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Overview
Comment:Fixes for error handling with temp databases. And for errors that occur within OS locking primitives.
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SHA1:f99a902f9b3d0bf6f607c4ba641b4096fbbef5d5
User & Date: dan 2010-08-05 15:30:22
Context
2010-08-05
16:08
Catch an error code that was not being propagated back to the caller. check-in: 800f4969 user: dan tags: experimental
15:30
Fixes for error handling with temp databases. And for errors that occur within OS locking primitives. check-in: f99a902f user: dan tags: experimental
2010-08-04
19:14
Fix some problems with error recovery introduced while reworking pager state. check-in: 77eaab6f user: dan tags: experimental
Changes
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Changes to src/pager.c.

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*/
#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



/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC1(P,D,N,X,E) \
    if( P->xCodec && P->xCodec(P->pCodec,D,N,X)==0 ){ E; }
# define CODEC2(P,D,N,X,E,O) \
................................................................................
  ** on the file.
  */
  assert( pPager->changeCountDone==0 || pPager->eLock>=RESERVED_LOCK );

  switch( p->eState ){
    case PAGER_NONE:
      assert( !MEMDB );
      assert( !p->tempFile );
      assert( pPager->errCode==SQLITE_OK );
      assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
      break;

    case PAGER_READER:
      assert( pPager->errCode==SQLITE_OK );

      assert( p->eLock>=SHARED_LOCK || p->noReadlock );
      break;

    case PAGER_WRITER_INITIAL:

      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        assert( p->eLock>=RESERVED_LOCK );
      }
      assert( pPager->dbSize==pPager->dbOrigSize );
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->setMaster==0 );
      break;

    case PAGER_WRITER_CACHEMOD:

      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        /* It is possible that if journal_mode=wal here that neither the
        ** journal file nor the WAL file are open. This happens during
        ** a rollback transaction that switches from journal_mode=off
        ** to journal_mode=wal.
        */
................................................................................
             || p->journalMode==PAGER_JOURNALMODE_WAL 
        );
      }
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      break;

    case PAGER_WRITER_DBMOD:

      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );
      assert( p->eLock>=EXCLUSIVE_LOCK || pagerUseWal(pPager) );
      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      break;

    case PAGER_WRITER_FINISHED:

      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );
      assert( p->eLock>=EXCLUSIVE_LOCK || pagerUseWal(pPager) );
      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      break;

    case PAGER_ERROR:
................................................................................
/*
** (gdb) printf "%s", print_pager_state(pPager)
*/
static char *print_pager_state(Pager *p){
  static char zRet[1024];

  sqlite3_snprintf(1024, zRet,
      "State:         %s\n"
      "Lock:          %s\n"
      "Locking mode:  locking_mode=%s\n"
      "Journal mode:  journal_mode=%s\n"
      "Backing store: tempFile=%d memDb=%d useJournal=%d\n"

      , p->eState==PAGER_NONE            ? "NONE" :
        p->eState==PAGER_READER          ? "READER" :
        p->eState==PAGER_WRITER_INITIAL  ? "WRITER_INITIAL" :
        p->eState==PAGER_WRITER_CACHEMOD ? "WRITER_CACHEMOD" :
        p->eState==PAGER_WRITER_DBMOD    ? "WRITER_DBMOD" :
        p->eState==PAGER_WRITER_FINISHED ? "WRITER_FINISHED" :
        p->eState==PAGER_ERROR           ? "ERROR" : "?error?"

      , p->eLock==NO_LOCK         ? "NONE" :
        p->eLock==RESERVED_LOCK   ? "RESERVED" :
        p->eLock==EXCLUSIVE_LOCK  ? "EXCLUSIVE" :
        p->eLock==SHARED_LOCK     ? "SHARED" : "?error?"

      , p->exclusiveMode ? "exclusive" : "normal"
      , p->journalMode==PAGER_JOURNALMODE_MEMORY   ? "memory" :
        p->journalMode==PAGER_JOURNALMODE_OFF      ? "off" :
        p->journalMode==PAGER_JOURNALMODE_DELETE   ? "delete" :
        p->journalMode==PAGER_JOURNALMODE_PERSIST  ? "persist" :
        p->journalMode==PAGER_JOURNALMODE_TRUNCATE ? "truncate" :
        p->journalMode==PAGER_JOURNALMODE_WAL      ? "wal" : "?error?"
      , (int)p->tempFile, (int)p->memDb, (int)p->useJournal

  );

  return zRet;
}
#endif

/*
................................................................................
static int write32bits(sqlite3_file *fd, i64 offset, u32 val){
  char ac[4];
  put32bits(ac, val);
  return sqlite3OsWrite(fd, ac, 4, offset);
}

/*
** If file pFd is open, call sqlite3OsUnlock() on it.


*/
static int osUnlock(Pager *pPager, int eLock){
  int rc = SQLITE_OK;

  if( isOpen(pPager->fd) ){
    assert( pPager->eLock>=eLock );
    assert( eLock!=NO_LOCK || pagerUseWal(pPager)==0 );
    rc = sqlite3OsUnlock(pPager->fd, eLock);
    if( rc==SQLITE_OK ){
      pPager->eLock = eLock;
    }

  }
  return rc;
}

static int osLock(Pager *pPager, int eLock){
  int rc;
  assert( eLock==SHARED_LOCK || eLock==RESERVED_LOCK || eLock==EXCLUSIVE_LOCK );
  if( pPager->eLock>=eLock ){
    rc = SQLITE_OK;
  }else{
    rc = sqlite3OsLock(pPager->fd, eLock);
    if( rc==SQLITE_OK ){
      pPager->eLock = eLock;
      IOTRACE(("LOCK %p %d\n", pPager, locktype))
    }
  }
  return rc;
}

/*
** This function determines whether or not the atomic-write optimization
................................................................................
  releaseAllSavepoints(pPager);

  if( pagerUseWal(pPager) ){
    assert( !isOpen(pPager->jfd) );
    sqlite3WalEndReadTransaction(pPager->pWal);
    pPager->eState = PAGER_NONE;
  }else if( !pPager->exclusiveMode ){

    int iDc = isOpen(pPager->fd)?sqlite3OsDeviceCharacteristics(pPager->fd):0;

