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SQLite training in Houston TX on 2019-11-05 (details)
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Overview
Comment:If a database file with the WAL flag set is opened in exclusive-locking mode, use heap memory to store the wal-index instead of shared-memory.
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SHA1: 8dd5c69198619866923c6053b71899c1fb8c4c67
User & Date: dan 2010-11-01 17:38:25
Context
2010-11-01
18:45
Add test cases to restore coverage of pager.c and wal.c. check-in: 6cae5529 user: dan tags: trunk
17:38
If a database file with the WAL flag set is opened in exclusive-locking mode, use heap memory to store the wal-index instead of shared-memory. check-in: 8dd5c691 user: dan tags: trunk
14:34
Change the version number to 3.7.4. check-in: db64843b user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/pager.c.

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** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is
** called, do not modify it. See the comment above the #define of 
** UNKNOWN_LOCK for an explanation of this.
*/
static int pagerUnlockDb(Pager *pPager, int eLock){
  int rc = SQLITE_OK;

  assert( !pPager->exclusiveMode );
  assert( eLock==NO_LOCK || eLock==SHARED_LOCK );
  assert( eLock!=NO_LOCK || pagerUseWal(pPager)==0 );
  if( isOpen(pPager->fd) ){
    assert( pPager->eLock>=eLock );
    rc = sqlite3OsUnlock(pPager->fd, eLock);
    if( pPager->eLock!=UNKNOWN_LOCK ){
      pPager->eLock = (u8)eLock;
................................................................................
*/
int sqlite3PagerLockingMode(Pager *pPager, int eMode){
  assert( eMode==PAGER_LOCKINGMODE_QUERY
            || eMode==PAGER_LOCKINGMODE_NORMAL
            || eMode==PAGER_LOCKINGMODE_EXCLUSIVE );
  assert( PAGER_LOCKINGMODE_QUERY<0 );
  assert( PAGER_LOCKINGMODE_NORMAL>=0 && PAGER_LOCKINGMODE_EXCLUSIVE>=0 );

  if( eMode>=0 && !pPager->tempFile ){
    pPager->exclusiveMode = (u8)eMode;
  }
  return (int)pPager->exclusiveMode;
}

/*
** Set the journal-mode for this pager. Parameter eMode must be one of:
................................................................................

/*
** Return true if the underlying VFS for the given pager supports the
** primitives necessary for write-ahead logging.
*/
int sqlite3PagerWalSupported(Pager *pPager){
  const sqlite3_io_methods *pMethods = pPager->fd->pMethods;
  return pMethods->iVersion>=2 && pMethods->xShmMap!=0;
}





















































/*
** The caller must be holding a SHARED lock on the database file to call
** this function.
**
** If the pager passed as the first argument is open on a real database
** file (not a temp file or an in-memory database), and the WAL file
................................................................................

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

    /* Close any rollback journal previously open */
    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 ){
      pPager->journalMode = PAGER_JOURNALMODE_WAL;
      pPager->eState = PAGER_OPEN;
    }
  }else{
    *pbOpen = 1;
  }
................................................................................
    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,
                          pPager->zWal, &pPager->pWal);
    }
  }
    
  /* 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
/*







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** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is
** called, do not modify it. See the comment above the #define of 
** UNKNOWN_LOCK for an explanation of this.
*/
static int pagerUnlockDb(Pager *pPager, int eLock){
  int rc = SQLITE_OK;

  assert( !pPager->exclusiveMode || pPager->eLock==eLock );
  assert( eLock==NO_LOCK || eLock==SHARED_LOCK );
  assert( eLock!=NO_LOCK || pagerUseWal(pPager)==0 );
  if( isOpen(pPager->fd) ){
    assert( pPager->eLock>=eLock );
    rc = sqlite3OsUnlock(pPager->fd, eLock);
    if( pPager->eLock!=UNKNOWN_LOCK ){
      pPager->eLock = (u8)eLock;
................................................................................
*/
int sqlite3PagerLockingMode(Pager *pPager, int eMode){
  assert( eMode==PAGER_LOCKINGMODE_QUERY
            || eMode==PAGER_LOCKINGMODE_NORMAL
            || eMode==PAGER_LOCKINGMODE_EXCLUSIVE );
  assert( PAGER_LOCKINGMODE_QUERY<0 );
  assert( PAGER_LOCKINGMODE_NORMAL>=0 && PAGER_LOCKINGMODE_EXCLUSIVE>=0 );
  assert( pPager->exclusiveMode || 0==sqlite3WalHeapMemory(pPager->pWal) );
  if( eMode>=0 && !pPager->tempFile && !sqlite3WalHeapMemory(pPager->pWal) ){
    pPager->exclusiveMode = (u8)eMode;
  }
  return (int)pPager->exclusiveMode;
}

