table
+  */
+  unlinkPage(pPg);
+  assert( pPg->pgno==0 );
+
+  *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.
+*/
+#if defined(SQLITE_ENABLE_MEMORY_MANAGEMENT) && !defined(SQLITE_OMIT_DISKIO)
+int sqlite3PagerReleaseMemory(int nReq){
+  const ThreadData *pTsdro = sqlite3ThreadDataReadOnly();
+  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. */
+    Pager *pPager = pTsdro->pPager;
+    for( ; pPager && (nReq<0 || nReleased<nReq); pPager=pPager->pNext){
+      PgHdr *pPg;
+      int rc;
+
+      if( MEMDB ){
+        continue;
+      }
+
+      /* 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(pPager, 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 );
+        if( pPg==pPager->pAll ){
+           pPager->pAll = pPg->pNextAll;
+        }else{
+          for( pTmp=pPager->pAll; pTmp->pNextAll!=pPg; pTmp=pTmp->pNextAll ){}
+          pTmp->pNextAll = pPg->pNextAll;
+        }
+        nReleased += sqliteAllocSize(pPg);
+        IOTRACE(("PGFREE %p %d *\n", pPager, pPg->pgno));
+        PAGER_INCR(sqlite3_pager_pgfree_count);
+        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&0xff)==SQLITE_IOERR ||
+            rc==SQLITE_FULL ||
+            rc==SQLITE_BUSY
+        );
+        assert( pPager->state>=PAGER_RESERVED );
+        pager_error(pPager, rc);
+      }
+    }
+  }
+
+  return nReleased;
+}
+#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT && !SQLITE_OMIT_DISKIO */
+
+/*
+** Read the content of page pPg out of the database file.
+*/
+static int readDbPage(Pager *pPager, PgHdr *pPg, Pgno pgno){
+  int rc;
+  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);
+  }
+  PAGER_INCR(sqlite3_pager_readdb_count);
+  PAGER_INCR(pPager->nRead);
+  IOTRACE(("PGIN %p %d\n", pPager, pgno));
+  if( pgno==1 ){
+    memcpy(&pPager->dbFileVers, &((u8*)PGHDR_TO_DATA(pPg))[24],
+                                              sizeof(pPager->dbFileVers));
+  }
+  CODEC1(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
+  PAGERTRACE4("FETCH %d page %d hash(%08x)\n",
+               PAGERID(pPager), pPg->pgno, pager_pagehash(pPg));
+  return rc;
+}
+
+
+/*
+** This function is called to obtain the shared lock required before
+** data may be read from the pager cache. If the shared lock has already
+** been obtained, this function is a no-op.
+**
+** Immediately after obtaining the shared lock (if required), this function
+** checks for a hot-journal file. If one is found, an emergency rollback
+** is performed immediately.
+*/
+static int pagerSharedLock(Pager *pPager){
+  int rc = SQLITE_OK;
+
+  if( pPager->state==PAGER_UNLOCK ){
+    if( !MEMDB ){
+      assert( pPager->nRef==0 );
+      if( !pPager->noReadlock ){
+        rc = pager_wait_on_lock(pPager, SHARED_LOCK);
+        if( rc!=SQLITE_OK ){
+          return pager_error(pPager, rc);
+        }
+        assert( pPager->state>=SHARED_LOCK );
+      }
+  
+      /* If a journal file exists, and there is no RESERVED lock on the
+      ** database file, then it either needs to be played back or deleted.
+      */
+      if( 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 ){
+          pager_unlock(pPager);
+          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.
+        **
+        ** Open the journal for read/write access. This is because in 
+        ** exclusive-access mode the file descriptor will be kept open and
+        ** possibly used for a transaction later on. On some systems, the
+        ** OsTruncate() call used in exclusive-access mode also requires
+        ** a read/write file handle.
+        */
+        rc = SQLITE_BUSY;
+        if( sqlite3OsFileExists(pPager->zJournal) ){
+          int ro;
+          assert( !pPager->tempFile );
+          rc = sqlite3OsOpenReadWrite(pPager->zJournal, &pPager->jfd, &ro);
+          assert( rc!=SQLITE_OK || pPager->jfd );
+          if( ro ){
+            rc = SQLITE_BUSY;
+            sqlite3OsClose(&pPager->jfd);
+          }
+        }
+        if( rc!=SQLITE_OK ){
+          pager_unlock(pPager);
+          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, 1);
+        if( rc!=SQLITE_OK ){
+          return pager_error(pPager, rc);
+        }
+        assert(pPager->state==PAGER_SHARED || 
+            (pPager->exclusiveMode && pPager->state>PAGER_SHARED)
+        );
+      }
+
+      if( pPager->pAll ){
+        /* The shared-lock has just been acquired on the database file
+        ** and there are already pages in the cache (from a previous
+        ** read or write transaction).  Check to see if the database
+        ** has been modified.  If the database has changed, flush the
+        ** cache.
+        **
+        ** Database changes is detected by looking at 15 bytes beginning
+        ** at offset 24 into the file.  The first 4 of these 16 bytes are
+        ** a 32-bit counter that is incremented with each change.  The
+        ** other bytes change randomly with each file change when
+        ** a codec is in use.
+        ** 
+        ** There is a vanishingly small chance that a change will not be 
+        ** detected.  The chance of an undetected change is so small that
+        ** it can be neglected.
+        */
+        char dbFileVers[sizeof(pPager->dbFileVers)];
+        sqlite3PagerPagecount(pPager);
+
+        if( pPager->errCode ){
+          return pPager->errCode;
+        }
+
+        if( pPager->dbSize>0 ){
+          IOTRACE(("CKVERS %p %d\n", pPager, sizeof(dbFileVers)));
+          rc = sqlite3OsSeek(pPager->fd, 24);
+          if( rc!=SQLITE_OK ){
+            return rc;
+          }
+          rc = sqlite3OsRead(pPager->fd, &dbFileVers, sizeof(dbFileVers));
+          if( rc!=SQLITE_OK ){
+            return rc;
+          }
+        }else{
+          memset(dbFileVers, 0, sizeof(dbFileVers));
+        }
+
+        if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
+          pager_reset(pPager);
+        }
+      }
+    }
+    assert( pPager->exclusiveMode || pPager->state<=PAGER_SHARED );
+    if( pPager->state==PAGER_UNLOCK ){
+      pPager->state = PAGER_SHARED;
+    }
+  }
+
+  return rc;
+}
+
+/*
+** Allocate a PgHdr object.   Either create a new one or reuse
+** an existing one that is not otherwise in use.