    /* If the operating system support deletion of open files, then
    ** close the journal file when dropping the database lock.  Otherwise
    ** another connection with journal_mode=delete might delete the file
    ** out from under us.
    */
................................................................................
    assert( (PAGER_JOURNALMODE_TRUNCATE & 5)==1 );
    assert( (PAGER_JOURNALMODE_PERSIST  & 5)==1 );
    if( 0==(iDc & SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN)
     || 1!=(pPager->journalMode & 5)
    ){
      sqlite3OsClose(pPager->jfd);
    }

    osUnlock(pPager, NO_LOCK);




    /* The pager state may be changed from PAGER_ERROR to PAGER_NONE here
    ** without clearing the error code. This is intentional - the error
    ** code is cleared and the cache reset in the block below.
    */
    assert( pPager->errCode || pPager->eState!=PAGER_ERROR );
    pPager->changeCountDone = 0;
    pPager->eState = PAGER_NONE;
    IOTRACE(("UNLOCK %p\n", pPager))
  }

  /* If Pager.errCode is set, the contents of the pager cache cannot be
  ** trusted. Now that there are no outstanding references to the pager,
  ** it can safely move back to PAGER_NONE state. This happens in both
  ** normal and exclusive-locking mode.
  */
  if( pPager->errCode && !pPager->tempFile ){
    pager_reset(pPager);
    pPager->changeCountDone = 0;
    pPager->eState = PAGER_NONE;
    pPager->errCode = SQLITE_OK;
  }




}

/*
** This function should be called when an IOERR, CORRUPT or FULL error
** may have occurred. 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 
................................................................................
    */
    rc2 = sqlite3WalEndWriteTransaction(pPager->pWal);
    assert( rc2==SQLITE_OK );
  }
  if( !pPager->exclusiveMode 
   && (!pagerUseWal(pPager) || sqlite3WalExclusiveMode(pPager->pWal, 0))
  ){
    rc2 = osUnlock(pPager, SHARED_LOCK);
    pPager->changeCountDone = 0;
  }
  pPager->eState = PAGER_READER;
  pPager->setMaster = 0;

  return (rc==SQLITE_OK?rc2:rc);
}
................................................................................

  /* If this page has already been played by before during the current
  ** rollback, then don't bother to play it back again.
  */
  if( pDone && (rc = sqlite3BitvecSet(pDone, pgno))!=SQLITE_OK ){
    return rc;
  }
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD );



  /* When playing back page 1, restore the nReserve setting
  */
  if( pgno==1 && pPager->nReserve!=((u8*)aData)[20] ){
    pPager->nReserve = ((u8*)aData)[20];
    pagerReportSize(pPager);
  }
................................................................................
           (isMainJrnl?"main-journal":"sub-journal")
  ));
  if( isMainJrnl ){
    isSynced = pPager->noSync || (*pOffset <= pPager->journalHdr);
  }else{
    isSynced = (pPg==0 || 0==(pPg->flags & PGHDR_NEED_SYNC));
  }
  if( (pPager->eState>=PAGER_WRITER_DBMOD)
   && isOpen(pPager->fd)
   && isSynced
  ){
    i64 ofst = (pgno-1)*(i64)pPager->pageSize;
    testcase( !isSavepnt && pPg!=0 && (pPg->flags&PGHDR_NEED_SYNC)!=0 );
    assert( !pagerUseWal(pPager) );
    rc = sqlite3OsWrite(pPager->fd, (u8*)aData, pPager->pageSize, ofst);
................................................................................
**
** If successful, return SQLITE_OK. If an IO error occurs while modifying
** the database file, return the error code to the caller.
*/
static int pager_truncate(Pager *pPager, Pgno nPage){
  int rc = SQLITE_OK;
  assert( pPager->eState!=PAGER_ERROR );



  if( pPager->eState>=PAGER_WRITER_DBMOD && isOpen(pPager->fd) ){

    i64 currentSize, newSize;
    /* TODO: Is it safe to use Pager.dbFileSize here? */
    rc = sqlite3OsFileSize(pPager->fd, &currentSize);
    newSize = pPager->pageSize*(i64)nPage;
    if( rc==SQLITE_OK && currentSize!=newSize ){
      if( currentSize>newSize ){
        rc = sqlite3OsTruncate(pPager->fd, newSize);
................................................................................
    }else{
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &isWal
      );
    }
    if( rc==SQLITE_OK ){
      if( isWal ){
        assert( sqlite3PcachePagecount(pPager->pPCache)==0 );
        rc = sqlite3PagerOpenWal(pPager, 0);
        if( rc==SQLITE_OK ){
          rc = pagerBeginReadTransaction(pPager);
        }
      }else if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
        pPager->journalMode = PAGER_JOURNALMODE_DELETE;
      }
................................................................................
        rc = sqlite3OsFileSize(pPager->fd, &nByte);
        if( rc!=SQLITE_OK ) return rc;
      }
      pNew = (char *)sqlite3PageMalloc(pageSize);
      if( !pNew ){
        rc = SQLITE_NOMEM;
      }else{
        assert( pPager->eState==PAGER_NONE || pPager->eState==PAGER_READER );
        pager_reset(pPager);
        pPager->dbSize = nByte/pageSize;
        pPager->pageSize = pageSize;
        sqlite3PageFree(pPager->pTmpSpace);
        pPager->pTmpSpace = pNew;
        sqlite3PcacheSetPageSize(pPager->pPCache, pageSize);
      }
................................................................................
  ** sqlite3PagerSetBusyhandler().
  */
  assert( (pPager->eLock>=locktype)
       || (pPager->eLock==NO_LOCK && locktype==SHARED_LOCK)
       || (pPager->eLock==RESERVED_LOCK && locktype==EXCLUSIVE_LOCK)
  );

  if( pPager->eLock>=locktype ){
    rc = SQLITE_OK;
  }else{
    do {
      rc = osLock(pPager, locktype);
    }while( rc==SQLITE_BUSY && pPager->xBusyHandler(pPager->pBusyHandlerArg) );
  }
  return rc;
}

/*
** Function assertTruncateConstraint(pPager) checks that one of the 
** following is true for all dirty pages currently in the page-cache:
**
................................................................................
      ** a RESERVED lock to avoid race conditions and to avoid violating
      ** [H33020].
      */
      rc = pagerPagecount(pPager, &nPage);
      if( rc==SQLITE_OK ){
        if( nPage==0 ){
          sqlite3BeginBenignMalloc();
          if( osLock(pPager, RESERVED_LOCK)==SQLITE_OK ){
            sqlite3OsDelete(pVfs, pPager->zJournal, 0);
            osUnlock(pPager, SHARED_LOCK);
          }
          sqlite3EndBenignMalloc();
        }else{
          /* The journal file exists and no other connection has a reserved
          ** or greater lock on the database file. Now check that there is
          ** at least one non-zero bytes at the start of the journal file.
          ** If there is, then we consider this journal to be hot. If not, 
................................................................................

