** 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 1.106 2004/05/10 10:34:49 danielk1977 Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
** 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 */
  int nRef;                      /* Number of users of this page */
  PgHdr *pNextFree, *pPrevFree;  /* Freelist of pages where nRef==0 */
  PgHdr *pNextAll, *pPrevAll;    /* A list of all pages */
  PgHdr *pNextCkpt, *pPrevCkpt;  /* List of pages in the checkpoint journal */

  u8 inJournal;                  /* TRUE if has been written to journal */
  u8 inCkpt;                     /* TRUE if written to the checkpoint journal */
  u8 dirty;                      /* TRUE if we need to write back changes */
  u8 needSync;                   /* Sync journal before writing this page */
  u8 alwaysRollback;             /* Disable dont_rollback() for this page */

  PgHdr *pDirty;                 /* Dirty pages sorted by PgHdr.pgno */
  /* SQLITE_PAGE_SIZE bytes of page data follow this header */
  /* Pager.nExtra bytes of local data follow the page data */
};


















/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC(P,D,N,X) if( P->xCodec ){ P->xCodec(P->pCodecArg,D,N,X); }
#else
................................................................................
/*
** 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(P) ((void*)&((char*)(&(P)[1]))[SQLITE_PAGE_SIZE])



/*
** How big to make the hash table used for locating in-memory pages
** by page number.
*/
#define N_PG_HASH 2048

................................................................................
** A open page cache is an instance of the following structure.
*/
struct Pager {
  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 cpfd;                /* File descriptor for the checkpoint journal */
  int dbSize;                 /* Number of pages in the file */
  int origDbSize;             /* dbSize before the current change */
  int ckptSize;               /* Size of database (in pages) at ckpt_begin() */
  off_t ckptJSize;            /* Size of journal at ckpt_begin() */
  int nRec;                   /* Number of pages written to the journal */
  u32 cksumInit;              /* Quasi-random value added to every checksum */
  int ckptNRec;               /* Number of records in the checkpoint journal */
  int nExtra;                 /* Add this many bytes to each in-memory page */
  void (*xDestructor)(void*); /* Call this routine when freeing pages */
  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 */
  int nHit, nMiss, nOvfl;     /* Cache hits, missing, and LRU overflows */
  void (*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
  void *pCodecArg;            /* First argument to xCodec() */

  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 ckptOpen;                /* True if the checkpoint journal is open */
  u8 ckptInUse;               /* True we are in a checkpoint */
  u8 ckptAutoopen;            /* Open ckpt 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 state;                   /* SQLITE_UNLOCK, _READLOCK or _WRITELOCK */
  u8 errMask;                 /* One of several kinds of errors */
  u8 tempFile;                /* zFilename is a temporary file */
  u8 readOnly;                /* True for a read-only database */
  u8 needSync;                /* True if an fsync() is needed on the journal */
  u8 dirtyFile;               /* True if database file has changed in any way */
  u8 alwaysRollback;          /* Disable dont_rollback() for all pages */

  u8 *aInJournal;             /* One bit for each page in the database file */
  u8 *aInCkpt;                /* One bit for each page in the database */
  PgHdr *pFirst, *pLast;      /* List of free pages */
  PgHdr *pFirstSynced;        /* First free page with PgHdr.needSync==0 */
  PgHdr *pAll;                /* List of all pages */
  PgHdr *pCkpt;               /* List of pages in the checkpoint journal */
  PgHdr *aHash[N_PG_HASH];    /* Hash table to map page number of PgHdr */
};

/*
** These are bits that can be set in Pager.errMask.
*/
#define PAGER_ERR_FULL     0x01  /* a write() failed */
................................................................................
/*
** The following integer determines what format to use when creating
** new primary journal files.  By default we always use format 3.
** When testing, we can set this value to older journal formats in order to
** make sure that newer versions of the library are able to rollback older
** journal files.
**
** Note that checkpoint journals always use format 2 and omit the header.
*/
#ifdef SQLITE_TEST
int journal_format = 3;
#else
# define journal_format 3
#endif

................................................................................
  if( pPager->errMask & PAGER_ERR_MEM )     rc = SQLITE_NOMEM;
  if( pPager->errMask & PAGER_ERR_CORRUPT ) rc = SQLITE_CORRUPT;
  return rc;
}

/*
** Add or remove a page from the list of all pages that are in the
** checkpoint journal.
**
** The Pager keeps a separate list of pages that are currently in
** the checkpoint journal.  This helps the sqlite3pager_stmt_commit()
** routine run MUCH faster for the common case where there are many
** pages in memory but only a few are in the checkpoint journal.
*/
static void page_add_to_stmt_list(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  if( pPg->inCkpt ) return;
  assert( pPg->pPrevCkpt==0 && pPg->pNextCkpt==0 );
  pPg->pPrevCkpt = 0;
  if( pPager->pCkpt ){
    pPager->pCkpt->pPrevCkpt = pPg;
  }
  pPg->pNextCkpt = pPager->pCkpt;
  pPager->pCkpt = pPg;
  pPg->inCkpt = 1;
}
static void page_remove_from_stmt_list(PgHdr *pPg){
  if( !pPg->inCkpt ) return;
  if( pPg->pPrevCkpt ){
    assert( pPg->pPrevCkpt->pNextCkpt==pPg );
    pPg->pPrevCkpt->pNextCkpt = pPg->pNextCkpt;
  }else{
    assert( pPg->pPager->pCkpt==pPg );
    pPg->pPager->pCkpt = pPg->pNextCkpt;
  }
  if( pPg->pNextCkpt ){
    assert( pPg->pNextCkpt->pPrevCkpt==pPg );
    pPg->pNextCkpt->pPrevCkpt = pPg->pPrevCkpt;
  }
  pPg->pNextCkpt = 0;
  pPg->pPrevCkpt = 0;
  pPg->inCkpt = 0;
}

/*
** Find a page in the hash table given its page number.  Return
** a pointer to the page or NULL if not found.
*/
static PgHdr *pager_lookup(Pager *pPager, Pgno pgno){
................................................................................
** a file is an expensive operation.
*/
static int pager_unwritelock(Pager *pPager){
  int rc;
  PgHdr *pPg;
  if( pPager->state<SQLITE_WRITELOCK ) return SQLITE_OK;
  sqlite3pager_stmt_commit(pPager);
  if( pPager->ckptOpen ){
    sqlite3OsClose(&pPager->cpfd);
    pPager->ckptOpen = 0;
  }
  if( pPager->journalOpen ){
    sqlite3OsClose(&pPager->jfd);
    pPager->journalOpen = 0;
    sqlite3OsDelete(pPager->zJournal);
    sqliteFree( pPager->aInJournal );
    pPager->aInJournal = 0;
................................................................................
  }else{
    rc = pager_unwritelock(pPager);
  }
  return rc;
}

/*
** Playback the checkpoint 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 checkpoint is stored in pPager->ckptSize, not in the
**         journal file itself.
**
**    (2)  In addition to playing back the checkpoint journal, also
**         playback all pages of the transaction journal beginning
**         at offset pPager->ckptJSize.
*/
static int pager_stmt_playback(Pager *pPager){
  off_t szJ;               /* Size of the full journal */
  int nRec;                /* Number of Records */
  int i;                   /* Loop counter */
  int rc;

  /* Truncate the database back to its original size.
  */
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)pPager->ckptSize);
  pPager->dbSize = pPager->ckptSize;

  /* Figure out how many records are in the checkpoint journal.
  */
  assert( pPager->ckptInUse && pPager->journalOpen );
  sqlite3OsSeek(&pPager->cpfd, 0);
  nRec = pPager->ckptNRec;
  
  /* Copy original pages out of the checkpoint journal and back into the
  ** database file.  Note that the checkpoint journal always uses format
  ** 2 instead of format 3 since it does not need to be concerned with
  ** power failures corrupting the journal and can thus omit the checksums.
  */
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->cpfd, 2);
    assert( rc!=SQLITE_DONE );
    if( rc!=SQLITE_OK ) goto end_stmt_playback;
  }

  /* Figure out how many pages need to be copied out of the transaction
  ** journal.
  */
  rc = sqlite3OsSeek(&pPager->jfd, pPager->ckptJSize);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  rc = sqlite3OsFileSize(&pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  nRec = (szJ - pPager->ckptJSize)/JOURNAL_PG_SZ(journal_format);
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->jfd, journal_format);
    if( rc!=SQLITE_OK ){
      assert( rc!=SQLITE_DONE );
      goto end_stmt_playback;
    }
  }
................................................................................
){
  Pager *pPager;
  char *zFullPathname;
  int nameLen;
  OsFile fd;
  int rc, i;
  int tempFile;

  int readOnly = 0;
  char zTemp[SQLITE_TEMPNAME_SIZE];