+**
+** A new PgHdr structure is created if any of the following are
+** true:
+**
+**     (1)  We have not exceeded our maximum allocated cache size
+**          as set by the "PRAGMA cache_size" command.
+**
+**     (2)  There are no unused PgHdr objects available at this time.
+**
+**     (3)  This is an in-memory database.
+**
+**     (4)  There are no PgHdr objects that do not require a journal
+**          file sync and a sync of the journal file is currently
+**          prohibited.
+**
+** Otherwise, reuse an existing PgHdr.  In other words, reuse an
+** existing PgHdr if all of the following are true:
+**
+**     (1)  We have reached or exceeded the maximum cache size
+**          allowed by "PRAGMA cache_size".
+**
+**     (2)  There is a PgHdr available with PgHdr->nRef==0
+**
+**     (3)  We are not in an in-memory database
+**
+**     (4)  Either there is an available PgHdr that does not need
+**          to be synced to disk or else disk syncing is currently
+**          allowed.
+*/
+static int pagerAllocatePage(Pager *pPager, PgHdr **ppPg){
+  int rc = SQLITE_OK;
+  PgHdr *pPg;
+
+  /* Create a new PgHdr if any of the four conditions defined 
+  ** above is met: */
+  if( pPager->nPage<pPager->mxPage
+   || pPager->pFirst==0 
+   || MEMDB
+   || (pPager->pFirstSynced==0 && pPager->doNotSync)
+  ){
+    if( pPager->nPage>=pPager->nHash ){
+      pager_resize_hash_table(pPager,
+         pPager->nHash<256 ? 256 : pPager->nHash*2);
+      if( pPager->nHash==0 ){
+        rc = SQLITE_NOMEM;
+        goto pager_allocate_out;
+      }
+    }
+    pPg = sqliteMallocRaw( sizeof(*pPg) + pPager->pageSize
+                            + sizeof(u32) + pPager->nExtra
+                            + MEMDB*sizeof(PgHistory) );
+    if( pPg==0 ){
+      rc = SQLITE_NOMEM;
+      goto pager_allocate_out;
+    }
+    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++;
+  }else{
+    /* Recycle an existing page with a zero ref-count. */
+    rc = pager_recycle(pPager, 1, &pPg);
+    if( rc==SQLITE_BUSY ){
+      rc = SQLITE_IOERR_BLOCKED;
+    }
+    if( rc!=SQLITE_OK ){
+      goto pager_allocate_out;
+    }
+    assert( pPager->state>=SHARED_LOCK );
+    assert(pPg);
+  }
+  *ppPg = pPg;
+
+pager_allocate_out:
+  return rc;
+}
+
+/*
+** Make sure we have the content for a page.  If the page was
+** previously acquired with noContent==1, then the content was
+** just initialized to zeros instead of being read from disk.
+** But now we need the real data off of disk.  So make sure we
+** have it.  Read it in if we do not have it already.
+*/
+static int pager_get_content(PgHdr *pPg){
+  if( pPg->needRead ){
+    int rc = readDbPage(pPg->pPager, pPg, pPg->pgno);
+    if( rc==SQLITE_OK ){
+      pPg->needRead = 0;
+    }else{
+      return rc;
+    }
+  }
+  return SQLITE_OK;
+}
+
+/*
+** Acquire a page.
+**
+** A read lock on the disk file is obtained when the first page is acquired. 
+** This read lock is dropped when the last page is released.
+**
+** This routine works for any page number greater than 0.  If the database
+** file is smaller than the requested page, then no actual disk
+** read occurs and the memory image of the page is initialized to
+** all zeros.  The extra data appended to a page is always initialized
+** to zeros the first time a page is loaded into memory.
+**
+** The acquisition might fail for several reasons.  In all cases,
+** an appropriate error code is returned and *ppPage is set to NULL.
+**
+** See also sqlite3PagerLookup().  Both this routine and Lookup() attempt
+** to find a page in the in-memory cache first.  If the page is not already
+** in memory, this routine goes to disk to read it in whereas Lookup()
+** just returns 0.  This routine acquires a read-lock the first time it
+** has to go to disk, and could also playback an old journal if necessary.
+** Since Lookup() never goes to disk, it never has to deal with locks
+** or journal files.
+**
+** If noContent is false, the page contents are actually read from disk.
+** If noContent is true, it means that we do not care about the contents
+** of the page at this time, so do not do a disk read.  Just fill in the
+** page content with zeros.  But mark the fact that we have not read the
+** content by setting the PgHdr.needRead flag.  Later on, if 
+** sqlite3PagerWrite() is called on this page or if this routine is
+** called again with noContent==0, that means that the content is needed
+** and the disk read should occur at that point.
+*/
+int sqlite3PagerAcquire(
+  Pager *pPager,      /* The pager open on the database file */
+  Pgno pgno,          /* Page number to fetch */
+  DbPage **ppPage,    /* Write a pointer to the page here */
+  int noContent       /* Do not bother reading content from disk if true */
+){
+  /* This just passes through to our modified version with NULL data. */
+  return sqlite3PagerAcquire2(pPager, pgno, ppPage, noContent, 0);
+}
+
+/*
+** This is an internal version of sqlite3PagerAcquire that takes an extra
+** parameter of data to use to fill the page with. This allows more efficient
+** filling for preloaded data. If this extra parameter is NULL, we'll go to
+** the file.
+**
+** See sqlite3PagerLoadall which uses this function.