  /* This routine is only called from b-tree and only when there are no
  ** outstanding pages. This implies that the pager state should either
  ** be NONE or READER. READER is only possible if the pager is or was in 
  ** exclusive access mode.
  */
  assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
  assert( pPager->eState==PAGER_NONE || pPager->eState==PAGER_READER );
  assert( assert_pager_state(pPager) );

  if( NEVER(MEMDB && pPager->errCode) ){ return pPager->errCode; }

  if( !pagerUseWal(pPager) && pPager->eState==PAGER_NONE ){
    int bHotJournal = 1;          /* True if there exists a hot journal-file */

    assert( !MEMDB && !pPager->tempFile );
    assert( pPager->noReadlock==0 || pPager->readOnly );

    if( pPager->noReadlock==0 ){
      rc = pager_wait_on_lock(pPager, SHARED_LOCK);
      if( rc!=SQLITE_OK ){
        assert( pPager->eLock==PAGER_UNLOCK );
        goto failed;
................................................................................
      ** other process attempting to access the database file will get to 
      ** this point in the code and fail to obtain its own EXCLUSIVE lock 
      ** on the database file.
      **
      ** Unless the pager is in locking_mode=exclusive mode, the lock is
      ** downgraded to SHARED_LOCK before this function returns.
      */
      rc = osLock(pPager, EXCLUSIVE_LOCK);
      if( rc!=SQLITE_OK ){
        goto failed;
      }
 
      /* If it is not already open and the file exists on disk, open the 
      ** journal for read/write access. Write access is required because 
      ** in exclusive-access mode the file descriptor will be kept open 
................................................................................
          assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
          if( rc==SQLITE_OK && fout&SQLITE_OPEN_READONLY ){
            rc = SQLITE_CANTOPEN_BKPT;
            sqlite3OsClose(pPager->jfd);
          }
        }
      }
      if( rc!=SQLITE_OK ){
        goto failed;
      }

      /* Reset the journal status fields to indicates that we have no
      ** rollback journal at this time. */
      pPager->journalOff = 0;
      pPager->setMaster = 0;
      pPager->journalHdr = 0;
 
      /* Make sure the journal file has been synced to disk. */
 
      /* Playback and delete the journal.  Drop the database write
      ** lock and reacquire the read lock. Purge the cache before
      ** playing back the hot-journal so that we don't end up with
      ** an inconsistent cache.  Sync the hot journal before playing
      ** it back since the process that crashed and left the hot journal
      ** probably did not sync it and we are required to always sync
      ** the journal before playing it back.
      **
      ** Even if an error occurs while syncing or rolling back the 
      ** hot-journal, there is no need to enter the ERROR state here, as
      ** the pager never left state NONE anyhow.
      */
      if( isOpen(pPager->jfd) ){

        rc = pagerSyncHotJournal(pPager);
        if( rc==SQLITE_OK ){
          assert( pPager->eState==PAGER_NONE );
          pPager->eState = PAGER_WRITER_FINISHED;
          rc = pager_playback(pPager, 1);
          pPager->eState = PAGER_NONE;
        }




        if( rc!=SQLITE_OK ){

          goto failed;
        }
      }else{
        osUnlock(pPager, SHARED_LOCK);
      }

      assert( pPager->eState==PAGER_NONE );
      assert( (pPager->eLock==SHARED_LOCK)
           || (pPager->exclusiveMode && pPager->eLock>SHARED_LOCK)
      );
    }


    if( pPager->pBackup || sqlite3PcachePagecount(pPager->pPCache)>0 ){

      /* 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
................................................................................
    assert( pPager->pInJournal==0 );

    if( pagerUseWal(pPager) ){
      /* If the pager is configured to use locking_mode=exclusive, and an
      ** exclusive lock on the database is not already held, obtain it now.
      */
      if( pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, -1) ){
        rc = osLock(pPager, EXCLUSIVE_LOCK);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        sqlite3WalExclusiveMode(pPager->pWal, 1);
      }

      /* Grab the write lock on the log file. If successful, upgrade to
................................................................................
      rc = sqlite3WalBeginWriteTransaction(pPager->pWal);
    }else{
      /* Obtain a RESERVED lock on the database file. If the exFlag parameter
      ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
      ** busy-handler callback can be used when upgrading to the EXCLUSIVE
      ** lock, but not when obtaining the RESERVED lock.
      */
      rc = osLock(pPager, RESERVED_LOCK);
      if( rc==SQLITE_OK && exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }


    if( rc==SQLITE_OK ){
................................................................................
** then savepoint iSavepoint is also destroyed.
**
** This function may return SQLITE_NOMEM if a memory allocation fails,
** or an IO error code if an IO error occurs while rolling back a 
** savepoint. If no errors occur, SQLITE_OK is returned.
*/ 
int sqlite3PagerSavepoint(Pager *pPager, int op, int iSavepoint){
  int rc = SQLITE_OK;

  assert( op==SAVEPOINT_RELEASE || op==SAVEPOINT_ROLLBACK );
  assert( iSavepoint>=0 || op==SAVEPOINT_ROLLBACK );

  if( iSavepoint<pPager->nSavepoint ){
    int ii;            /* Iterator variable */
    int nNew;          /* Number of remaining savepoints after this op. */

    /* Figure out how many savepoints will still be active after this
    ** operation. Store this value in nNew. Then free resources associated 
    ** with any savepoints that are destroyed by this operation.
    */
................................................................................
    ** the database file, so the playback operation can be skipped.
    */
    else if( pagerUseWal(pPager) || isOpen(pPager->jfd) ){
      PagerSavepoint *pSavepoint = (nNew==0)?0:&pPager->aSavepoint[nNew-1];
      rc = pagerPlaybackSavepoint(pPager, pSavepoint);
      assert(rc!=SQLITE_DONE);
    }
  
  }
  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlite3PagerFilename(Pager *pPager){
................................................................................
      sqlite3PcacheDrop(pPgOld);
    }
  }

  origPgno = pPg->pgno;
  sqlite3PcacheMove(pPg, pgno);
  sqlite3PcacheMakeDirty(pPg);