  *ppPager = 0;
  if( sqlite3_malloc_failed ){
    return SQLITE_NOMEM;
  }
  if( zFilename && zFilename[0] ){






    zFullPathname = sqlite3OsFullPathname(zFilename);
    rc = sqlite3OsOpenReadWrite(zFullPathname, &fd, &readOnly);
    tempFile = 0;

  }else{
    rc = sqlite3pager_opentemp(zTemp, &fd);
    zFilename = zTemp;
    zFullPathname = sqlite3OsFullPathname(zFilename);
    tempFile = 1;
  }
  if( sqlite3_malloc_failed ){
................................................................................
  for(i=nameLen; i>0 && pPager->zDirectory[i-1]!='/'; i--){}
  if( i>0 ) pPager->zDirectory[i-1] = 0;
  strcpy(pPager->zJournal, zFullPathname);
  sqliteFree(zFullPathname);
  strcpy(&pPager->zJournal[nameLen], "-journal");
  pPager->fd = fd;
  pPager->journalOpen = 0;
  pPager->useJournal = useJournal;
  pPager->ckptOpen = 0;
  pPager->ckptInUse = 0;
  pPager->nRef = 0;
  pPager->dbSize = -1;

  pPager->ckptSize = 0;
  pPager->ckptJSize = 0;
  pPager->nPage = 0;
  pPager->mxPage = mxPage>5 ? mxPage : 10;
  pPager->state = SQLITE_UNLOCK;
  pPager->errMask = 0;
  pPager->tempFile = tempFile;

  pPager->readOnly = readOnly;
  pPager->needSync = 0;
  pPager->noSync = pPager->tempFile || !useJournal;
  pPager->pFirst = 0;
  pPager->pFirstSynced = 0;
  pPager->pLast = 0;
  pPager->nExtra = nExtra;
................................................................................
}

/*
** Forward declaration
*/
static int syncJournal(Pager*);







































































/*
** Truncate the file to the number of pages specified.
*/
int sqlite3pager_truncate(Pager *pPager, Pgno nPage){
  int rc;
  if( pPager->dbSize<0 ){
    sqlite3pager_pagecount(pPager);
................................................................................
  }
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;





  }
  syncJournal(pPager);
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)nPage);
  if( rc==SQLITE_OK ){
    pPager->dbSize = nPage;
  }
  return rc;
................................................................................
** result in a coredump.
*/
int sqlite3pager_close(Pager *pPager){
  PgHdr *pPg, *pNext;
  switch( pPager->state ){
    case SQLITE_WRITELOCK: {
      sqlite3pager_rollback(pPager);

      sqlite3OsUnlock(&pPager->fd);

      assert( pPager->journalOpen==0 );
      break;
    }
    case SQLITE_READLOCK: {

      sqlite3OsUnlock(&pPager->fd);

      break;
    }
    default: {
      /* Do nothing */
      break;
    }
  }
  for(pPg=pPager->pAll; pPg; pPg=pNext){
    pNext = pPg->pNextAll;
    sqliteFree(pPg);
  }

  sqlite3OsClose(&pPager->fd);

  assert( pPager->journalOpen==0 );
  /* Temp files are automatically deleted by the OS
  ** if( pPager->tempFile ){
  **   sqlite3OsDelete(pPager->zFilename);
  ** }
  */
  CLR_PAGER(pPager);
................................................................................
  if( pPager->errMask & ~(PAGER_ERR_FULL) ){
    return pager_errcode(pPager);
  }

  /* If this is the first page accessed, then get a read lock
  ** on the database file.
  */
  if( pPager->nRef==0 ){
    rc = sqlite3OsReadLock(&pPager->fd);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    pPager->state = SQLITE_READLOCK;

    /* If a journal file exists, try to play it back.
................................................................................
         return rc;
       }
    }
    pPg = 0;
  }else{
    /* Search for page in cache */
    pPg = pager_lookup(pPager, pgno);



  }
  if( pPg==0 ){
    /* The requested page is not in the page cache. */
    int h;
    pPager->nMiss++;
    if( pPager->nPage<pPager->mxPage || pPager->pFirst==0 ){
      /* Create a new page */
      pPg = sqliteMallocRaw( sizeof(*pPg) + SQLITE_PAGE_SIZE 
                              + sizeof(u32) + pPager->nExtra );

      if( pPg==0 ){
        pager_unwritelock(pPager);
        pPager->errMask |= PAGER_ERR_MEM;
        return SQLITE_NOMEM;
      }
      memset(pPg, 0, sizeof(*pPg));
      pPg->pPager = pPager;
      pPg->pNextAll = pPager->pAll;
      if( pPager->pAll ){
        pPager->pAll->pPrevAll = pPg;
      }
      pPg->pPrevAll = 0;
      pPager->pAll = pPg;
      pPager->nPage++;
    }else{
      /* 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( pPg->alwaysRollback ){
        pPager->alwaysRollback = 1;
      }

      /* Unlink the old page from the free list and the hash table
      */
      if( pPg==pPager->pFirstSynced ){
        PgHdr *p = pPg->pNextFree;
        while( p && p->needSync ){ p = p->pNextFree; }
        pPager->pFirstSynced = p;
      }
      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;
      if( pPg->pNextHash ){
        pPg->pNextHash->pPrevHash = pPg->pPrevHash;
      }
      if( pPg->pPrevHash ){
        pPg->pPrevHash->pNextHash = pPg->pNextHash;
      }else{
        h = pager_hash(pPg->pgno);
        assert( pPager->aHash[h]==pPg );
        pPager->aHash[h] = pPg->pNextHash;
      }
      pPg->pNextHash = pPg->pPrevHash = 0;
      pPager->nOvfl++;
    }
    pPg->pgno = pgno;
    if( pPager->aInJournal && (int)pgno<=pPager->origDbSize ){
      sqlite3CheckMemory(pPager->aInJournal, pgno/8);
      assert( pPager->journalOpen );
      pPg->inJournal = (pPager->aInJournal[pgno/8] & (1<<(pgno&7)))!=0;
      pPg->needSync = 0;
    }else{
      pPg->inJournal = 0;
      pPg->needSync = 0;
    }
    if( pPager->aInCkpt && (int)pgno<=pPager->ckptSize
             && (pPager->aInCkpt[pgno/8] & (1<<(pgno&7)))!=0 ){
      page_add_to_stmt_list(pPg);
    }else{
      page_remove_from_stmt_list(pPg);
    }
    pPg->dirty = 0;
    pPg->nRef = 1;
    REFINFO(pPg);
................................................................................
      rc = pager_errcode(pPager);
      return rc;
    }
    if( pPager->dbSize<(int)pgno ){
      memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
    }else{
      int rc;

      sqlite3OsSeek(&pPager->fd, (pgno-1)*(off_t)SQLITE_PAGE_SIZE);
      rc = sqlite3OsRead(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
      TRACE2("FETCH %d\n", pPg->pgno);
      CODEC(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
      if( rc!=SQLITE_OK ){
        off_t fileSize;
        if( sqlite3OsFileSize(&pPager->fd,&fileSize)!=SQLITE_OK
................................................................................
  PgHdr *pPg;

  assert( pPager!=0 );
  assert( pgno!=0 );
  if( pPager->errMask & ~(PAGER_ERR_FULL) ){
    return 0;
  }
  /* if( pPager->nRef==0 ){
  **  return 0;
  ** }
  */
  pPg = pager_lookup(pPager, pgno);
  if( pPg==0 ) return 0;
  page_ref(pPg);
  return PGHDR_TO_DATA(pPg);
}

/*
................................................................................
    }
  
    /* When all pages reach the freelist, drop the read lock from
    ** the database file.
    */
    pPager->nRef--;
    assert( pPager->nRef>=0 );
    if( pPager->nRef==0 ){
      pager_reset(pPager);
    }
  }
  return SQLITE_OK;
}