+*/
+int sqlite3PagerAcquire2(
+  Pager *pPager,      /* The pager open on the database file */
+  Pgno pgno,          /* Page number to fetch */
+  DbPage **ppPage,    /* Write a pointer to the page here */
+  int noContent,      /* Do not bother reading content from disk if true */
+  unsigned char* pDataToFill
+){
+  PgHdr *pPg;
+  int rc;
+
+  assert( pPager->state==PAGER_UNLOCK || pPager->nRef>0 || pgno==1 );
+
+  /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
+  ** number greater than this, or zero, is requested.
+  */
+  if( pgno>PAGER_MAX_PGNO || pgno==0 || pgno==PAGER_MJ_PGNO(pPager) ){
+    return SQLITE_CORRUPT_BKPT;
+  }
+
+  /* Make sure we have not hit any critical errors.
+  */ 
+  assert( pPager!=0 );
+  *ppPage = 0;
+  if( 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. pagerSharedLock() is a no-op if 
+  ** a database lock is already held.
+  */
+  rc = pagerSharedLock(pPager);
+  if( rc!=SQLITE_OK ){
+    return rc;
+  }
+  assert( pPager->state!=PAGER_UNLOCK );
+
+  pPg = pager_lookup(pPager, pgno);
+  if( pPg==0 ){
+    /* The requested page is not in the page cache. */
+    int nMax;
+    int h;
+    PAGER_INCR(pPager->nMiss);
+    rc = pagerAllocatePage(pPager, &pPg);
+    if( rc!=SQLITE_OK ){
+      return rc;
+    }
+
+    pPg->pgno = pgno;
+    assert( !MEMDB || pgno>pPager->stmtSize );
+    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;
+    }
+
+    makeClean(pPg);
+    pPg->nRef = 1;
+    REFINFO(pPg);
+
+    pPager->nRef++;
+    if( pPager->nExtra>0 ){
+      memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
+    }
+    nMax = sqlite3PagerPagecount(pPager);
+    if( pPager->errCode ){
+      sqlite3PagerUnref(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( nMax<(int)pgno || MEMDB || (noContent && !pPager->alwaysRollback) ){
+      if( pgno>pPager->mxPgno ){
+        sqlite3PagerUnref(pPg);
+        return SQLITE_FULL;
+      }
+      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
+      pPg->needRead = noContent && !pPager->alwaysRollback;
+      IOTRACE(("ZERO %p %d\n", pPager, pgno));
+    }else{
+      if (pDataToFill) {
+        /* Just copy from the given memory. */
+        memcpy(PGHDR_TO_DATA(pPg), pDataToFill, pPager->pageSize);
+        CODEC1(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
+      } else {
+        /* Load from disk (old regular sqlite code path). */
+        rc = readDbPage(pPager, pPg, pgno);
+        if( rc!=SQLITE_OK && rc!=SQLITE_IOERR_SHORT_READ ){
+          pPg->pgno = 0;
+          sqlite3PagerUnref(pPg);
+          return rc;
+        }
+      }
+      pPg->needRead = 0;
+    }
+
+    /* 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. */
+    assert(pPager->nRef>0 || pgno==1);
+    PAGER_INCR(pPager->nHit);
+    if( !noContent ){
+      rc = pager_get_content(pPg);
+      if( rc ){
+        return rc;
+      }
+    }
+    page_ref(pPg);
+  }
+  *ppPage = pPg;
+  return SQLITE_OK;
+}
+
+/*
+** Acquire a page if it is already in the in-memory cache.  Do
+** not read the page from disk.  Return a pointer to the page,
+** or 0 if the page is not in cache.
+**
+** See also sqlite3PagerGet().  The difference between this routine
+** and sqlite3PagerGet() is that _get() will go to the disk and read
+** in the page if the page is not already in cache.  This routine
+** returns NULL if the page is not in cache or if a disk I/O error 
+** has ever happened.
+*/
+DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
+  PgHdr *pPg;
+
+  assert( pPager!=0 );
+  assert( pgno!=0 );
+
+  if( pPager->state==PAGER_UNLOCK ){
+    assert( !pPager->pAll || pPager->exclusiveMode );
+    return 0;
+  }
+  if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
+    return 0;
+  }
+  pPg = pager_lookup(pPager, pgno);
+  if( pPg==0 ) return 0;
+  page_ref(pPg);
+  return pPg;
+}
+
+/*
+** Release a page.
+**
+** If the number of references to the page drop to zero, then the
+** page is added to the LRU list.  When all references to all pages
+** are released, a rollback occurs and the lock on the database is
+** removed.
+*/
+int sqlite3PagerUnref(DbPage *pPg){
+
+  /* Decrement the reference count for this page
+  */
+  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(pPg, 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 && (!pPager->exclusiveMode || pPager->journalOff>0) ){
+      pagerUnlockAndRollback(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 );
+  sqlite3PagerPagecount(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);
+  assert( rc!=SQLITE_OK || pPager->jfd );
+  pPager->journalOff = 0;
+  pPager->setMaster = 0;
+  pPager->journalHdr = 0;
+  if( rc!=SQLITE_OK ){
+    if( rc==SQLITE_NOMEM ){
+      sqlite3OsDelete(pPager->zJournal);
+    }
+    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 = sqlite3PagerStmtBegin(pPager);
+  }
+  if( rc!=SQLITE_OK && rc!=SQLITE_NOMEM ){
+    rc = pager_end_transaction(pPager);
+    if( rc==SQLITE_OK ){
+      rc = SQLITE_FULL;
+    }
+  }
+  return rc;
+
+failed_to_open_journal:
+  sqliteFree(pPager->aInJournal);
+  pPager->aInJournal = 0;
+  return rc;
+}
+
+/*
+** Acquire a write-lock on the database.  The lock is removed when
+** the any of the following happen:
+**
+**   *  sqlite3PagerCommitPhaseTwo() is called.
+**   *  sqlite3PagerRollback() is called.
+**   *  sqlite3PagerClose() is called.
+**   *  sqlite3PagerUnref() is called to on every outstanding page.