  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 
    ** "is journaled" bitvec flag has been set. This needs to be remedied by
    ** loading the page into the pager-cache and setting the PGHDR_NEED_SYNC
................................................................................
      return rc;
    }
    pPgHdr->flags |= PGHDR_NEED_SYNC;
    sqlite3PcacheMakeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }

  /*
  ** For an in-memory database, make sure the original page continues
  ** to exist, in case the transaction needs to roll back.  Use pPgOld
  ** as the original page since it has already been allocated.
  */
  if( MEMDB ){
    sqlite3PcacheMove(pPgOld, origPgno);
    sqlite3PagerUnref(pPgOld);
  }

  return SQLITE_OK;
}
#endif

/*
** Return a pointer to the data for the specified page.
*/
................................................................................
    assert( eOld==PAGER_JOURNALMODE_MEMORY || eOld==PAGER_JOURNALMODE_OFF );
    if( eMode!=PAGER_JOURNALMODE_MEMORY && eMode!=PAGER_JOURNALMODE_OFF ){
      eMode = eOld;
    }
  }

  if( eMode!=eOld ){
    /* When changing between rollback modes, close the journal file prior
    ** to the change.  But when changing from a rollback mode to WAL, keep
    ** the journal open since there is a rollback-style transaction in play
    ** used to convert the version numbers in the btree header.
    */
    if( isOpen(pPager->jfd) && eMode!=PAGER_JOURNALMODE_WAL ){
      sqlite3OsClose(pPager->jfd);
    }

    /* Change the journal mode. */
    pPager->journalMode = (u8)eMode;

    /* When transistioning from TRUNCATE or PERSIST to any other journal
    ** mode except WAL (and we are not in locking_mode=EXCLUSIVE) then 
    ** delete the journal file.
................................................................................
    assert( (PAGER_JOURNALMODE_DELETE & 5)==0 );
    assert( (PAGER_JOURNALMODE_MEMORY & 5)==4 );
    assert( (PAGER_JOURNALMODE_OFF & 5)==0 );
    assert( (PAGER_JOURNALMODE_WAL & 5)==5 );

    assert( isOpen(pPager->fd) || pPager->exclusiveMode );
    if( !pPager->exclusiveMode && (eOld & 5)==1 && (eMode & 1)==0 ){



      /* In this case we would like to delete the journal file. If it is
      ** not possible, then that is not a problem. Deleting the journal file
      ** here is an optimization only.
      **
      ** Before deleting the journal file, obtain a RESERVED lock on the
      ** database file. This ensures that the journal file is not deleted
................................................................................
      int rc = SQLITE_OK;
      int state = pPager->eState;
      if( state==PAGER_NONE ){
        rc = sqlite3PagerSharedLock(pPager);
      }
      if( pPager->eState==PAGER_READER ){
        assert( rc==SQLITE_OK );
        rc = osLock(pPager, RESERVED_LOCK);
      }
      if( rc==SQLITE_OK ){
        sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }
      if( rc==SQLITE_OK && state==PAGER_READER ){
        osUnlock(pPager, SHARED_LOCK);
      }else if( state==PAGER_NONE ){
        pager_unlock(pPager);
      }
      assert( state==pPager->eState );
    }
  }

................................................................................

/*
** Return TRUE if the pager is in a state where it is OK to change the
** journalmode.  Journalmode changes can only happen when the database
** is unmodified.
*/
int sqlite3PagerOkToChangeJournalMode(Pager *pPager){

  if( pPager->eState>=PAGER_WRITER_CACHEMOD ) return 0;
  if( NEVER(isOpen(pPager->jfd) && pPager->journalOff>0) ) return 0;
  return 1;
}

/*
** Get/set the size-limit used for persistent journal files.
................................................................................
  assert( pPager->eState==PAGER_NONE   || pbOpen );
  assert( pPager->eState==PAGER_READER || !pbOpen );
  assert( pbOpen==0 || *pbOpen==0 );
  assert( pbOpen!=0 || (!pPager->tempFile && !pPager->pWal) );

  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 ){
................................................................................

  /* If the log file is not already open, but does exist in the file-system,
  ** 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 = osLock(pPager, SHARED_LOCK);
    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,
................................................................................
    }
  }
    
  /* Checkpoint and close the log. Because an EXCLUSIVE lock is held on
  ** the database file, the log and log-summary files will be deleted.
  */
  if( rc==SQLITE_OK && pPager->pWal ){
    rc = osLock(pPager, EXCLUSIVE_LOCK);
    if( rc==SQLITE_OK ){
      rc = sqlite3WalClose(pPager->pWal,
                           (pPager->noSync ? 0 : pPager->sync_flags), 
        pPager->pageSize, (u8*)pPager->pTmpSpace
      );
      pPager->pWal = 0;
    }else{
      /* If we cannot get an EXCLUSIVE lock, downgrade the PENDING lock
      ** that we did get back to SHARED. */
      osUnlock(pPager, SQLITE_LOCK_SHARED);
    }
  }
  return rc;
}

#ifdef SQLITE_HAS_CODEC
/*







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341
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...
719
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721
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723
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725

726
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729
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733
734
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...
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764
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768
769
770
771
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773
774
775
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779

780
781
782
783
784
785
786
...
799
800
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802
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804
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806
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808
809
810
811
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815
816
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818
819
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825
826
827
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840
...
895
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899
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903
904
905
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910
911
912
913
914
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926
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928
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930
931
932
933
934
935
936
937
....
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
....
1578
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1593
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1597

1598
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1601
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1607
1608
1609
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1611
1612
1613
1614
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1617
1618
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1620
1621
....
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
....
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
....
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
....
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
....
2840
2841
2842
2843
2844
2845
2846
2847
2848
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2850
2851
2852
2853
2854
....
3167
3168
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3170
3171
3172
3173

3174
3175
3176
3177
3178
3179
3180
....
3319
3320
3321
3322
3323
3324
3325



3326
3327
3328

3329
3330
3331
3332
3333
3334
3335
....
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
....
4406
4407
4408
4409
4410
4411
4412

4413
4414
4415
4416
4417
4418
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4421
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....
4449
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4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
....
4484
4485
4486
4487
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4490











4491
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4499
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4513