/*
................................................................................
  }else{
    assert( journal_format==JOURNAL_FORMAT_1 );
    rc = sqlite3OsWrite(&pPager->jfd, aJournalMagic1, sizeof(aJournalMagic1));
  }
  if( rc==SQLITE_OK ){
    rc = write32bits(&pPager->jfd, pPager->dbSize);
  }
  if( pPager->ckptAutoopen && rc==SQLITE_OK ){
    rc = sqlite3pager_stmt_begin(pPager);
  }
  if( rc!=SQLITE_OK ){
    rc = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
    }
................................................................................
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( pPager->state!=SQLITE_UNLOCK );
  if( pPager->state==SQLITE_READLOCK ){
    assert( pPager->aInJournal==0 );




    rc = sqlite3OsWriteLock(&pPager->fd);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    pPager->state = SQLITE_WRITELOCK;
    pPager->dirtyFile = 0;
    TRACE1("TRANSACTION\n");
    if( pPager->useJournal && !pPager->tempFile ){
      rc = pager_open_journal(pPager);

    }
  }
  return rc;
}

/*
** Mark a data page as writeable.  The page is written into the journal 
................................................................................
    return SQLITE_PERM;
  }

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  pPg->dirty = 1;
  if( pPg->inJournal && (pPg->inCkpt || pPager->ckptInUse==0) ){
    pPager->dirtyFile = 1;
    return SQLITE_OK;
  }

  /* If we get this far, it means that the page needs to be
  ** written to the transaction journal or the ckeckpoint journal
  ** or both.
................................................................................
  assert( pPager->journalOpen || !pPager->useJournal );
  pPager->dirtyFile = 1;

  /* The transaction journal now exists and we have a write 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 ){
    if( (int)pPg->pgno <= pPager->origDbSize ){
      int szPg;
      u32 saved;










      if( journal_format>=JOURNAL_FORMAT_3 ){
        u32 cksum = pager_cksum(pPager, pPg->pgno, pData);
        saved = *(u32*)PGHDR_TO_EXTRA(pPg);
        store32bits(cksum, pPg, SQLITE_PAGE_SIZE);
        szPg = SQLITE_PAGE_SIZE+8;
      }else{
        szPg = SQLITE_PAGE_SIZE+4;
      }
      store32bits(pPg->pgno, pPg, -4);
      CODEC(pPager, pData, pPg->pgno, 7);
      rc = sqlite3OsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
      TRACE3("JOURNAL %d %d\n", pPg->pgno, pPg->needSync);
      CODEC(pPager, pData, pPg->pgno, 0);
      if( journal_format>=JOURNAL_FORMAT_3 ){
        *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
      }
      if( rc!=SQLITE_OK ){
        sqlite3pager_rollback(pPager);
        pPager->errMask |= PAGER_ERR_FULL;
        return rc;
      }
      pPager->nRec++;
      assert( pPager->aInJournal!=0 );
      pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      pPg->needSync = !pPager->noSync;
      pPg->inJournal = 1;
      if( pPager->ckptInUse ){
        pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
        page_add_to_stmt_list(pPg);

      }
    }else{
      pPg->needSync = !pPager->journalStarted && !pPager->noSync;
      TRACE3("APPEND %d %d\n", pPg->pgno, pPg->needSync);
    }
    if( pPg->needSync ){
      pPager->needSync = 1;
    }
  }

  /* If the checkpoint journal is open and the page is not in it,
  ** then write the current page to the checkpoint journal.  Note that
  ** the checkpoint journal always uses the simplier format 2 that lacks
  ** checksums.  The header is also omitted from the checkpoint journal.
  */
  if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );









    store32bits(pPg->pgno, pPg, -4);
    CODEC(pPager, pData, pPg->pgno, 7);
    rc = sqlite3OsWrite(&pPager->cpfd, &((char*)pData)[-4], SQLITE_PAGE_SIZE+4);
    TRACE2("CKPT-JOURNAL %d\n", pPg->pgno);
    CODEC(pPager, pData, pPg->pgno, 0);
    if( rc!=SQLITE_OK ){
      sqlite3pager_rollback(pPager);
      pPager->errMask |= PAGER_ERR_FULL;
      return rc;
    }
    pPager->ckptNRec++;
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);

    page_add_to_stmt_list(pPg);
  }

  /* Update the database size and return.
  */
  if( pPager->dbSize<(int)pPg->pgno ){
    pPager->dbSize = pPg->pgno;
................................................................................
** rollback journal.
*/
void sqlite3pager_dont_rollback(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;

  if( pPager->state!=SQLITE_WRITELOCK || pPager->journalOpen==0 ) return;
  if( pPg->alwaysRollback || pPager->alwaysRollback ) return;
  if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
    assert( pPager->aInJournal!=0 );
    pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    pPg->inJournal = 1;
    if( pPager->ckptInUse ){
      pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      page_add_to_stmt_list(pPg);
    }
    TRACE2("DONT_ROLLBACK %d\n", pPg->pgno);
  }
  if( pPager->ckptInUse && !pPg->inCkpt && (int)pPg->pgno<=pPager->ckptSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_stmt_list(pPg);
  }
}












/*
** Commit all changes to the database and release the write lock.
**
** If the commit fails for any reason, a rollback attempt is made
** and an error code is returned.  If the commit worked, SQLITE_OK
** is returned.
*/
................................................................................
    rc = pager_errcode(pPager);
    return rc;
  }
  if( pPager->state!=SQLITE_WRITELOCK ){
    return SQLITE_ERROR;
  }
  TRACE1("COMMIT\n");














  if( pPager->dirtyFile==0 ){
    /* Exit early (without doing the time-consuming sqlite3OsSync() calls)
    ** if there have been no changes to the database file. */
    assert( pPager->needSync==0 );
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
................................................................................
** unless a prior malloc() failed (SQLITE_NOMEM).  Appropriate error
** codes are returned for all these occasions.  Otherwise,
** SQLITE_OK is returned.
*/
int sqlite3pager_rollback(Pager *pPager){
  int rc;
  TRACE1("ROLLBACK\n");


























  if( !pPager->dirtyFile || !pPager->journalOpen ){
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }

  if( pPager->errMask!=0 && pPager->errMask!=PAGER_ERR_FULL ){
................................................................................
  a[6] = pPager->nHit;
  a[7] = pPager->nMiss;
  a[8] = pPager->nOvfl;
  return a;
}

/*
** Set the checkpoint.
**
** This routine should be called with the transaction journal already
** open.  A new checkpoint journal is created that can be used to rollback
** changes of a single SQL command within a larger transaction.
*/
int sqlite3pager_stmt_begin(Pager *pPager){
  int rc;
  char zTemp[SQLITE_TEMPNAME_SIZE];







  if( !pPager->journalOpen ){
    pPager->ckptAutoopen = 1;
    return SQLITE_OK;
  }
  assert( pPager->journalOpen );
  assert( !pPager->ckptInUse );
  pPager->aInCkpt = sqliteMalloc( pPager->dbSize/8 + 1 );
  if( pPager->aInCkpt==0 ){
    sqlite3OsReadLock(&pPager->fd);
    return SQLITE_NOMEM;
  }
#ifndef NDEBUG
  rc = sqlite3OsFileSize(&pPager->jfd, &pPager->ckptJSize);
  if( rc ) goto ckpt_begin_failed;
  assert( pPager->ckptJSize == 
    pPager->nRec*JOURNAL_PG_SZ(journal_format)+JOURNAL_HDR_SZ(journal_format) );
#endif
  pPager->ckptJSize = pPager->nRec*JOURNAL_PG_SZ(journal_format)
                         + JOURNAL_HDR_SZ(journal_format);
  pPager->ckptSize = pPager->dbSize;
  if( !pPager->ckptOpen ){
    rc = sqlite3pager_opentemp(zTemp, &pPager->cpfd);
    if( rc ) goto ckpt_begin_failed;
    pPager->ckptOpen = 1;
    pPager->ckptNRec = 0;
  }
  pPager->ckptInUse = 1;
  return SQLITE_OK;
 
ckpt_begin_failed:
  if( pPager->aInCkpt ){
    sqliteFree(pPager->aInCkpt);
    pPager->aInCkpt = 0;
  }
  return rc;
}

/*
** Commit a checkpoint.
*/
int sqlite3pager_stmt_commit(Pager *pPager){
  if( pPager->ckptInUse ){
    PgHdr *pPg, *pNext;


    sqlite3OsSeek(&pPager->cpfd, 0);
    /* sqlite3OsTruncate(&pPager->cpfd, 0); */
    pPager->ckptNRec = 0;
    pPager->ckptInUse = 0;
    sqliteFree( pPager->aInCkpt );
    pPager->aInCkpt = 0;

    for(pPg=pPager->pCkpt; pPg; pPg=pNext){
      pNext = pPg->pNextCkpt;
      assert( pPg->inCkpt );
      pPg->inCkpt = 0;
      pPg->pPrevCkpt = pPg->pNextCkpt = 0;