+**
+** The first parameter to this routine is a pointer to any open page of the
+** database file.  Nothing changes about the page - it is used merely to
+** acquire a pointer to the Pager structure and as proof that there is
+** already a read-lock on the database.
+**
+** The second parameter indicates how much space in bytes to reserve for a
+** master journal file-name at the start of the journal when it is created.
+**
+** A journal file is opened if this is not a temporary file.  For temporary
+** files, the opening of the journal file is deferred until there is an
+** actual need to write to the journal.
+**
+** If the database is already reserved for writing, this routine is a no-op.
+**
+** If exFlag is true, go ahead and get an EXCLUSIVE lock on the file
+** immediately instead of waiting until we try to flush the cache.  The
+** exFlag is ignored if a transaction is already active.
+*/
+int sqlite3PagerBegin(DbPage *pPg, int exFlag){
+  Pager *pPager = pPg->pPager;
+  int rc = SQLITE_OK;
+  assert( pPg->nRef>0 );
+  assert( pPager->state!=PAGER_UNLOCK );
+  if( pPager->state==PAGER_SHARED ){
+    assert( pPager->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;
+      PAGERTRACE2("TRANSACTION %d\n", PAGERID(pPager));
+      if( pPager->useJournal && !pPager->tempFile ){
+        rc = pager_open_journal(pPager);
+      }
+    }
+  }else if( pPager->journalOpen && pPager->journalOff==0 ){
+    /* This happens when the pager was in exclusive-access mode last
+    ** time a (read or write) transaction was successfully concluded
+    ** by this connection. Instead of deleting the journal file it was 
+    ** kept open and truncated to 0 bytes.
+    */
+    assert( pPager->nRec==0 );
+    assert( pPager->origDbSize==0 );
+    assert( pPager->aInJournal==0 );
+    sqlite3PagerPagecount(pPager);
+    pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
+    if( !pPager->aInJournal ){
+      rc = SQLITE_NOMEM;
+    }else{
+      pPager->origDbSize = pPager->dbSize;
+      rc = writeJournalHdr(pPager);
+    }
+  }
+  assert( !pPager->journalOpen || pPager->journalOff>0 || rc!=SQLITE_OK );
+  return rc;
+}
+
+/*
+** Make a page dirty.  Set its dirty flag and add it to the dirty
+** page list.
+*/
+static void makeDirty(PgHdr *pPg){
+  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 sqlite3PagerCommit() or sqlite3PagerRollback() to
+** reset.
+*/
+static int pager_write(PgHdr *pPg){
+  void *pData = PGHDR_TO_DATA(pPg);
+  Pager *pPager = pPg->pPager;
+  int rc = SQLITE_OK;
+
+  /* Check for errors
+  */
+  if( pPager->errCode ){ 
+    return pPager->errCode;
+  }
+  if( pPager->readOnly ){
+    return SQLITE_PERM;
+  }
+
+  assert( !pPager->setMaster );
+
+  CHECK_PAGE(pPg);
+
+  /* If this page was previously acquired with noContent==1, that means
+  ** we didn't really read in the content of the page.  This can happen
+  ** (for example) when the page is being moved to the freelist.  But
+  ** now we are (perhaps) moving the page off of the freelist for
+  ** reuse and we need to know its original content so that content
+  ** can be stored in the rollback journal.  So do the read at this
+  ** time.
+  */
+  rc = pager_get_content(pPg);
+  if( rc ){
+    return rc;
+  }
+
+  /* Mark the page as dirty.  If the page has already been written
+  ** to the journal then we can return right away.
+  */
+  makeDirty(pPg);
+  if( pPg->inJournal && (pageInStatement(pPg) || 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 = sqlite3PagerBegin(pPg, 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);
+          PAGERTRACE3("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);
+          IOTRACE(("JOUT %p %d %lld %d\n", pPager, pPg->pgno,
+                   pPager->journalOff, szPg));
+          PAGER_INCR(sqlite3_pager_writej_count);
+          pPager->journalOff += szPg;
+          PAGERTRACE5("JOURNAL %d page %d needSync=%d hash(%08x)\n",
+               PAGERID(pPager), pPg->pgno, pPg->needSync, pager_pagehash(pPg));
+          *(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);
+          }
+        }
+      }else{
+        pPg->needSync = !pPager->journalStarted && !pPager->noSync;
+        PAGERTRACE4("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 
+     && !pageInStatement(pPg) 
+     && (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);
+        }
+        PAGERTRACE3("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno);
+        page_add_to_stmt_list(pPg);
+      }else{
+        char *pData2 = CODEC2(pPager, pData, pPg->pgno, 7)-4;
+        put32bits(pData2, pPg->pgno);
+        rc = sqlite3OsWrite(pPager->stfd, pData2, pPager->pageSize+4);
+        PAGERTRACE3("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);
+      }
+    }
+  }
+
+  /* Update the database size and return.
+  */
+  assert( pPager->state>=PAGER_SHARED );
+  if( pPager->dbSize<(int)pPg->pgno ){
+    pPager->dbSize = pPg->pgno;
+    if( !MEMDB && pPager->dbSize==PENDING_BYTE/pPager->pageSize ){
+      pPager->dbSize++;
+    }
+  }
+  return rc;
+}
+
+/*
+** This function is used to mark a data-page as writable. It uses 
+** pager_write() to open a journal file (if it is not already open)
+** and write the page *pData to the journal.
+**
+** The difference between this function and pager_write() is that this
+** function also deals with the special case where 2 or more pages
+** fit on a single disk sector. In this case all co-resident pages
+** must have been written to the journal file before returning.
+*/
+int sqlite3PagerWrite(DbPage *pDbPage){
+  int rc = SQLITE_OK;
+
+  PgHdr *pPg = pDbPage;
+  Pager *pPager = pPg->pPager;
+  Pgno nPagePerSector = (pPager->sectorSize/pPager->pageSize);
+
+  if( !MEMDB && nPagePerSector>1 ){
+    Pgno nPageCount;          /* Total number of pages in database file */
+    Pgno pg1;                 /* First page of the sector pPg is located on. */
+    int nPage;                /* Number of pages starting at pg1 to journal */
+    int ii;
+
+    /* Set the doNotSync flag to 1. This is because we cannot allow a journal
+    ** header to be written between the pages journaled by this function.