4514
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....
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4913
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4915
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4924
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4926
....
4931
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....
5880
5881
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5887
5888
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5893
5894
5895
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....
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....
6097
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....
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6144
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....
6227
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6234
6235
6236
6237
6238
6239
6240
....
6244
6245
6246
6247
6248
6249
6250
6251
6252
6253
6254
6255
6256
6257
6258
6259
....
6262
6263
6264
6265
6266
6267
6268
6269
6270
6271
6272
6273
6274
6275
6276
6277
6278
6279
6280
6281
6282
....
6293
6294
6295
6296
6297
6298
6299
6300
6301
6302
6303
6304
6305
6306
6307
....
6380
6381
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....
6421
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....
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6459
6460
6461
*/
#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

#define UNKNOWN_LOCK      (EXCLUSIVE_LOCK+1)

/*
** A macro used for invoking the codec if there is one
*/
#ifdef SQLITE_HAS_CODEC
# define CODEC1(P,D,N,X,E) \
    if( P->xCodec && P->xCodec(P->pCodec,D,N,X)==0 ){ E; }
# define CODEC2(P,D,N,X,E,O) \
................................................................................
  ** on the file.
  */
  assert( pPager->changeCountDone==0 || pPager->eLock>=RESERVED_LOCK );

  switch( p->eState ){
    case PAGER_NONE:
      assert( !MEMDB );

      assert( pPager->errCode==SQLITE_OK );
      assert( sqlite3PcacheRefCount(pPager->pPCache)==0 || pPager->tempFile );
      break;

    case PAGER_READER:
      assert( pPager->errCode==SQLITE_OK );
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( p->eLock>=SHARED_LOCK || p->noReadlock );
      break;

    case PAGER_WRITER_INITIAL:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        assert( p->eLock>=RESERVED_LOCK );
      }
      assert( pPager->dbSize==pPager->dbOrigSize );
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      assert( pPager->setMaster==0 );
      break;

    case PAGER_WRITER_CACHEMOD:
      assert( p->eLock!=UNKNOWN_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      if( !pagerUseWal(pPager) ){
        /* It is possible that if journal_mode=wal here that neither the
        ** journal file nor the WAL file are open. This happens during
        ** a rollback transaction that switches from journal_mode=off
        ** to journal_mode=wal.
        */
................................................................................
             || p->journalMode==PAGER_JOURNALMODE_WAL 
        );
      }
      assert( pPager->dbOrigSize==pPager->dbFileSize );
      break;

    case PAGER_WRITER_DBMOD:
      assert( p->eLock==EXCLUSIVE_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );
      assert( p->eLock>=EXCLUSIVE_LOCK );
      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      break;

    case PAGER_WRITER_FINISHED:
      assert( p->eLock==EXCLUSIVE_LOCK );
      assert( pPager->errCode==SQLITE_OK );
      assert( !pagerUseWal(pPager) );

      assert( isOpen(p->jfd) 
           || p->journalMode==PAGER_JOURNALMODE_OFF 
           || p->journalMode==PAGER_JOURNALMODE_WAL 
      );
      break;

    case PAGER_ERROR:
................................................................................
/*
** (gdb) printf "%s", print_pager_state(pPager)
*/
static char *print_pager_state(Pager *p){
  static char zRet[1024];

  sqlite3_snprintf(1024, zRet,
      "State:         %s errCode=%d\n"
      "Lock:          %s\n"
      "Locking mode:  locking_mode=%s\n"
      "Journal mode:  journal_mode=%s\n"
      "Backing store: tempFile=%d memDb=%d useJournal=%d\n"
      "Journal:       journalOff=%lld journalHdr=%lld\n"
      , p->eState==PAGER_NONE            ? "NONE" :
        p->eState==PAGER_READER          ? "READER" :
        p->eState==PAGER_WRITER_INITIAL  ? "WRITER_INITIAL" :
        p->eState==PAGER_WRITER_CACHEMOD ? "WRITER_CACHEMOD" :
        p->eState==PAGER_WRITER_DBMOD    ? "WRITER_DBMOD" :
        p->eState==PAGER_WRITER_FINISHED ? "WRITER_FINISHED" :
        p->eState==PAGER_ERROR           ? "ERROR" : "?error?"
      , (int)p->errCode
      , p->eLock==NO_LOCK         ? "NONE" :
        p->eLock==RESERVED_LOCK   ? "RESERVED" :
        p->eLock==EXCLUSIVE_LOCK  ? "EXCLUSIVE" :
        p->eLock==SHARED_LOCK     ? "SHARED" :
        p->eLock==UNKNOWN_LOCK    ? "UNKNOWN" : "?error?"
      , p->exclusiveMode ? "exclusive" : "normal"
      , p->journalMode==PAGER_JOURNALMODE_MEMORY   ? "memory" :
        p->journalMode==PAGER_JOURNALMODE_OFF      ? "off" :
        p->journalMode==PAGER_JOURNALMODE_DELETE   ? "delete" :
        p->journalMode==PAGER_JOURNALMODE_PERSIST  ? "persist" :
        p->journalMode==PAGER_JOURNALMODE_TRUNCATE ? "truncate" :
        p->journalMode==PAGER_JOURNALMODE_WAL      ? "wal" : "?error?"
      , (int)p->tempFile, (int)p->memDb, (int)p->useJournal
      , p->journalOff, p->journalHdr
  );

  return zRet;
}
#endif

/*
................................................................................
static int write32bits(sqlite3_file *fd, i64 offset, u32 val){
  char ac[4];
  put32bits(ac, val);
  return sqlite3OsWrite(fd, ac, 4, offset);
}

/*
** This function and pagerLockDb() are wrappers around sqlite3OsLock() and
** sqlite3OsUnlock() that set the Pager.eLock variable to reflect the
** current lock held on the database file.
*/
static int pagerUnlockDb(Pager *pPager, int eLock){
  int rc = SQLITE_OK;
  assert( !pPager->exclusiveMode );
  if( isOpen(pPager->fd) ){
    assert( pPager->eLock>=eLock );
    assert( eLock!=NO_LOCK || pagerUseWal(pPager)==0 );
    rc = sqlite3OsUnlock(pPager->fd, eLock);
    if( pPager->eLock!=UNKNOWN_LOCK ){
      pPager->eLock = eLock;
    }
    IOTRACE(("UNLOCK %p %d\n", pPager, eLock))
  }
  return rc;
}

static int pagerLockDb(Pager *pPager, int eLock){
  int rc;
  assert( eLock==SHARED_LOCK || eLock==RESERVED_LOCK || eLock==EXCLUSIVE_LOCK );
  if( pPager->eLock>=eLock && pPager->eLock!=UNKNOWN_LOCK ){
    rc = SQLITE_OK;
  }else{
    rc = sqlite3OsLock(pPager->fd, eLock);
    if( rc==SQLITE_OK && (pPager->eLock!=UNKNOWN_LOCK||eLock==EXCLUSIVE_LOCK) ){
      pPager->eLock = eLock;
      IOTRACE(("LOCK %p %d\n", pPager, eLock))
    }
  }
  return rc;
}