    }



    pPager->pCkpt = 0;
  }
  pPager->ckptAutoopen = 0;
  return SQLITE_OK;
}

/*
** Rollback a checkpoint.
*/
int sqlite3pager_stmt_rollback(Pager *pPager){
  int rc;


  if( pPager->ckptInUse ){













    rc = pager_stmt_playback(pPager);

    sqlite3pager_stmt_commit(pPager);
  }else{
    rc = SQLITE_OK;
  }
  pPager->ckptAutoopen = 0;
  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlite3pager_filename(Pager *pPager){

** 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 1.107 2004/05/12 13:30:08 drh Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
** database file.
*/
typedef struct PgHdr PgHdr;
struct PgHdr {
  Pager *pPager;                 /* The pager to which this page belongs */
  Pgno pgno;                     /* The page number for this page */
  PgHdr *pNextHash, *pPrevHash;  /* Hash collision chain for PgHdr.pgno */

  PgHdr *pNextFree, *pPrevFree;  /* Freelist of pages where nRef==0 */
  PgHdr *pNextAll;               /* A list of all pages */

  PgHdr *pNextStmt, *pPrevStmt;  /* List of pages in the statement journal */
  u8 inJournal;                  /* TRUE if has been written to journal */
  u8 inStmt;                     /* TRUE if in the statement subjournal */
  u8 dirty;                      /* TRUE if we need to write back changes */
  u8 needSync;                   /* Sync journal before writing this page */
  u8 alwaysRollback;             /* Disable dont_rollback() for this page */
  short int nRef;                /* Number of users of this page */
  PgHdr *pDirty;                 /* Dirty pages sorted by PgHdr.pgno */
  /* SQLITE_PAGE_SIZE bytes of page data follow this header */
  /* Pager.nExtra bytes of local data follow the page data */
};

/*
** For an in-memory only database, some extra information is recorded about
** each page so that changes can be rolled back.  (Journal files are not
** used for in-memory databases.)  The following information is added to
** the end of every EXTRA block for in-memory databases.
**
** This information could have been added directly to the PgHdr structure.
** But then it would take up an extra 8 bytes of storage on every PgHdr
** even for disk-based databases.  Splitting it out saves 8 bytes.  This
** is only a savings of 0.8% but those percentages add up.
*/
typedef struct PgHistory PgHistory;
struct PgHistory {
  u8 *pOrig;     /* Original page text.  Restore to this on a full rollback */
  u8 *pStmt;     /* Text as it was at the beginning of the current statement */
};

/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC(P,D,N,X) if( P->xCodec ){ P->xCodec(P->pCodecArg,D,N,X); }
#else
................................................................................
/*
** 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(P) ((void*)&((char*)(&(P)[1]))[SQLITE_PAGE_SIZE])
#define PGHDR_TO_HIST(P,PGR)  \
            ((PgHistory*)&((char*)(&(P)[1]))[(PGR)->pageSize+(PGR)->nExtra])

/*
** How big to make the hash table used for locating in-memory pages
** by page number.
*/
#define N_PG_HASH 2048

................................................................................
** A open page cache is an instance of the following structure.
*/
struct Pager {
  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*/
  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() */
  off_t stmtJSize;            /* Size of journal 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 */
  void (*xDestructor)(void*); /* Call this routine when freeing pages */
  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 */
  int nHit, nMiss, nOvfl;     /* Cache hits, missing, and LRU overflows */
  void (*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
  void *pCodecArg;            /* First argument to xCodec() */
  int pageSize;               /* Page size in bytes */
  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 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 state;                   /* SQLITE_UNLOCK, _READLOCK or _WRITELOCK */
  u8 errMask;                 /* One of several kinds of errors */
  u8 tempFile;                /* zFilename is a temporary file */
  u8 readOnly;                /* True for a read-only database */
  u8 needSync;                /* True if an fsync() is needed on the journal */
  u8 dirtyFile;               /* True if database file has changed in any way */
  u8 alwaysRollback;          /* Disable dont_rollback() for all pages */
  u8 memDb;                   /* True to inhibit all file I/O */
  u8 *aInJournal;             /* One bit for each page in the database file */
  u8 *aInStmt;                /* One bit for each page in the database */
  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 *aHash[N_PG_HASH];    /* Hash table to map page number of PgHdr */
};

/*
** These are bits that can be set in Pager.errMask.
*/
#define PAGER_ERR_FULL     0x01  /* a write() failed */
................................................................................
/*
** The following integer determines what format to use when creating
** new primary journal files.  By default we always use format 3.
** When testing, we can set this value to older journal formats in order to
** make sure that newer versions of the library are able to rollback older
** journal files.
**
** Note that statement journals always use format 2 and omit the header.
*/
#ifdef SQLITE_TEST
int journal_format = 3;
#else
# define journal_format 3
#endif

................................................................................
  if( pPager->errMask & PAGER_ERR_MEM )     rc = SQLITE_NOMEM;
  if( pPager->errMask & PAGER_ERR_CORRUPT ) rc = SQLITE_CORRUPT;
  return rc;
}

/*
** Add or remove a page from the list of all pages that are in the
** statement journal.
**
** The Pager keeps a separate list of pages that are currently in
** the statement journal.  This helps the sqlite3pager_stmt_commit()
** routine run MUCH faster for the common case where there are many
** pages in memory but only a few are in the statement journal.
*/
static void page_add_to_stmt_list(PgHdr *pPg){
  Pager *pPager = pPg->pPager;
  if( pPg->inStmt ) return;
  assert( pPg->pPrevStmt==0 && pPg->pNextStmt==0 );
  pPg->pPrevStmt = 0;
  if( pPager->pStmt ){
    pPager->pStmt->pPrevStmt = pPg;
  }
  pPg->pNextStmt = pPager->pStmt;
  pPager->pStmt = pPg;
  pPg->inStmt = 1;
}
static void page_remove_from_stmt_list(PgHdr *pPg){
  if( !pPg->inStmt ) return;
  if( pPg->pPrevStmt ){
    assert( pPg->pPrevStmt->pNextStmt==pPg );
    pPg->pPrevStmt->pNextStmt = pPg->pNextStmt;
  }else{
    assert( pPg->pPager->pStmt==pPg );
    pPg->pPager->pStmt = pPg->pNextStmt;
  }
  if( pPg->pNextStmt ){
    assert( pPg->pNextStmt->pPrevStmt==pPg );
    pPg->pNextStmt->pPrevStmt = pPg->pPrevStmt;
  }
  pPg->pNextStmt = 0;
  pPg->pPrevStmt = 0;
  pPg->inStmt = 0;
}

/*
** Find a page in the hash table given its page number.  Return
** a pointer to the page or NULL if not found.
*/
static PgHdr *pager_lookup(Pager *pPager, Pgno pgno){
................................................................................
** a file is an expensive operation.
*/
static int pager_unwritelock(Pager *pPager){
  int rc;
  PgHdr *pPg;
  if( pPager->state<SQLITE_WRITELOCK ) return SQLITE_OK;
  sqlite3pager_stmt_commit(pPager);
  if( pPager->stmtOpen ){
    sqlite3OsClose(&pPager->stfd);
    pPager->stmtOpen = 0;
  }
  if( pPager->journalOpen ){
    sqlite3OsClose(&pPager->jfd);
    pPager->journalOpen = 0;
    sqlite3OsDelete(pPager->zJournal);
    sqliteFree( pPager->aInJournal );
    pPager->aInJournal = 0;
................................................................................
  }else{
    rc = pager_unwritelock(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){
  off_t szJ;               /* Size of the full journal */
  int nRec;                /* Number of Records */
  int i;                   /* Loop counter */
  int rc;

  /* Truncate the database back to its original size.
  */
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)pPager->stmtSize);
  pPager->dbSize = pPager->stmtSize;

  /* Figure out how many records are in the statement journal.
  */
  assert( pPager->stmtInUse && pPager->journalOpen );
  sqlite3OsSeek(&pPager->stfd, 0);
  nRec = pPager->stmtNRec;
  
  /* Copy original pages out of the statement journal and back into the
  ** database file.  Note that the statement journal always uses format
  ** 2 instead of format 3 since it does not need to be concerned with
  ** power failures corrupting the journal and can thus omit the checksums.
  */
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->stfd, 2);
    assert( rc!=SQLITE_DONE );
    if( rc!=SQLITE_OK ) goto end_stmt_playback;
  }