+    */
+    assert( pPager->doNotSync==0 );
+    pPager->doNotSync = 1;
+
+    /* This trick assumes that both the page-size and sector-size are
+    ** an integer power of 2. It sets variable pg1 to the identifier
+    ** of the first page of the sector pPg is located on.
+    */
+    pg1 = ((pPg->pgno-1) & ~(nPagePerSector-1)) + 1;
+
+    nPageCount = sqlite3PagerPagecount(pPager);
+    if( pPg->pgno>nPageCount ){
+      nPage = (pPg->pgno - pg1)+1;
+    }else if( (pg1+nPagePerSector-1)>nPageCount ){
+      nPage = nPageCount+1-pg1;
+    }else{
+      nPage = nPagePerSector;
+    }
+    assert(nPage>0);
+    assert(pg1<=pPg->pgno);
+    assert((pg1+nPage)>pPg->pgno);
+
+    for(ii=0; ii<nPage && rc==SQLITE_OK; ii++){
+      Pgno pg = pg1+ii;
+      if( !pPager->aInJournal || pg==pPg->pgno || 
+          pg>pPager->origDbSize || !(pPager->aInJournal[pg/8]&(1<<(pg&7)))
+      ) {
+        if( pg!=PAGER_MJ_PGNO(pPager) ){
+          PgHdr *pPage;
+          rc = sqlite3PagerGet(pPager, pg, &pPage);
+          if( rc==SQLITE_OK ){
+            rc = pager_write(pPage);
+            sqlite3PagerUnref(pPage);
+          }
+        }
+      }
+    }
+
+    assert( pPager->doNotSync==1 );
+    pPager->doNotSync = 0;
+  }else{
+    rc = pager_write(pDbPage);
+  }
+  return rc;
+}
+
+/*
+** Return TRUE if the page given in the argument was previously passed
+** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
+** to change the content of the page.
+*/
+#ifndef NDEBUG
+int sqlite3PagerIswriteable(DbPage *pPg){
+  return pPg->dirty;
+}
+#endif
+
+#ifndef SQLITE_OMIT_VACUUM
+/*
+** Replace the content of a single page with the information in the third
+** argument.
+*/
+int sqlite3PagerOverwrite(Pager *pPager, Pgno pgno, void *pData){
+  PgHdr *pPg;
+  int rc;
+
+  rc = sqlite3PagerGet(pPager, pgno, &pPg);
+  if( rc==SQLITE_OK ){
+    rc = sqlite3PagerWrite(pPg);
+    if( rc==SQLITE_OK ){
+      memcpy(sqlite3PagerGetData(pPg), pData, pPager->pageSize);
+    }
+    sqlite3PagerUnref(pPg);
+  }
+  return rc;
+}
+#endif
+
+/*
+** A call to this routine tells the pager that it is not necessary to
+** write the information on page pPg back to the disk, even though
+** that page might be marked as dirty.
+**
+** The overlying software layer calls this routine when all of the data
+** on the given page is unused.  The pager marks the page as clean so
+** that it does not get written to disk.
+**
+** Tests show that this optimization, together with the
+** sqlite3PagerDontRollback() below, more than double the speed
+** of large INSERT operations and quadruple the speed of large DELETEs.
+**
+** When this routine is called, set the alwaysRollback flag to true.
+** Subsequent calls to sqlite3PagerDontRollback() for the same page
+** will thereafter be ignored.  This is necessary to avoid a problem
+** where a page with data is added to the freelist during one part of
+** a transaction then removed from the freelist during a later part
+** of the same transaction and reused for some other purpose.  When it
+** is first added to the freelist, this routine is called.  When reused,
+** the sqlite3PagerDontRollback() routine is called.  But because the
+** page contains critical data, we still need to be sure it gets
+** rolled back in spite of the sqlite3PagerDontRollback() call.
+*/
+void sqlite3PagerDontWrite(DbPage *pDbPage){
+  PgHdr *pPg = pDbPage;
+  Pager *pPager = pPg->pPager;
+
+  if( MEMDB ) return;
+  pPg->alwaysRollback = 1;
+  if( pPg->dirty && !pPager->stmtInUse ){
+    assert( pPager->state>=PAGER_SHARED );
+    if( pPager->dbSize==(int)pPg->pgno && pPager->origDbSize<pPager->dbSize ){
+      /* If this pages is the last page in the file and the file has grown
+      ** during the current transaction, then do NOT mark the page as clean.
+      ** When the database file grows, we must make sure that the last page
+      ** gets written at least once so that the disk file will be the correct
+      ** size. If you do not write this page and the size of the file
+      ** on the disk ends up being too small, that can lead to database
+      ** corruption during the next transaction.
+      */
+    }else{
+      PAGERTRACE3("DONT_WRITE page %d of %d\n", pPg->pgno, PAGERID(pPager));
+      IOTRACE(("CLEAN %p %d\n", pPager, pPg->pgno))
+      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.
+**
+** If we have not yet actually read the content of this page (if
+** the PgHdr.needRead flag is set) then this routine acts as a promise
+** that we will never need to read the page content in the future.
+** so the needRead flag can be cleared at this point.