/*
** This function determines whether or not the atomic-write optimization
................................................................................
  releaseAllSavepoints(pPager);

  if( pagerUseWal(pPager) ){
    assert( !isOpen(pPager->jfd) );
    sqlite3WalEndReadTransaction(pPager->pWal);
    pPager->eState = PAGER_NONE;
  }else if( !pPager->exclusiveMode ){
    int rc;                       /* Error code returned by pagerUnlockDb() */
    int iDc = isOpen(pPager->fd)?sqlite3OsDeviceCharacteristics(pPager->fd):0;

    /* If the operating system support deletion of open files, then
    ** close the journal file when dropping the database lock.  Otherwise
    ** another connection with journal_mode=delete might delete the file
    ** out from under us.
    */
................................................................................
    assert( (PAGER_JOURNALMODE_TRUNCATE & 5)==1 );
    assert( (PAGER_JOURNALMODE_PERSIST  & 5)==1 );
    if( 0==(iDc & SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN)
     || 1!=(pPager->journalMode & 5)
    ){
      sqlite3OsClose(pPager->jfd);
    }

    rc = pagerUnlockDb(pPager, NO_LOCK);
    if( rc!=SQLITE_OK && pPager->eState==PAGER_ERROR ){
      pPager->eLock = UNKNOWN_LOCK;
    }

    /* The pager state may be changed from PAGER_ERROR to PAGER_NONE here
    ** without clearing the error code. This is intentional - the error
    ** code is cleared and the cache reset in the block below.
    */
    assert( pPager->errCode || pPager->eState!=PAGER_ERROR );
    pPager->changeCountDone = 0;
    pPager->eState = PAGER_NONE;

  }

  /* If Pager.errCode is set, the contents of the pager cache cannot be
  ** trusted. Now that there are no outstanding references to the pager,
  ** it can safely move back to PAGER_NONE state. This happens in both
  ** normal and exclusive-locking mode.
  */
  if( pPager->errCode && !MEMDB ){
    pager_reset(pPager);
    pPager->changeCountDone = pPager->tempFile;
    pPager->eState = PAGER_NONE;
    pPager->errCode = SQLITE_OK;
  }

  pPager->journalOff = 0;
  pPager->journalHdr = 0;
  pPager->setMaster = 0;
}

/*
** This function should be called when an IOERR, CORRUPT or FULL error
** may have occurred. 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 
................................................................................
    */
    rc2 = sqlite3WalEndWriteTransaction(pPager->pWal);
    assert( rc2==SQLITE_OK );
  }
  if( !pPager->exclusiveMode 
   && (!pagerUseWal(pPager) || sqlite3WalExclusiveMode(pPager->pWal, 0))
  ){
    rc2 = pagerUnlockDb(pPager, SHARED_LOCK);
    pPager->changeCountDone = 0;
  }
  pPager->eState = PAGER_READER;
  pPager->setMaster = 0;

  return (rc==SQLITE_OK?rc2:rc);
}
................................................................................

  /* If this page has already been played by before during the current
  ** rollback, then don't bother to play it back again.
  */
  if( pDone && (rc = sqlite3BitvecSet(pDone, pgno))!=SQLITE_OK ){
    return rc;
  }
  assert( pPager->eState>=PAGER_WRITER_CACHEMOD 
       || (pPager->eState==PAGER_NONE && isMainJrnl)
  );

  /* When playing back page 1, restore the nReserve setting
  */
  if( pgno==1 && pPager->nReserve!=((u8*)aData)[20] ){
    pPager->nReserve = ((u8*)aData)[20];
    pagerReportSize(pPager);
  }
................................................................................
           (isMainJrnl?"main-journal":"sub-journal")
  ));
  if( isMainJrnl ){
    isSynced = pPager->noSync || (*pOffset <= pPager->journalHdr);
  }else{
    isSynced = (pPg==0 || 0==(pPg->flags & PGHDR_NEED_SYNC));
  }
  if( (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_NONE)
   && isOpen(pPager->fd)
   && isSynced
  ){
    i64 ofst = (pgno-1)*(i64)pPager->pageSize;
    testcase( !isSavepnt && pPg!=0 && (pPg->flags&PGHDR_NEED_SYNC)!=0 );
    assert( !pagerUseWal(pPager) );
    rc = sqlite3OsWrite(pPager->fd, (u8*)aData, pPager->pageSize, ofst);
................................................................................
**
** If successful, return SQLITE_OK. If an IO error occurs while modifying
** the database file, return the error code to the caller.
*/
static int pager_truncate(Pager *pPager, Pgno nPage){
  int rc = SQLITE_OK;
  assert( pPager->eState!=PAGER_ERROR );
  assert( pPager->eState!=PAGER_READER );
  
  if( isOpen(pPager->fd) 
   && (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_NONE) 
  ){
    i64 currentSize, newSize;
    /* TODO: Is it safe to use Pager.dbFileSize here? */
    rc = sqlite3OsFileSize(pPager->fd, &currentSize);
    newSize = pPager->pageSize*(i64)nPage;
    if( rc==SQLITE_OK && currentSize!=newSize ){
      if( currentSize>newSize ){
        rc = sqlite3OsTruncate(pPager->fd, newSize);
................................................................................
    }else{
      rc = sqlite3OsAccess(
          pPager->pVfs, pPager->zWal, SQLITE_ACCESS_EXISTS, &isWal
      );
    }
    if( rc==SQLITE_OK ){
      if( isWal ){
        testcase( sqlite3PcachePagecount(pPager->pPCache)==0 );
        rc = sqlite3PagerOpenWal(pPager, 0);
        if( rc==SQLITE_OK ){
          rc = pagerBeginReadTransaction(pPager);
        }
      }else if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
        pPager->journalMode = PAGER_JOURNALMODE_DELETE;
      }
................................................................................
        rc = sqlite3OsFileSize(pPager->fd, &nByte);
        if( rc!=SQLITE_OK ) return rc;
      }
      pNew = (char *)sqlite3PageMalloc(pageSize);
      if( !pNew ){
        rc = SQLITE_NOMEM;
      }else{