  /* Figure out how many pages need to be copied out of the transaction
  ** journal.
  */
  rc = sqlite3OsSeek(&pPager->jfd, pPager->stmtJSize);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  rc = sqlite3OsFileSize(&pPager->jfd, &szJ);
  if( rc!=SQLITE_OK ){
    goto end_stmt_playback;
  }
  nRec = (szJ - pPager->stmtJSize)/JOURNAL_PG_SZ(journal_format);
  for(i=nRec-1; i>=0; i--){
    rc = pager_playback_one_page(pPager, &pPager->jfd, journal_format);
    if( rc!=SQLITE_OK ){
      assert( rc!=SQLITE_DONE );
      goto end_stmt_playback;
    }
  }
................................................................................
){
  Pager *pPager;
  char *zFullPathname;
  int nameLen;
  OsFile fd;
  int rc, i;
  int tempFile;
  int memDb = 0;
  int readOnly = 0;
  char zTemp[SQLITE_TEMPNAME_SIZE];

  *ppPager = 0;
  if( sqlite3_malloc_failed ){
    return SQLITE_NOMEM;
  }
  if( zFilename && zFilename[0] ){
    if( strcmp(zFilename,":memory:")==0 ){
      memDb = 1;
      zFullPathname = sqliteMalloc(4);
      if( zFullPathname ) strcpy(zFullPathname, "nil");
      rc = SQLITE_OK;
    }else{
      zFullPathname = sqlite3OsFullPathname(zFilename);
      rc = sqlite3OsOpenReadWrite(zFullPathname, &fd, &readOnly);
      tempFile = 0;
    }
  }else{
    rc = sqlite3pager_opentemp(zTemp, &fd);
    zFilename = zTemp;
    zFullPathname = sqlite3OsFullPathname(zFilename);
    tempFile = 1;
  }
  if( sqlite3_malloc_failed ){
................................................................................
  for(i=nameLen; i>0 && pPager->zDirectory[i-1]!='/'; i--){}
  if( i>0 ) pPager->zDirectory[i-1] = 0;
  strcpy(pPager->zJournal, zFullPathname);
  sqliteFree(zFullPathname);
  strcpy(&pPager->zJournal[nameLen], "-journal");
  pPager->fd = fd;
  pPager->journalOpen = 0;
  pPager->useJournal = useJournal && !memDb;
  pPager->stmtOpen = 0;
  pPager->stmtInUse = 0;
  pPager->nRef = 0;
  pPager->dbSize = memDb-1;
  pPager->pageSize = SQLITE_PAGE_SIZE;
  pPager->stmtSize = 0;
  pPager->stmtJSize = 0;
  pPager->nPage = 0;
  pPager->mxPage = mxPage>5 ? mxPage : 10;
  pPager->state = SQLITE_UNLOCK;
  pPager->errMask = 0;
  pPager->tempFile = tempFile;
  pPager->memDb = memDb;
  pPager->readOnly = readOnly;
  pPager->needSync = 0;
  pPager->noSync = pPager->tempFile || !useJournal;
  pPager->pFirst = 0;
  pPager->pFirstSynced = 0;
  pPager->pLast = 0;
  pPager->nExtra = nExtra;
................................................................................
}

/*
** Forward declaration
*/
static int syncJournal(Pager*);


/*
** 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 */
  if( pPg->pNextHash ){
    pPg->pNextHash->pPrevHash = pPg->pPrevHash;
  }
  if( pPg->pPrevHash ){
    pPg->pPrevHash->pNextHash = pPg->pNextHash;
  }else{
    int h = pager_hash(pPg->pgno);
    assert( pPager->aHash[h]==pPg );
    pPager->aHash[h] = pPg->pNextHash;
  }
  pPg->pNextHash = pPg->pPrevHash = 0;
}

/*
** This routine is used to truncate an in-memory database.  Delete
** every pages whose pgno is larger than pPager->dbSize and is unreferenced.
** Referenced pages larger than pPager->dbSize are zeroed.
*/
static void memoryTruncate(Pager *pPager){
  PgHdr *pPg;
  PgHdr **ppPg;
  int dbSize = pPager->dbSize;

  ppPg = &pPager->pAll;
  while( (pPg = *ppPg)!=0 ){
    if( pPg->pgno<=dbSize ){
      ppPg = &pPg->pNextAll;
    }else if( pPg->nRef>0 ){
      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
      ppPg = &pPg->pNextAll;
    }else{
      *ppPg = pPg->pNextAll;
      unlinkPage(pPg);
      sqliteFree(pPg);
      pPager->nPage--;
    }
  }
}

/*
** Truncate the file to the number of pages specified.
*/
int sqlite3pager_truncate(Pager *pPager, Pgno nPage){
  int rc;
  if( pPager->dbSize<0 ){
    sqlite3pager_pagecount(pPager);
................................................................................
  }
  if( pPager->errMask!=0 ){
    rc = pager_errcode(pPager);
    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
  if( pPager->memDb ){
    pPager->dbSize = nPage;
    memoryTruncate(pPager);
    return SQLITE_OK;
  }
  syncJournal(pPager);
  rc = sqlite3OsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)nPage);
  if( rc==SQLITE_OK ){
    pPager->dbSize = nPage;
  }
  return rc;
................................................................................
** result in a coredump.
*/
int sqlite3pager_close(Pager *pPager){
  PgHdr *pPg, *pNext;
  switch( pPager->state ){
    case SQLITE_WRITELOCK: {
      sqlite3pager_rollback(pPager);
      if( !pPager->memDb ){
        sqlite3OsUnlock(&pPager->fd);
      }
      assert( pPager->journalOpen==0 );
      break;
    }
    case SQLITE_READLOCK: {
      if( !pPager->memDb ){
        sqlite3OsUnlock(&pPager->fd);
      }
      break;
    }
    default: {
      /* Do nothing */
      break;
    }
  }
  for(pPg=pPager->pAll; pPg; pPg=pNext){
    pNext = pPg->pNextAll;
    sqliteFree(pPg);
  }
  if( !pPager->memDb ){
    sqlite3OsClose(&pPager->fd);
  }
  assert( pPager->journalOpen==0 );
  /* Temp files are automatically deleted by the OS
  ** if( pPager->tempFile ){
  **   sqlite3OsDelete(pPager->zFilename);
  ** }
  */
  CLR_PAGER(pPager);
................................................................................
  if( pPager->errMask & ~(PAGER_ERR_FULL) ){
    return pager_errcode(pPager);
  }

  /* If this is the first page accessed, then get a read lock
  ** on the database file.
  */
  if( pPager->nRef==0 && !pPager->memDb ){
    rc = sqlite3OsReadLock(&pPager->fd);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    pPager->state = SQLITE_READLOCK;

    /* If a journal file exists, try to play it back.
................................................................................
         return rc;
       }
    }
    pPg = 0;
  }else{
    /* Search for page in cache */
    pPg = pager_lookup(pPager, pgno);
    if( pPager->memDb && pPager->state==SQLITE_UNLOCK ){
      pPager->state = SQLITE_READLOCK;
    }
  }
  if( pPg==0 ){
    /* The requested page is not in the page cache. */
    int h;
    pPager->nMiss++;
    if( pPager->nPage<pPager->mxPage || pPager->pFirst==0 || pPager->memDb ){
      /* Create a new page */
      pPg = sqliteMallocRaw( sizeof(*pPg) + SQLITE_PAGE_SIZE 
                              + sizeof(u32) + pPager->nExtra
                              + pPager->memDb*sizeof(PgHistory) );
      if( pPg==0 ){
        pager_unwritelock(pPager);
        pPager->errMask |= PAGER_ERR_MEM;
        return SQLITE_NOMEM;
      }
      memset(pPg, 0, sizeof(*pPg));
      if( pPager->memDb ){
        memset(PGHDR_TO_HIST(pPg, pPager), 0, sizeof(PgHistory));
      }
      pPg->pPager = pPager;
      pPg->pNextAll = pPager->pAll;

      pPager->pAll = pPg;
      pPager->nPage++;
    }else{
      /* 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( pPg->alwaysRollback ){
        pPager->alwaysRollback = 1;
      }

