SQLite

  ** either SQLITE_IOERR or SQLITE_FULL during rollback or while finalizing 
  ** a journal file. (although the in-memory journal implementation may 
  ** return SQLITE_IOERR_NOMEM while the journal file is being written). It 
  ** is therefore not possible for an in-memory pager to enter the ERROR 
  ** state.
  */
  if( MEMDB ){
    assert( !isOpen(p->fd) );
    assert( p->noSync );
    assert( p->journalMode==PAGER_JOURNALMODE_OFF 
         || p->journalMode==PAGER_JOURNALMODE_MEMORY 
    );
    assert( p->eState!=PAGER_ERROR && p->eState!=PAGER_OPEN );
    assert( pagerUseWal(p)==0 );
  }

  ** function returns zero if the WAL is not open (i.e. Pager.pWal==0), or
  ** if the database size is not available. The database size is not
  ** available from the WAL sub-system if the log file is empty or
  ** contains no valid committed transactions.
  */
  assert( pPager->eState==PAGER_OPEN );
  assert( pPager->eLock>=SHARED_LOCK );
  assert( isOpen(pPager->fd) );
  assert( pPager->tempFile==0 );
  nPage = sqlite3WalDbsize(pPager->pWal);

  /* If the number of pages in the database is not available from the
  ** WAL sub-system, determine the page counte based on the size of
  ** the database file.  If the size of the database file is not an
  ** integer multiple of the page-size, round up the result.
  */
  if( nPage==0 && ALWAYS(isOpen(pPager->fd)) ){
    i64 n = 0;                    /* Size of db file in bytes */


    int rc = sqlite3OsFileSize(pPager->fd, &n);
    if( rc!=SQLITE_OK ){
      return rc;

    }
    nPage = (Pgno)((n+pPager->pageSize-1) / pPager->pageSize);
  }

  /* If the current number of pages in the file is greater than the
  ** configured maximum pager number, increase the allowed limit so
  ** that the file can be read.

    ** in fact there is none.  This results in a false-positive which will
    ** be dealt with by the playback routine.  Ticket #3883.
    */
    rc = sqlite3OsCheckReservedLock(pPager->fd, &locked);
    if( rc==SQLITE_OK && !locked ){
      Pgno nPage;                 /* Number of pages in database file */

      assert( pPager->tempFile==0 );
      rc = pagerPagecount(pPager, &nPage);
      if( rc==SQLITE_OK ){
        /* If the database is zero pages in size, that means that either (1) the
        ** journal is a remnant from a prior database with the same name where
        ** the database file but not the journal was deleted, or (2) the initial
        ** transaction that populates a new database is being rolled back.
        ** In either case, the journal file can be deleted.  However, take care

    /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
    ** number greater than this, or the unused locking-page, is requested. */
    if( pgno>PAGER_MAX_PGNO || pgno==PAGER_MJ_PGNO(pPager) ){
      rc = SQLITE_CORRUPT_BKPT;
      goto pager_acquire_err;
    }

    assert( !isOpen(pPager->fd) || !MEMDB );
    if( !isOpen(pPager->fd) || pPager->dbSize<pgno || noContent ){
      if( pgno>pPager->mxPgno ){
        rc = SQLITE_FULL;
        goto pager_acquire_err;
      }
      if( noContent ){
        /* Failure to set the bits in the InJournal bit-vectors is benign.
        ** It merely means that we might do some extra work to journal a