        pager_reset(pPager);
        pPager->dbSize = nByte/pageSize;
        pPager->pageSize = pageSize;
        sqlite3PageFree(pPager->pTmpSpace);
        pPager->pTmpSpace = pNew;
        sqlite3PcacheSetPageSize(pPager->pPCache, pageSize);
      }
................................................................................
  ** sqlite3PagerSetBusyhandler().
  */
  assert( (pPager->eLock>=locktype)
       || (pPager->eLock==NO_LOCK && locktype==SHARED_LOCK)
       || (pPager->eLock==RESERVED_LOCK && locktype==EXCLUSIVE_LOCK)
  );




  do {
    rc = pagerLockDb(pPager, locktype);
  }while( rc==SQLITE_BUSY && pPager->xBusyHandler(pPager->pBusyHandlerArg) );

  return rc;
}

/*
** Function assertTruncateConstraint(pPager) checks that one of the 
** following is true for all dirty pages currently in the page-cache:
**
................................................................................
      ** a RESERVED lock to avoid race conditions and to avoid violating
      ** [H33020].
      */
      rc = pagerPagecount(pPager, &nPage);
      if( rc==SQLITE_OK ){
        if( nPage==0 ){
          sqlite3BeginBenignMalloc();
          if( pagerLockDb(pPager, RESERVED_LOCK)==SQLITE_OK ){
            sqlite3OsDelete(pVfs, pPager->zJournal, 0);
            pagerUnlockDb(pPager, SHARED_LOCK);
          }
          sqlite3EndBenignMalloc();
        }else{
          /* The journal file exists and no other connection has a reserved
          ** or greater lock on the database file. Now check that there is
          ** at least one non-zero bytes at the start of the journal file.
          ** If there is, then we consider this journal to be hot. If not, 
................................................................................

  /* This routine is only called from b-tree and only when there are no
  ** outstanding pages. This implies that the pager state should either
  ** be NONE or READER. READER is only possible if the pager is or was in 
  ** exclusive access mode.
  */
  assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );

  assert( assert_pager_state(pPager) );
  assert( pPager->eState==PAGER_NONE || pPager->eState==PAGER_READER );
  if( NEVER(MEMDB && pPager->errCode) ){ return pPager->errCode; }

  if( !pagerUseWal(pPager) && pPager->eState==PAGER_NONE ){
    int bHotJournal = 1;          /* True if there exists a hot journal-file */

    assert( !MEMDB );
    assert( pPager->noReadlock==0 || pPager->readOnly );

    if( pPager->noReadlock==0 ){
      rc = pager_wait_on_lock(pPager, SHARED_LOCK);
      if( rc!=SQLITE_OK ){
        assert( pPager->eLock==PAGER_UNLOCK );
        goto failed;
................................................................................
      ** other process attempting to access the database file will get to 
      ** this point in the code and fail to obtain its own EXCLUSIVE lock 
      ** on the database file.
      **
      ** Unless the pager is in locking_mode=exclusive mode, the lock is
      ** downgraded to SHARED_LOCK before this function returns.
      */
      rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
      if( rc!=SQLITE_OK ){
        goto failed;
      }
 
      /* If it is not already open and the file exists on disk, open the 
      ** journal for read/write access. Write access is required because 
      ** in exclusive-access mode the file descriptor will be kept open 
................................................................................
          assert( rc!=SQLITE_OK || isOpen(pPager->jfd) );
          if( rc==SQLITE_OK && fout&SQLITE_OPEN_READONLY ){
            rc = SQLITE_CANTOPEN_BKPT;
            sqlite3OsClose(pPager->jfd);
          }
        }
      }











 
      /* Playback and delete the journal.  Drop the database write
      ** lock and reacquire the read lock. Purge the cache before
      ** playing back the hot-journal so that we don't end up with
      ** an inconsistent cache.  Sync the hot journal before playing
      ** it back since the process that crashed and left the hot journal
      ** probably did not sync it and we are required to always sync
      ** the journal before playing it back.




      */
      if( isOpen(pPager->jfd) ){
        assert( rc==SQLITE_OK );
        rc = pagerSyncHotJournal(pPager);
        if( rc==SQLITE_OK ){


          rc = pager_playback(pPager, 1);
          pPager->eState = PAGER_NONE;
        }
      }else if( !pPager->exclusiveMode ){
        pagerUnlockDb(pPager, SHARED_LOCK);
      }

      if( rc!=SQLITE_OK ){
        pager_error(pPager, rc);
        goto failed;



      }

      assert( pPager->eState==PAGER_NONE );
      assert( (pPager->eLock==SHARED_LOCK)
           || (pPager->exclusiveMode && pPager->eLock>SHARED_LOCK)
      );
    }

    if( !pPager->tempFile 
     && (pPager->pBackup || sqlite3PcachePagecount(pPager->pPCache)>0) 
    ){
      /* 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
................................................................................
    assert( pPager->pInJournal==0 );

    if( pagerUseWal(pPager) ){
      /* If the pager is configured to use locking_mode=exclusive, and an
      ** exclusive lock on the database is not already held, obtain it now.
      */
      if( pPager->exclusiveMode && sqlite3WalExclusiveMode(pPager->pWal, -1) ){
        rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
        if( rc!=SQLITE_OK ){
          return rc;
        }
        sqlite3WalExclusiveMode(pPager->pWal, 1);
      }

      /* Grab the write lock on the log file. If successful, upgrade to
................................................................................
      rc = sqlite3WalBeginWriteTransaction(pPager->pWal);
    }else{
      /* Obtain a RESERVED lock on the database file. If the exFlag parameter
      ** is true, then immediately upgrade this to an EXCLUSIVE lock. The
      ** busy-handler callback can be used when upgrading to the EXCLUSIVE
      ** lock, but not when obtaining the RESERVED lock.
      */
      rc = pagerLockDb(pPager, RESERVED_LOCK);
      if( rc==SQLITE_OK && exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }


    if( rc==SQLITE_OK ){
................................................................................
** then savepoint iSavepoint is also destroyed.
**
** This function may return SQLITE_NOMEM if a memory allocation fails,
** or an IO error code if an IO error occurs while rolling back a 
** savepoint. If no errors occur, SQLITE_OK is returned.
*/ 
int sqlite3PagerSavepoint(Pager *pPager, int op, int iSavepoint){
  int rc = pPager->errCode;       /* Return code */

  assert( op==SAVEPOINT_RELEASE || op==SAVEPOINT_ROLLBACK );
  assert( iSavepoint>=0 || op==SAVEPOINT_ROLLBACK );

  if( rc==SQLITE_OK && iSavepoint<pPager->nSavepoint ){
    int ii;            /* Iterator variable */
    int nNew;          /* Number of remaining savepoints after this op. */