+*/
+void sqlite3PagerDontRollback(DbPage *pPg){
+  Pager *pPager = pPg->pPager;
+
+  assert( pPager->state>=PAGER_RESERVED );
+  if( 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;
+    pPg->needRead = 0;
+    if( pPager->stmtInUse ){
+      pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
+    }
+    PAGERTRACE3("DONT_ROLLBACK page %d of %d\n", pPg->pgno, PAGERID(pPager));
+    IOTRACE(("GARBAGE %p %d\n", pPager, pPg->pgno))
+  }
+  if( pPager->stmtInUse 
+   && !pageInStatement(pPg) 
+   && (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);
+  }
+}
+
+
+/*
+** 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){
+  PgHdr *pPgHdr;
+  u32 change_counter;
+  int rc;
+
+  if( !pPager->changeCountDone ){
+    /* Open page 1 of the file for writing. */
+    rc = sqlite3PagerGet(pPager, 1, &pPgHdr);
+    if( rc!=SQLITE_OK ) return rc;
+    rc = sqlite3PagerWrite(pPgHdr);
+    if( rc!=SQLITE_OK ) return rc;
+  
+    /* Increment the value just read and write it back to byte 24. */
+    change_counter = sqlite3Get4byte((u8*)pPager->dbFileVers);
+    change_counter++;
+    put32bits(((char*)PGHDR_TO_DATA(pPgHdr))+24, change_counter);
+    /* Release the page reference. */
+    sqlite3PagerUnref(pPgHdr);
+    pPager->changeCountDone = 1;
+  }
+  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 sqlite3PagerCommitPhaseOne() call.
+**
+** If parameter nTrunc is non-zero, then the pager file is truncated to
+** nTrunc pages (this is used by auto-vacuum databases).
+*/
+int sqlite3PagerCommitPhaseOne(Pager *pPager, const char *zMaster, Pgno nTrunc){
+  int rc = SQLITE_OK;
+
+  PAGERTRACE4("DATABASE SYNC: File=%s zMaster=%s nTrunc=%d\n", 
+      pPager->zFilename, zMaster, nTrunc);
+
+  /* If this is an in-memory db, or no pages have been written to, or this
+  ** function has already been called, it is a no-op.
+  */
+  if( pPager->state!=PAGER_SYNCED && !MEMDB && pPager->dirtyCache ){
+    PgHdr *pPg;
+    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;
+        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 = sqlite3PagerGet(pPager, i, &pPg);
+            if( rc!=SQLITE_OK ) goto sync_exit;
+            rc = sqlite3PagerWrite(pPg);
+            sqlite3PagerUnref(pPg);
+            if( rc!=SQLITE_OK ) goto sync_exit;
+          }
+        } 
+      }
+#endif
+      rc = writeMasterJournal(pPager, zMaster);
+      if( rc!=SQLITE_OK ) goto sync_exit;
+      rc = syncJournal(pPager);
+      if( rc!=SQLITE_OK ) goto sync_exit;
+    }
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+    if( nTrunc!=0 ){
+      rc = sqlite3PagerTruncate(pPager, nTrunc);
+      if( rc!=SQLITE_OK ) goto sync_exit;
+    }
+#endif
+
+    /* Write all dirty pages to the database file */
+    pPg = pager_get_all_dirty_pages(pPager);
+    rc = pager_write_pagelist(pPg);
+    if( rc!=SQLITE_OK ) goto sync_exit;
+    pPager->pDirty = 0;
+
+    /* Sync the database file. */
+    if( !pPager->noSync ){
+      rc = sqlite3OsSync(pPager->fd, 0);
+    }
+    IOTRACE(("DBSYNC %p\n", pPager))
+
+    pPager->state = PAGER_SYNCED;
+  }else if( MEMDB && nTrunc!=0 ){
+    rc = sqlite3PagerTruncate(pPager, nTrunc);
+  }
+
+sync_exit:
+  if( rc==SQLITE_IOERR_BLOCKED ){
+    /* pager_incr_changecounter() may attempt to obtain an exclusive
+     * lock to spill the cache and return IOERR_BLOCKED. But since 
+     * there is no chance the cache is inconsistent, it's
+     * better to return SQLITE_BUSY.
+     */
+    rc = SQLITE_BUSY;
+  }
+  return rc;
+}
+
+
+/*
+** Commit all changes to the database and release the write lock.
+**
+** If the commit fails for any reason, a rollback attempt is made
+** and an error code is returned.  If the commit worked, SQLITE_OK
+** is returned.
+*/
+int sqlite3PagerCommitPhaseTwo(Pager *pPager){
+  int rc;
+  PgHdr *pPg;
+
+  if( pPager->errCode ){
+    return pPager->errCode;
+  }
+  if( pPager->state<PAGER_RESERVED ){
+    return SQLITE_ERROR;
+  }
+  PAGERTRACE2("COMMIT %d\n", PAGERID(pPager));
+  if( MEMDB ){
+    pPg = pager_get_all_dirty_pages(pPager);
+    while( pPg ){
+      PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+      clearHistory(pHist);
+      pPg->dirty = 0;
+      pPg->inJournal = 0;
+      pHist->inStmt = 0;
+      pPg->needSync = 0;
+      pHist->pPrevStmt = pHist->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;
+  }
+  assert( pPager->journalOpen || !pPager->dirtyCache );
+  assert( pPager->state==PAGER_SYNCED || !pPager->dirtyCache );
+  rc = pager_end_transaction(pPager);
+  return pager_error(pPager, rc);
+}
+
+/*
+** Rollback all changes.  The database falls back to PAGER_SHARED mode.
+** All in-memory cache pages revert to their original data contents.
+** The journal is deleted.
+**
+** This routine cannot fail unless some other process is not following
+** the correct locking protocol or unless some other
+** process is writing trash into the journal file (SQLITE_CORRUPT) or
+** unless a prior malloc() failed (SQLITE_NOMEM).  Appropriate error
+** codes are returned for all these occasions.  Otherwise,
+** SQLITE_OK is returned.
