rc = sqlite3PagerPagecount(pPager, &dummy);
  }
  pPager->state = PAGER_SHARED;

  return rc;
}

/*
** Check for the existence of or delete the *-wal file that corresponds to
** the database opened by pPager.
**
** When pExists!=NULL, set *pExists to 1 if the *-wal file exists, or 0
** if the *-wal file does not exist.
**
** When pExists==NULL, delete the *-wal file if it exists, or the do
** nothing if the *-wal file does not exist.
**
** Return SQLITE_OK on success. If on an IO or OOM error occurs, return
** an SQLite error code.
*/
static int pagerCheckForOrDeleteWAL(Pager *pPager, int *pExists){
  int rc;                         /* Return code */
  char *zWal = pPager->zWal;      /* Name of the WAL file */

  assert( !pPager->tempFile );
  if( pExists ){
    rc = sqlite3OsAccess(pPager->pVfs, zWal, SQLITE_ACCESS_EXISTS, pExists);
  }else{
    rc = sqlite3OsDelete(pPager->pVfs, zWal, 0);
  }
  return rc;
}

/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists if the database is not empy, or verify that the *-wal file does
** not exist (by deleting it) if the database file is empty.
**
** If the database is not empty and the *-wal file exists, open the pager
** in WAL mode.  If the database is empty or if no *-wal file exists and
................................................................................
  if( !pPager->tempFile ){
    int isWal;                    /* True if WAL file exists */
    int nPage;                    /* Size of the database file */
    assert( pPager->state>=SHARED_LOCK );
    rc = sqlite3PagerPagecount(pPager, &nPage);
    if( rc ) return rc;
    if( nPage==0 ){
      rc = pagerCheckForOrDeleteWAL(pPager, 0);
      isWal = 0;
    }else{
      rc = pagerCheckForOrDeleteWAL(pPager, &isWal);


    }
    if( rc==SQLITE_OK ){
      if( isWal ){
        pager_reset(pPager);
        rc = sqlite3PagerOpenWal(pPager, 0);
        if( rc==SQLITE_OK ){
          rc = pagerBeginReadTransaction(pPager);
................................................................................
  if( !pPager->tempFile && !pPager->pWal ){
    if( !sqlite3PagerWalSupported(pPager) ) return SQLITE_CANTOPEN;

    /* Open the connection to the log file. If this operation fails, 
    ** (e.g. due to malloc() failure), unlock the database file and 
    ** return an error code.
    */
    rc = sqlite3WalOpen(pPager->pVfs, pPager->fd,
                        pPager->zWal, &pPager->pWal);
    if( rc==SQLITE_OK ){
      pPager->journalMode = PAGER_JOURNALMODE_WAL;
    }
  }else{
    *pisOpen = 1;
  }

................................................................................
  ** it may need to be checkpointed before the connection can switch to
  ** rollback mode. Open it now so this can happen.
  */
  if( !pPager->pWal ){
    int logexists = 0;
    rc = sqlite3OsLock(pPager->fd, SQLITE_LOCK_SHARED);
    if( rc==SQLITE_OK ){
      rc = pagerCheckForOrDeleteWAL(pPager, &logexists);


    }
    if( rc==SQLITE_OK && logexists ){
      rc = sqlite3WalOpen(pPager->pVfs, pPager->fd,
                          pPager->zWal, &pPager->pWal);
    }
  }
    

    rc = sqlite3PagerPagecount(pPager, &dummy);
  }
  pPager->state = PAGER_SHARED;

  return rc;
}



























/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists if the database is not empy, or verify that the *-wal file does
** not exist (by deleting it) if the database file is empty.
**
** If the database is not empty and the *-wal file exists, open the pager
** in WAL mode.  If the database is empty or if no *-wal file exists and
................................................................................
  if( !pPager->tempFile ){
    int isWal;                    /* True if WAL file exists */
    int nPage;                    /* Size of the database file */
    assert( pPager->state>=SHARED_LOCK );
    rc = sqlite3PagerPagecount(pPager, &nPage);
    if( rc ) return rc;
    if( nPage==0 ){
      rc = sqlite3OsDelete(pPager->pVfs, pPager->zWal, 0);
      isWal = 0;
    }else{
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &isWal
      );
    }
    if( rc==SQLITE_OK ){
      if( isWal ){
        pager_reset(pPager);
        rc = sqlite3PagerOpenWal(pPager, 0);
        if( rc==SQLITE_OK ){
          rc = pagerBeginReadTransaction(pPager);
................................................................................
  if( !pPager->tempFile && !pPager->pWal ){
    if( !sqlite3PagerWalSupported(pPager) ) return SQLITE_CANTOPEN;

    /* Open the connection to the log file. If this operation fails, 
    ** (e.g. due to malloc() failure), unlock the database file and 
    ** return an error code.
    */
    rc = sqlite3WalOpen(pPager->pVfs, pPager->fd, pPager->zWal, &pPager->pWal);

    if( rc==SQLITE_OK ){
      pPager->journalMode = PAGER_JOURNALMODE_WAL;
    }
  }else{
    *pisOpen = 1;
  }

................................................................................
  ** it may need to be checkpointed before the connection can switch to
  ** rollback mode. Open it now so this can happen.
  */
  if( !pPager->pWal ){
    int logexists = 0;
    rc = sqlite3OsLock(pPager->fd, SQLITE_LOCK_SHARED);
    if( rc==SQLITE_OK ){
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &logexists
      );
    }
    if( rc==SQLITE_OK && logexists ){
      rc = sqlite3WalOpen(pPager->pVfs, pPager->fd,
                          pPager->zWal, &pPager->pWal);
    }
  }