    /* Figure out how many savepoints will still be active after this
    ** operation. Store this value in nNew. Then free resources associated 
    ** with any savepoints that are destroyed by this operation.
    */
................................................................................
    ** the database file, so the playback operation can be skipped.
    */
    else if( pagerUseWal(pPager) || isOpen(pPager->jfd) ){
      PagerSavepoint *pSavepoint = (nNew==0)?0:&pPager->aSavepoint[nNew-1];
      rc = pagerPlaybackSavepoint(pPager, pSavepoint);
      assert(rc!=SQLITE_DONE);
    }
  }

  return rc;
}

/*
** Return the full pathname of the database file.
*/
const char *sqlite3PagerFilename(Pager *pPager){
................................................................................
      sqlite3PcacheDrop(pPgOld);
    }
  }

  origPgno = pPg->pgno;
  sqlite3PcacheMove(pPg, pgno);
  sqlite3PcacheMakeDirty(pPg);

  /* For an in-memory database, make sure the original page continues
  ** to exist, in case the transaction needs to roll back.  Use pPgOld
  ** as the original page since it has already been allocated.
  */
  if( MEMDB ){
    assert( pPgOld );
    sqlite3PcacheMove(pPgOld, origPgno);
    sqlite3PagerUnref(pPgOld);
  }

  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 
    ** "is journaled" bitvec flag has been set. This needs to be remedied by
    ** loading the page into the pager-cache and setting the PGHDR_NEED_SYNC
................................................................................
      return rc;
    }
    pPgHdr->flags |= PGHDR_NEED_SYNC;
    sqlite3PcacheMakeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }











  return SQLITE_OK;
}
#endif

/*
** Return a pointer to the data for the specified page.
*/
................................................................................
    assert( eOld==PAGER_JOURNALMODE_MEMORY || eOld==PAGER_JOURNALMODE_OFF );
    if( eMode!=PAGER_JOURNALMODE_MEMORY && eMode!=PAGER_JOURNALMODE_OFF ){
      eMode = eOld;
    }
  }

  if( eMode!=eOld ){









    /* Change the journal mode. */
    pPager->journalMode = (u8)eMode;

    /* When transistioning from TRUNCATE or PERSIST to any other journal
    ** mode except WAL (and we are not in locking_mode=EXCLUSIVE) then 
    ** delete the journal file.
................................................................................
    assert( (PAGER_JOURNALMODE_DELETE & 5)==0 );
    assert( (PAGER_JOURNALMODE_MEMORY & 5)==4 );
    assert( (PAGER_JOURNALMODE_OFF & 5)==0 );
    assert( (PAGER_JOURNALMODE_WAL & 5)==5 );

    assert( isOpen(pPager->fd) || pPager->exclusiveMode );
    if( !pPager->exclusiveMode && (eOld & 5)==1 && (eMode & 1)==0 ){

      sqlite3OsClose(pPager->jfd);

      /* In this case we would like to delete the journal file. If it is
      ** not possible, then that is not a problem. Deleting the journal file
      ** here is an optimization only.
      **
      ** Before deleting the journal file, obtain a RESERVED lock on the
      ** database file. This ensures that the journal file is not deleted
................................................................................
      int rc = SQLITE_OK;
      int state = pPager->eState;
      if( state==PAGER_NONE ){
        rc = sqlite3PagerSharedLock(pPager);
      }
      if( pPager->eState==PAGER_READER ){
        assert( rc==SQLITE_OK );
        rc = pagerLockDb(pPager, RESERVED_LOCK);
      }
      if( rc==SQLITE_OK ){
        sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
      }
      if( rc==SQLITE_OK && state==PAGER_READER ){
        pagerUnlockDb(pPager, SHARED_LOCK);
      }else if( state==PAGER_NONE ){
        pager_unlock(pPager);
      }
      assert( state==pPager->eState );
    }
  }

................................................................................

/*
** Return TRUE if the pager is in a state where it is OK to change the
** journalmode.  Journalmode changes can only happen when the database
** is unmodified.
*/
int sqlite3PagerOkToChangeJournalMode(Pager *pPager){
  assert( assert_pager_state(pPager) );
  if( pPager->eState>=PAGER_WRITER_CACHEMOD ) return 0;
  if( NEVER(isOpen(pPager->jfd) && pPager->journalOff>0) ) return 0;
  return 1;
}

/*
** Get/set the size-limit used for persistent journal files.
................................................................................
  assert( pPager->eState==PAGER_NONE   || pbOpen );
  assert( pPager->eState==PAGER_READER || !pbOpen );
  assert( pbOpen==0 || *pbOpen==0 );
  assert( pbOpen!=0 || (!pPager->tempFile && !pPager->pWal) );

  if( !pPager->tempFile && !pPager->pWal ){
    if( !sqlite3PagerWalSupported(pPager) ) return SQLITE_CANTOPEN;

    if( isOpen(pPager->jfd) ){
      sqlite3OsClose(pPager->jfd);
    }

    /* 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 ){
................................................................................

  /* If the log file is not already open, but does exist in the file-system,
  ** 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 = pagerLockDb(pPager, SHARED_LOCK);
    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,
................................................................................
    }
  }
    
  /* Checkpoint and close the log. Because an EXCLUSIVE lock is held on
  ** the database file, the log and log-summary files will be deleted.
  */
  if( rc==SQLITE_OK && pPager->pWal ){
    rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
    if( rc==SQLITE_OK ){
      rc = sqlite3WalClose(pPager->pWal,
                           (pPager->noSync ? 0 : pPager->sync_flags), 
        pPager->pageSize, (u8*)pPager->pTmpSpace
      );
      pPager->pWal = 0;
    }else{
      /* If we cannot get an EXCLUSIVE lock, downgrade the PENDING lock
      ** that we did get back to SHARED. */
      pagerUnlockDb(pPager, SQLITE_LOCK_SHARED);
    }
  }
  return rc;
}

#ifdef SQLITE_HAS_CODEC
/*