+*/
+int sqlite3PagerRollback(Pager *pPager){
+  int rc;
+  PAGERTRACE2("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);
+        PAGERTRACE3("ROLLBACK-PAGE %d of %d\n", p->pgno, PAGERID(pPager));
+      }else{
+        PAGERTRACE3("PAGE %d is clean on %d\n", p->pgno, PAGERID(pPager));
+      }
+      clearHistory(pHist);
+      p->dirty = 0;
+      p->inJournal = 0;
+      pHist->inStmt = 0;
+      pHist->pPrevStmt = pHist->pNextStmt = 0;
+      if( pPager->xReiniter ){
+        pPager->xReiniter(p, pPager->pageSize);
+      }
+    }
+    pPager->pDirty = 0;
+    pPager->pStmt = 0;
+    pPager->dbSize = pPager->origDbSize;
+    pager_truncate_cache(pPager);
+    pPager->stmtInUse = 0;
+    pPager->state = PAGER_SHARED;
+    return SQLITE_OK;
+  }
+
+  if( !pPager->dirtyCache || !pPager->journalOpen ){
+    rc = pager_end_transaction(pPager);
+    return rc;
+  }
+
+  if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
+    if( pPager->state>=PAGER_EXCLUSIVE ){
+      pager_playback(pPager, 0);
+    }
+    return pPager->errCode;
+  }
+  if( pPager->state==PAGER_RESERVED ){
+    int rc2;
+    rc = pager_playback(pPager, 0);
+    rc2 = pager_end_transaction(pPager);
+    if( rc==SQLITE_OK ){
+      rc = rc2;
+    }
+  }else{
+    rc = pager_playback(pPager, 0);
+  }
+  /* pager_reset(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 sqlite3PagerIsreadonly(Pager *pPager){
+  return pPager->readOnly;
+}
+
+/*
+** Return the number of references to the pager.
+*/
+int sqlite3PagerRefcount(Pager *pPager){
+  return pPager->nRef;
+}
+
+#ifdef SQLITE_TEST
+/*
+** This routine is used for testing and analysis only.
+*/
+int *sqlite3PagerStats(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] = 0;  /* Used to be 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 sqlite3PagerStmtBegin(Pager *pPager){
+  int rc;
+  assert( !pPager->stmtInUse );
+  assert( pPager->state>=PAGER_SHARED );
+  assert( pPager->dbSize>=0 );
+  PAGERTRACE2("STMT-BEGIN %d\n", PAGERID(pPager));
+  if( MEMDB ){
+    pPager->stmtInUse = 1;
+    pPager->stmtSize = pPager->dbSize;
+    return SQLITE_OK;
+  }
+  if( !pPager->journalOpen ){
+    pPager->stmtAutoopen = 1;
+    return SQLITE_OK;
+  }
+  assert( pPager->journalOpen );
+  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 = sqlite3PagerOpentemp(&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 sqlite3PagerStmtCommit(Pager *pPager){
+  if( pPager->stmtInUse ){
+    PgHdr *pPg, *pNext;
+    PAGERTRACE2("STMT-COMMIT %d\n", PAGERID(pPager));
+    if( !MEMDB ){
+      sqlite3OsSeek(pPager->stfd, 0);
+      /* sqlite3OsTruncate(pPager->stfd, 0); */
+      sqliteFree( pPager->aInStmt );
+      pPager->aInStmt = 0;
+    }else{
+      for(pPg=pPager->pStmt; pPg; pPg=pNext){
+        PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
+        pNext = pHist->pNextStmt;
+        assert( pHist->inStmt );
+        pHist->inStmt = 0;
+        pHist->pPrevStmt = pHist->pNextStmt = 0;
+        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 sqlite3PagerStmtRollback(Pager *pPager){
+  int rc;
+  if( pPager->stmtInUse ){
+    PAGERTRACE2("STMT-ROLLBACK %d\n", PAGERID(pPager));
+    if( MEMDB ){
+      PgHdr *pPg;
+      PgHistory *pHist;
+      for(pPg=pPager->pStmt; pPg; pPg=pHist->pNextStmt){
+        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;
+      pager_truncate_cache(pPager);
+      rc = SQLITE_OK;
+    }else{
+      rc = pager_stmt_playback(pPager);
+    }
+    sqlite3PagerStmtCommit(pPager);
+  }else{
+    rc = SQLITE_OK;
+  }
+  pPager->stmtAutoopen = 0;
+  return rc;
+}
+
+/*
+** Return the full pathname of the database file.
+*/
+const char *sqlite3PagerFilename(Pager *pPager){
+  return pPager->zFilename;
+}
+
+/*
+** Return the directory of the database file.
+*/
+const char *sqlite3PagerDirname(Pager *pPager){
+  return pPager->zDirectory;
+}
+
+/*
+** Return the full pathname of the journal file.
+*/
+const char *sqlite3PagerJournalname(Pager *pPager){
+  return pPager->zJournal;
+}
+
+/*
+** Return true if fsync() calls are disabled for this pager.  Return FALSE
+** if fsync()s are executed normally.
+*/
+int sqlite3PagerNosync(Pager *pPager){
+  return pPager->noSync;
+}
+
+#ifdef SQLITE_HAS_CODEC
+/*
+** Set the codec for this pager
+*/
+void sqlite3PagerSetCodec(
+  Pager *pPager,
+  void *(*xCodec)(void*,void*,Pgno,int),
+  void *pCodecArg
+){
+  pPager->xCodec = xCodec;
+  pPager->pCodecArg = pCodecArg;
+}
+#endif
+
+#ifndef SQLITE_OMIT_AUTOVACUUM
+/*
+** Move the page pPg to location pgno in the file. 
+**
+** There must be no references to the page previously located at
+** pgno (which we call pPgOld) though that page is allowed to be
+** in cache.  If the page previous located at pgno is not already
+** in the rollback journal, it is not put there by by this routine.
+**
+** References to the page pPg remain valid. Updating any
+** meta-data associated with pPg (i.e. data stored in the nExtra bytes
+** allocated along with the page) is the responsibility of the caller.
+**
+** A transaction must be active when this routine is called. It used to be
+** required that a statement transaction was not active, but this restriction
+** has been removed (CREATE INDEX needs to move a page when a statement
+** transaction is active).
+*/
+int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno){
+  PgHdr *pPgOld;  /* The page being overwritten. */
+  int h;
+  Pgno needSyncPgno = 0;
+
+  assert( pPg->nRef>0 );
+
+  PAGERTRACE5("MOVE %d page %d (needSync=%d) moves to %d\n", 
+      PAGERID(pPager), pPg->pgno, pPg->needSync, pgno);
+  IOTRACE(("MOVE %p %d %d\n", pPager, pPg->pgno, pgno))
+
+  pager_get_content(pPg);
+  if( pPg->needSync ){
+    needSyncPgno = pPg->pgno;
+    assert( pPg->inJournal || (int)pgno>pPager->origDbSize );
+    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.