      /* Unlink the old page from the free list and the hash table
      */
      unlinkPage(pPg);




























      pPager->nOvfl++;
    }
    pPg->pgno = pgno;
    if( pPager->aInJournal && (int)pgno<=pPager->origDbSize ){
      sqlite3CheckMemory(pPager->aInJournal, pgno/8);
      assert( pPager->journalOpen );
      pPg->inJournal = (pPager->aInJournal[pgno/8] & (1<<(pgno&7)))!=0;
      pPg->needSync = 0;
    }else{
      pPg->inJournal = 0;
      pPg->needSync = 0;
    }
    if( pPager->aInStmt && (int)pgno<=pPager->stmtSize
             && (pPager->aInStmt[pgno/8] & (1<<(pgno&7)))!=0 ){
      page_add_to_stmt_list(pPg);
    }else{
      page_remove_from_stmt_list(pPg);
    }
    pPg->dirty = 0;
    pPg->nRef = 1;
    REFINFO(pPg);
................................................................................
      rc = pager_errcode(pPager);
      return rc;
    }
    if( pPager->dbSize<(int)pgno ){
      memset(PGHDR_TO_DATA(pPg), 0, SQLITE_PAGE_SIZE);
    }else{
      int rc;
      assert( pPager->memDb==0 );
      sqlite3OsSeek(&pPager->fd, (pgno-1)*(off_t)SQLITE_PAGE_SIZE);
      rc = sqlite3OsRead(&pPager->fd, PGHDR_TO_DATA(pPg), SQLITE_PAGE_SIZE);
      TRACE2("FETCH %d\n", pPg->pgno);
      CODEC(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
      if( rc!=SQLITE_OK ){
        off_t fileSize;
        if( sqlite3OsFileSize(&pPager->fd,&fileSize)!=SQLITE_OK
................................................................................
  PgHdr *pPg;

  assert( pPager!=0 );
  assert( pgno!=0 );
  if( pPager->errMask & ~(PAGER_ERR_FULL) ){
    return 0;
  }




  pPg = pager_lookup(pPager, pgno);
  if( pPg==0 ) return 0;
  page_ref(pPg);
  return PGHDR_TO_DATA(pPg);
}

/*
................................................................................
    }
  
    /* 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->memDb ){
      pager_reset(pPager);
    }
  }
  return SQLITE_OK;
}

/*
................................................................................
  }else{
    assert( journal_format==JOURNAL_FORMAT_1 );
    rc = sqlite3OsWrite(&pPager->jfd, aJournalMagic1, sizeof(aJournalMagic1));
  }
  if( rc==SQLITE_OK ){
    rc = write32bits(&pPager->jfd, pPager->dbSize);
  }
  if( pPager->stmtAutoopen && rc==SQLITE_OK ){
    rc = sqlite3pager_stmt_begin(pPager);
  }
  if( rc!=SQLITE_OK ){
    rc = pager_unwritelock(pPager);
    if( rc==SQLITE_OK ){
      rc = SQLITE_FULL;
    }
................................................................................
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;
  int rc = SQLITE_OK;
  assert( pPg->nRef>0 );
  assert( pPager->state!=SQLITE_UNLOCK );
  if( pPager->state==SQLITE_READLOCK ){
    assert( pPager->aInJournal==0 );
    if( pPager->memDb ){
      pPager->state = SQLITE_WRITELOCK;
      pPager->origDbSize = pPager->dbSize;
    }else{
      rc = sqlite3OsWriteLock(&pPager->fd);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      pPager->state = SQLITE_WRITELOCK;
      pPager->dirtyFile = 0;
      TRACE1("TRANSACTION\n");
      if( pPager->useJournal && !pPager->tempFile ){
        rc = pager_open_journal(pPager);
      }
    }
  }
  return rc;
}

/*
** Mark a data page as writeable.  The page is written into the journal 
................................................................................
    return SQLITE_PERM;
  }

  /* Mark the page as dirty.  If the page has already been written
  ** to the journal then we can return right away.
  */
  pPg->dirty = 1;
  if( pPg->inJournal && (pPg->inStmt || pPager->stmtInUse==0) ){
    pPager->dirtyFile = 1;
    return SQLITE_OK;
  }

  /* If we get this far, it means that the page needs to be
  ** written to the transaction journal or the ckeckpoint journal
  ** or both.
................................................................................
  assert( pPager->journalOpen || !pPager->useJournal );
  pPager->dirtyFile = 1;

  /* The transaction journal now exists and we have a write 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 || pPager->memDb) ){
    if( (int)pPg->pgno <= pPager->origDbSize ){
      int szPg;
      u32 saved;
      if( pPager->memDb ){
        PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
        TRACE2("JOURNAL %d\n", pPg->pgno);
        assert( pHist->pOrig==0 );
        pHist->pOrig = sqliteMallocRaw( pPager->pageSize );
        if( pHist->pOrig ){
          memcpy(pHist->pOrig, PGHDR_TO_DATA(pPg), pPager->pageSize);
        }
        pPg->inJournal = 1;
      }else {
        if( journal_format>=JOURNAL_FORMAT_3 ){
          u32 cksum = pager_cksum(pPager, pPg->pgno, pData);
          saved = *(u32*)PGHDR_TO_EXTRA(pPg);
          store32bits(cksum, pPg, SQLITE_PAGE_SIZE);
          szPg = SQLITE_PAGE_SIZE+8;
        }else{
          szPg = SQLITE_PAGE_SIZE+4;
        }
        store32bits(pPg->pgno, pPg, -4);
        CODEC(pPager, pData, pPg->pgno, 7);
        rc = sqlite3OsWrite(&pPager->jfd, &((char*)pData)[-4], szPg);
        TRACE3("JOURNAL %d %d\n", pPg->pgno, pPg->needSync);
        CODEC(pPager, pData, pPg->pgno, 0);
        if( journal_format>=JOURNAL_FORMAT_3 ){
          *(u32*)PGHDR_TO_EXTRA(pPg) = saved;
        }
        if( rc!=SQLITE_OK ){
          sqlite3pager_rollback(pPager);
          pPager->errMask |= PAGER_ERR_FULL;
          return rc;
        }
        pPager->nRec++;
        assert( pPager->aInJournal!=0 );
        pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
        pPg->needSync = !pPager->noSync;
        pPg->inJournal = 1;
        if( pPager->stmtInUse ){
          pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
          page_add_to_stmt_list(pPg);
        }
      }
    }else{
      pPg->needSync = !pPager->journalStarted && !pPager->noSync;
      TRACE3("APPEND %d %d\n", pPg->pgno, pPg->needSync);
    }
    if( pPg->needSync ){
      pPager->needSync = 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 always uses the simplier format 2 that lacks
  ** checksums.  The header is also omitted from the statement journal.
  */
  if( pPager->stmtInUse && !pPg->inStmt && (int)pPg->pgno<=pPager->stmtSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    if( pPager->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);
      }
      TRACE2("STMT-JOURNAL %d\n", pPg->pgno);
    }else{
      store32bits(pPg->pgno, pPg, -4);
      CODEC(pPager, pData, pPg->pgno, 7);
      rc = sqlite3OsWrite(&pPager->stfd, ((char*)pData)-4, SQLITE_PAGE_SIZE+4);
      TRACE2("STMT-JOURNAL %d\n", pPg->pgno);
      CODEC(pPager, pData, pPg->pgno, 0);
      if( rc!=SQLITE_OK ){
        sqlite3pager_rollback(pPager);
        pPager->errMask |= PAGER_ERR_FULL;
        return rc;
      }
      pPager->stmtNRec++;
      assert( pPager->aInStmt!=0 );
      pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    }
    page_add_to_stmt_list(pPg);
  }

  /* Update the database size and return.
  */
  if( pPager->dbSize<(int)pPg->pgno ){
    pPager->dbSize = pPg->pgno;
................................................................................
** rollback journal.
*/
void sqlite3pager_dont_rollback(void *pData){
  PgHdr *pPg = DATA_TO_PGHDR(pData);
  Pager *pPager = pPg->pPager;

  if( pPager->state!=SQLITE_WRITELOCK || pPager->journalOpen==0 ) return;
  if( pPg->alwaysRollback || pPager->alwaysRollback || pPager->memDb ) return;
  if( !pPg->inJournal && (int)pPg->pgno <= pPager->origDbSize ){
    assert( pPager->aInJournal!=0 );
    pPager->aInJournal[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    pPg->inJournal = 1;
    if( pPager->stmtInUse ){
      pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
      page_add_to_stmt_list(pPg);
    }
    TRACE2("DONT_ROLLBACK %d\n", pPg->pgno);
  }
  if( pPager->stmtInUse && !pPg->inStmt && (int)pPg->pgno<=pPager->stmtSize ){
    assert( pPg->inJournal || (int)pPg->pgno>pPager->origDbSize );
    assert( pPager->aInStmt!=0 );
    pPager->aInStmt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_stmt_list(pPg);
  }
}


/*
** Clear a PgHistory block
*/
static void clearHistory(PgHistory *pHist){
  sqliteFree(pHist->pOrig);
  sqliteFree(pHist->pStmt);
  pHist->pOrig = 0;
  pHist->pStmt = 0;
}

/*
** 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.
*/
................................................................................
    rc = pager_errcode(pPager);
    return rc;
  }
  if( pPager->state!=SQLITE_WRITELOCK ){
    return SQLITE_ERROR;
  }
  TRACE1("COMMIT\n");
  if( pPager->memDb ){
    pPg = pager_get_all_dirty_pages(pPager);
    while( pPg ){
      clearHistory(PGHDR_TO_HIST(pPg, pPager));
      pPg->dirty = 0;
      pPg->inJournal = 0;
      pPg->inStmt = 0;
      pPg->pPrevStmt = pPg->pNextStmt = 0;
      pPg = pPg->pDirty;
    }
    pPager->pStmt = 0;
    pPager->state = SQLITE_READLOCK;
    return SQLITE_OK;
  }
  if( pPager->dirtyFile==0 ){
    /* Exit early (without doing the time-consuming sqlite3OsSync() calls)
    ** if there have been no changes to the database file. */
    assert( pPager->needSync==0 );
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
................................................................................
** unless a prior malloc() failed (SQLITE_NOMEM).  Appropriate error
** codes are returned for all these occasions.  Otherwise,
** SQLITE_OK is returned.
*/
int sqlite3pager_rollback(Pager *pPager){
  int rc;
  TRACE1("ROLLBACK\n");
  if( pPager->memDb ){
    PgHdr *p;
    for(p=pPager->pAll; p; p=p->pNextAll){
      PgHistory *pHist;
      if( !p->dirty ) continue;
      pHist = PGHDR_TO_HIST(p, pPager);
      if( pHist->pOrig ){
        memcpy(PGHDR_TO_DATA(p), pHist->pOrig, pPager->pageSize);
        TRACE2("ROLLBACK-PAGE %d\n", p->pgno);
      }else{
        TRACE2("PAGE %d is clean\n", p->pgno);
      }
      clearHistory(pHist);
      p->dirty = 0;
      p->inJournal = 0;
      p->inStmt = 0;
      p->pPrevStmt = p->pNextStmt = 0;
    }
    pPager->pStmt = 0;
    pPager->dbSize = pPager->origDbSize;
    memoryTruncate(pPager);
    pPager->stmtInUse = 0;
    pPager->state = SQLITE_READLOCK;
    return SQLITE_OK;
  }

  if( !pPager->dirtyFile || !pPager->journalOpen ){
    rc = pager_unwritelock(pPager);
    pPager->dbSize = -1;
    return rc;
  }

  if( pPager->errMask!=0 && pPager->errMask!=PAGER_ERR_FULL ){
................................................................................
  a[6] = pPager->nHit;
  a[7] = pPager->nMiss;
  a[8] = pPager->nOvfl;
  return a;
}

/*
** Set the statement rollback point.
**
** This routine should be called with the transaction journal already
** open.  A new statement journal is created that can be used to rollback
** changes of a single SQL command within a larger transaction.
*/
int sqlite3pager_stmt_begin(Pager *pPager){
  int rc;
  char zTemp[SQLITE_TEMPNAME_SIZE];
  assert( !pPager->stmtInUse );
  TRACE1("STMT-BEGIN\n");
  if( pPager->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 ){
    sqlite3OsReadLock(&pPager->fd);
    return SQLITE_NOMEM;
  }
#ifndef NDEBUG
  rc = sqlite3OsFileSize(&pPager->jfd, &pPager->stmtJSize);
  if( rc ) goto stmt_begin_failed;
  assert( pPager->stmtJSize == 
    pPager->nRec*JOURNAL_PG_SZ(journal_format)+JOURNAL_HDR_SZ(journal_format) );
#endif
  pPager->stmtJSize = pPager->nRec*JOURNAL_PG_SZ(journal_format)
                         + JOURNAL_HDR_SZ(journal_format);
  pPager->stmtSize = pPager->dbSize;
  if( !pPager->stmtOpen ){
    rc = sqlite3pager_opentemp(zTemp, &pPager->stfd);
    if( rc ) goto stmt_begin_failed;
    pPager->stmtOpen = 1;
    pPager->stmtNRec = 0;
  }
  pPager->stmtInUse = 1;
  return SQLITE_OK;
 
stmt_begin_failed:
  if( pPager->aInStmt ){
    sqliteFree(pPager->aInStmt);
    pPager->aInStmt = 0;
  }
  return rc;
}

/*
** Commit a statement.
*/
int sqlite3pager_stmt_commit(Pager *pPager){
  if( pPager->stmtInUse ){
    PgHdr *pPg, *pNext;
    TRACE1("STMT-COMMIT\n");
    if( !pPager->memDb ){
      sqlite3OsSeek(&pPager->stfd, 0);
      /* sqlite3OsTruncate(&pPager->stfd, 0); */


      sqliteFree( pPager->aInStmt );
      pPager->aInStmt = 0;
    }
    for(pPg=pPager->pStmt; pPg; pPg=pNext){
      pNext = pPg->pNextStmt;
      assert( pPg->inStmt );
      pPg->inStmt = 0;
      pPg->pPrevStmt = pPg->pNextStmt = 0;
      if( pPager->memDb ){
        PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
        sqliteFree(pHist->pStmt);
        pHist->pStmt = 0;
      }
    }
    pPager->stmtNRec = 0;
    pPager->stmtInUse = 0;
    pPager->pStmt = 0;
  }
  pPager->stmtAutoopen = 0;
  return SQLITE_OK;
}

/*
** Rollback a statement.
*/
int sqlite3pager_stmt_rollback(Pager *pPager){
  int rc;
  if( pPager->stmtInUse ){
    TRACE1("STMT-ROLLBACK\n");
    if( pPager->memDb ){
      PgHdr *pPg;
      for(pPg=pPager->pStmt; pPg; pPg=pPg->pNextStmt){
        PgHistory *pHist = PGHDR_TO_HIST(pPg, pPager);
        if( pHist->pStmt ){
          memcpy(PGHDR_TO_DATA(pPg), pHist->pStmt, pPager->pageSize);
          sqliteFree(pHist->pStmt);
          pHist->pStmt = 0;
        }
      }
      pPager->dbSize = pPager->stmtSize;
      memoryTruncate(pPager);
      rc = SQLITE_OK;
    }else{
      rc = pager_stmt_playback(pPager);
    }
    sqlite3pager_stmt_commit(pPager);
  }else{
    rc = SQLITE_OK;
  }
  pPager->stmtAutoopen = 0;
  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlite3pager_filename(Pager *pPager){

# 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 file implements regression tests for SQLite library.  The
# focus of this script is page cache subsystem.
#
# $Id: pager2.test,v 1.1 2004/05/12 13:30:09 drh Exp $


set testdir [file dirname $argv0]
source $testdir/tester.tcl

if {[info commands pager_open]!=""} {
db close

# Basic sanity check.  Open and close a pager.
#
do_test pager2-1.0 {
  set v [catch {
    set ::p1 [pager_open :memory: 10]
  } msg]
} {0}
do_test pager2-1.1 {
  pager_stats $::p1
} {ref 0 page 0 max 10 size 0 state 0 err 0 hit 0 miss 0 ovfl 0}
do_test pager2-1.2 {
  pager_pagecount $::p1
} {0}
do_test pager2-1.3 {
  pager_stats $::p1
} {ref 0 page 0 max 10 size 0 state 0 err 0 hit 0 miss 0 ovfl 0}
do_test pager2-1.4 {
  pager_close $::p1
} {}