+  */
+  pPg->needSync = 0;
+  pPgOld = pager_lookup(pPager, pgno);
+  if( pPgOld ){
+    assert( pPgOld->nRef==0 );
+    unlinkHashChain(pPager, pPgOld);
+    makeClean(pPgOld);
+    pPg->needSync = pPgOld->needSync;
+  }else{
+    pPg->needSync = 0;
+  }
+  if( pPager->aInJournal && (int)pgno<=pPager->origDbSize ){
+    pPg->inJournal =  (pPager->aInJournal[pgno/8] & (1<<(pgno&7)))!=0;
+  }else{
+    pPg->inJournal = 0;
+    assert( pPg->needSync==0 || (int)pgno>pPager->origDbSize );
+  }
+
+  /* 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 sqlite3PagerGet() call may cause the journal to sync. So make
+    ** sure the Pager.needSync flag is set too.
+    */
+    int rc;
+    PgHdr *pPgHdr;
+    assert( pPager->needSync );
+    rc = sqlite3PagerGet(pPager, needSyncPgno, &pPgHdr);
+    if( rc!=SQLITE_OK ) return rc;
+    pPager->needSync = 1;
+    pPgHdr->needSync = 1;
+    pPgHdr->inJournal = 1;
+    makeDirty(pPgHdr);
+    sqlite3PagerUnref(pPgHdr);
+  }
+
+  return SQLITE_OK;
+}
+#endif
+
+/**
+** Addition: This will attempt to populate the database cache with
+** the first N bytes of the file, where N is the total size of the cache.
+** Because we can load this as one chunk from the disk, this is much faster
+** than loading a subset of the pages one at a time in random order.
+**
+** The pager must be initialized before this function is called. This means a
+** statement must be open that has initialized the pager and is keeping the
+** cache in memory.
+**/
+int sqlite3PagerLoadall(Pager* pPager)
+{
+  int i;
+  int rc;
+  int loadSize;
+  int loadPages;
+  unsigned char *fileData;
+
+  if (pPager->dbSize < 0 || pPager->pageSize < 0) {
+    /* pager not initialized, this means a statement is not open */
+    return SQLITE_MISUSE;
+  }
+
+  /* compute sizes */
+  if (pPager->mxPage < pPager->dbSize)
+    loadPages = pPager->mxPage;
+  else
+    loadPages = pPager->dbSize;
+  loadSize = loadPages * pPager->pageSize;
+
+  rc = sqlite3OsSeek(pPager->fd, 0);
+  if (rc != SQLITE_OK)
+    return rc;
+
+  /* load the file as one chunk */
+  fileData = sqliteMallocRaw(loadSize);
+  if (! fileData)
+    return SQLITE_NOMEM;
+  rc = sqlite3OsRead(pPager->fd, fileData, loadSize);
+  if (rc != SQLITE_OK) {
+    sqliteFree(fileData);
+    return rc;
+  }
+
+  /* Copy the data to each page. Note that the page numbers we pass to _get
+   * are one-based, 0 is a marker for no page. We also need to check that we
+   * haven't loaded more pages than the cache can hold total. There may have
+   * already been a few pages loaded before, so we may fill the cache before
+   * loading all of the pages we want to.
+   */
+  for(i=1; i <= loadPages && pPager->nPage < pPager->mxPage; i++) {
+    DbPage *pPage;
+    rc = sqlite3PagerAcquire2(pPager, i, &pPage, 0,
+                              &fileData[(i-1)*(i64)pPager->pageSize]);
+    if (rc != SQLITE_OK)
+      break;
+    sqlite3PagerUnref(pPage);
+  }
+  sqliteFree(fileData);
+  return SQLITE_OK;
+}
+
+/*
+** Return a pointer to the data for the specified page.
+*/
+void *sqlite3PagerGetData(DbPage *pPg){
+  return PGHDR_TO_DATA(pPg);
+}
+
+/*
+** Return a pointer to the Pager.nExtra bytes of "extra" space 
+** allocated along with the specified page.
+*/
+void *sqlite3PagerGetExtra(DbPage *pPg){
+  Pager *pPager = pPg->pPager;
+  return (pPager?PGHDR_TO_EXTRA(pPg, pPager):0);
+}
+
+/*
+** Get/set the locking-mode for this pager. Parameter eMode must be one
+** of PAGER_LOCKINGMODE_QUERY, PAGER_LOCKINGMODE_NORMAL or 
+** PAGER_LOCKINGMODE_EXCLUSIVE. If the parameter is not _QUERY, then
+** the locking-mode is set to the value specified.
+**
+** The returned value is either PAGER_LOCKINGMODE_NORMAL or
+** PAGER_LOCKINGMODE_EXCLUSIVE, indicating the current (possibly updated)
+** locking-mode.
+*/
+int sqlite3PagerLockingMode(Pager *pPager, int eMode){
+  assert( eMode==PAGER_LOCKINGMODE_QUERY
+            || eMode==PAGER_LOCKINGMODE_NORMAL
+            || eMode==PAGER_LOCKINGMODE_EXCLUSIVE );
+  assert( PAGER_LOCKINGMODE_QUERY<0 );
+  assert( PAGER_LOCKINGMODE_NORMAL>=0 && PAGER_LOCKINGMODE_EXCLUSIVE>=0 );
+  if( eMode>=0 && !pPager->tempFile ){
+    pPager->exclusiveMode = eMode;
+  }
+  return (int)pPager->exclusiveMode;
+}
+
+#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 sqlite3PagerLockstate(Pager *pPager){
+  return sqlite3OsLockState(pPager->fd);
+}
+#endif
+
+#ifdef SQLITE_DEBUG
+/*
+** Print a listing of all referenced pages and their ref count.
+*/
+void sqlite3PagerRefdump(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 */