# Try to write a few pages.
#
do_test pager2-2.1 {
  set v [catch {
    set ::p1 [pager_open :memory: 10]
  } msg]
} {0}
#do_test pager2-2.2 {
#  set v [catch {
#    set ::g1 [page_get $::p1 0]
#  } msg]
#  lappend v $msg
#} {1 SQLITE_ERROR}
do_test pager2-2.3.1 {
  set ::gx [page_lookup $::p1 1]
} {}
do_test pager2-2.3.2 {
  pager_stats $::p1
} {ref 0 page 0 max 10 size 0 state 0 err 0 hit 0 miss 0 ovfl 0}
do_test pager2-2.3.3 {
  set v [catch {
    set ::g1 [page_get $::p1 1]
  } msg]
  if {$v} {lappend v $msg}
  set v
} {0}
do_test pager2-2.3.3 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 0 state 1 err 0 hit 0 miss 1 ovfl 0}
do_test pager2-2.3.4 {
  set ::gx [page_lookup $::p1 1]
  expr {$::gx!=""}
} {1}
do_test pager2-2.3.5 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 0 state 1 err 0 hit 0 miss 1 ovfl 0}
do_test pager2-2.3.6 {
  expr $::g1==$::gx
} {1}
do_test pager2-2.3.7 {
  page_unref $::gx
  pager_stats $::p1
} {ref 1 page 1 max 10 size 0 state 1 err 0 hit 0 miss 1 ovfl 0}
do_test pager2-2.4 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 0 state 1 err 0 hit 0 miss 1 ovfl 0}
do_test pager2-2.5 {
  pager_pagecount $::p1
} {0}
do_test pager2-2.6 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 0 state 1 err 0 hit 0 miss 1 ovfl 0}
do_test pager2-2.7 {
  page_number $::g1
} {1}
do_test pager2-2.8 {
  page_read $::g1
} {}
do_test pager2-2.9 {
  page_unref $::g1
} {}
do_test pager2-2.10 {
  pager_stats $::p1
} {ref 0 page 1 max 10 size 0 state 1 err 0 hit 0 miss 1 ovfl 0}
do_test pager2-2.11 {
  set ::g1 [page_get $::p1 1]
  expr {$::g1!=0}
} {1}
do_test pager2-2.12 {
  page_number $::g1
} {1}
do_test pager2-2.13 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 0 state 1 err 0 hit 1 miss 1 ovfl 0}
do_test pager2-2.14 {
  set v [catch {
    page_write $::g1 "Page-One"
  } msg]
  lappend v $msg
} {0 {}}
do_test pager2-2.15 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 1 state 2 err 0 hit 1 miss 1 ovfl 0}
do_test pager2-2.16 {
  page_read $::g1
} {Page-One}
do_test pager2-2.17 {
  set v [catch {
    pager_commit $::p1
  } msg]
  lappend v $msg
} {0 {}}
do_test pager2-2.20 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 1 state 1 err 0 hit 1 miss 1 ovfl 0}
do_test pager2-2.19 {
  pager_pagecount $::p1
} {1}
do_test pager2-2.21 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 1 state 1 err 0 hit 1 miss 1 ovfl 0}
do_test pager2-2.22 {
  page_unref $::g1
} {}
do_test pager2-2.23 {
  pager_stats $::p1
} {ref 0 page 1 max 10 size 1 state 1 err 0 hit 1 miss 1 ovfl 0}
do_test pager2-2.24 {
  set v [catch {
    page_get $::p1 1
  } ::g1]
  if {$v} {lappend v $::g1}
  set v
} {0}
do_test pager2-2.25 {
  page_read $::g1
} {Page-One}
do_test pager2-2.26 {
  set v [catch {
    page_write $::g1 {page-one}
  } msg]
  lappend v $msg
} {0 {}}
do_test pager2-2.27 {
  page_read $::g1
} {page-one}
do_test pager2-2.28 {
  set v [catch {
    pager_rollback $::p1
  } msg]
  lappend v $msg
} {0 {}}
do_test pager2-2.29 {
  page_unref $::g1
  set ::g1 [page_get $::p1 1]
  page_read $::g1
} {Page-One}
#do_test pager2-2.99 {
#  pager_close $::p1
#} {}

#do_test pager2-3.1 {
#  set v [catch {
#    set ::p1 [pager_open :memory: 15]
#  } msg]
#  if {$v} {lappend v $msg}
#  set v
#} {0}
do_test pager2-3.2 {
  pager_pagecount $::p1
} {1}
do_test pager2-3.3 {
  set v [catch {
    set ::g(1) [page_get $::p1 1]
  } msg]
  if {$v} {lappend v $msg}
  set v
} {0}
do_test pager2-3.4 {
  page_read $::g(1)
} {Page-One}
do_test pager2-3.5 {
  for {set i 2} {$i<=20} {incr i} {
    set gx [page_get $::p1 $i]
    page_write $gx "Page-$i"
    page_unref $gx
  }
  pager_commit $::p1
} {}
for {set i 2} {$i<=20} {incr i} {
  do_test pager2-3.6.[expr {$i-1}] [subst {
    set gx \[page_get $::p1 $i\]
    set v \[page_read \$gx\]
    page_unref \$gx
    set v
  }] "Page-$i"
}
for {set i 1} {$i<=20} {incr i} {
  regsub -all CNT {
    set ::g1 [page_get $::p1 CNT]
    set ::g2 [page_get $::p1 CNT]
    set ::vx [page_read $::g2]
    expr {$::g1==$::g2}
  } $i body;
  do_test pager2-3.7.$i.1 $body {1}
  regsub -all CNT {
    page_unref $::g2
    set vy [page_read $::g1]
    expr {$vy==$::vx}
  } $i body;
  do_test pager2-3.7.$i.2 $body {1}
  regsub -all CNT {
    page_unref $::g1
    set gx [page_get $::p1 CNT]
    set vy [page_read $gx]
    page_unref $gx
    expr {$vy==$::vx}
  } $i body;
  do_test pager2-3.7.$i.3 $body {1}
}
do_test pager2-3.99 {
  pager_close $::p1
} {}

# tests of the checkpoint mechanism and api
#
do_test pager2-4.0 {
  set v [catch {
    set ::p1 [pager_open :memory: 15]
  } msg]
  if {$v} {lappend v $msg}
  set v
} {0}
do_test pager2-4.1 {
  set g1 [page_get $::p1 1]
  page_write $g1 "Page-1 v0"
  for {set i 2} {$i<=20} {incr i} {
    set gx [page_get $::p1 $i]
    page_write $gx "Page-$i v0"
    page_unref $gx
  }
  pager_commit $::p1
} {}
for {set i 1} {$i<=20} {incr i} {
  do_test pager2-4.2.$i {
    set gx [page_get $p1 $i]
    set v [page_read $gx]
    page_unref $gx
    set v
  } "Page-$i v0"
}
do_test pager2-4.3 {
  lrange [pager_stats $::p1] 0 1
} {ref 1}
do_test pager2-4.4 {
  lrange [pager_stats $::p1] 8 9
} {state 1}

for {set i 1} {$i<20} {incr i} {
  do_test pager2-4.5.$i.0 {
    set res {}
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      set shouldbe "Page-$j v[expr {$i-1}]"
      if {$value!=$shouldbe} {
        lappend res $value $shouldbe
      }
    }
    set res
  } {}
  do_test pager2-4.5.$i.1 {
    page_write $g1 "Page-1 v$i"
    lrange [pager_stats $p1] 8 9
  } {state 2}
  do_test pager2-4.5.$i.2 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_stmt_begin $p1
      }
    }
  } {}
  do_test pager2-4.5.$i.3 {
    set res {}
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      set shouldbe "Page-$j v$i"
      if {$value!=$shouldbe} {
        lappend res $value $shouldbe
      }
    }
    set res
  } {}
  do_test pager2-4.5.$i.4 {
    pager_rollback $p1
    set res {}
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      set shouldbe "Page-$j v[expr {$i-1}]"
      if {$value!=$shouldbe} {
        lappend res $value $shouldbe
      }
    }
    set res
  } {}
  do_test pager2-4.5.$i.5 {
    page_write $g1 "Page-1 v$i"
    lrange [pager_stats $p1] 8 9
  } {state 2}
  do_test pager2-4.5.$i.6 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_stmt_begin $p1
      }
    }
  } {}
  do_test pager2-4.5.$i.7 {
    pager_stmt_rollback $p1
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      if {$j<=$i || $i==1} {
        set shouldbe "Page-$j v$i"
      } else {
        set shouldbe "Page-$j v[expr {$i-1}]"
      }
      if {$value!=$shouldbe} {
        lappend res $value $shouldbe
      }
    }
    set res
  } {}
  do_test pager2-4.5.$i.8 {
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      page_write $gx "Page-$j v$i"
      page_unref $gx
      if {$j==$i} {
        pager_stmt_begin $p1
      }
    }
  } {}
  do_test pager2-4.5.$i.9 {
    pager_stmt_commit $p1
    for {set j 2} {$j<=20} {incr j} {
      set gx [page_get $p1 $j]
      set value [page_read $gx]
      page_unref $gx
      set shouldbe "Page-$j v$i"
      if {$value!=$shouldbe} {
        lappend res $value $shouldbe
      }
    }
    set res
  } {}
  do_test pager2-4.5.$i.10 {
    pager_commit $p1
    lrange [pager_stats $p1] 8 9
  } {state 1}
}

do_test pager2-4.99 {
  pager_close $::p1
} {}

} ;# end if( not mem: and has pager_open command );


finish_test