/*
** Set the journal-mode for this pager. Parameter eMode must be one of:
................................................................................

/*
** Return true if the underlying VFS for the given pager supports the
** primitives necessary for write-ahead logging.
*/
int sqlite3PagerWalSupported(Pager *pPager){
  const sqlite3_io_methods *pMethods = pPager->fd->pMethods;
  return pPager->exclusiveMode || (pMethods->iVersion>=2 && pMethods->xShmMap);
}

/*
** Attempt to take an exclusive lock on the database file. If a PENDING lock
** is obtained instead, immediately release it.
*/
static int pagerExclusiveLock(Pager *pPager){
  int rc;                         /* Return code */

  assert( pPager->eLock==SHARED_LOCK || pPager->eLock==EXCLUSIVE_LOCK );
  rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
  if( rc!=SQLITE_OK ){
    /* If the attempt to grab the pending lock failed, release the 
    ** exclusive lock that may have been obtained instead.  */
    pagerUnlockDb(pPager, SHARED_LOCK);
  }

  return rc;
}

/*
** Call sqlite3WalOpen() to open the WAL handle. If the pager is in 
** exclusive-locking mode when this function is called, take an EXCLUSIVE
** lock on the database file and use heap-memory to store the wal-index
** in. Otherwise, use the normal shared-memory.
*/
static int pagerOpenWal(Pager *pPager){
  int rc = SQLITE_OK;

  assert( pPager->pWal==0 && pPager->tempFile==0 );
  assert( pPager->eLock==SHARED_LOCK || pPager->eLock==EXCLUSIVE_LOCK );

  /* If the pager is already in exclusive-mode, the WAL module will use 
  ** heap-memory for the wal-index instead of the VFS shared-memory 
  ** implementation. Take the exclusive lock now, before opening the WAL
  ** file, to make sure this is safe.
  */
  if( pPager->exclusiveMode ){
    rc = pagerExclusiveLock(pPager);
  }

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

  return rc;
}


/*
** The caller must be holding a SHARED lock on the database file to call
** this function.
**
** If the pager passed as the first argument is open on a real database
** file (not a temp file or an in-memory database), and the WAL file
................................................................................

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

    /* Close any rollback journal previously open */
    sqlite3OsClose(pPager->jfd);

    rc = pagerOpenWal(pPager);




    if( rc==SQLITE_OK ){
      pPager->journalMode = PAGER_JOURNALMODE_WAL;
      pPager->eState = PAGER_OPEN;
    }
  }else{
    *pbOpen = 1;
  }
................................................................................
    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 = pagerOpenWal(pPager);

    }
  }
    
  /* 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 = pagerExclusiveLock(pPager);
    if( rc==SQLITE_OK ){
      rc = sqlite3WalClose(pPager->pWal,
          (pPager->noSync ? 0 : pPager->sync_flags), 
          pPager->pageSize, (u8*)pPager->pTmpSpace
      );
      pPager->pWal = 0;




    }
  }
  return rc;
}

#ifdef SQLITE_HAS_CODEC
/*

Changes to src/test_vfs.c.

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**
** Available options are:
**
**   -noshm      BOOLEAN        (True to omit shm methods. Default false)
**   -default    BOOLEAN        (True to make the vfs default. Default false)
**   -szosfile   INTEGER        (Value for sqlite3_vfs.szOsFile)
**   -mxpathname INTEGER        (Value for sqlite3_vfs.mxPathname)

*/

#include "sqlite3.h"
#include "sqliteInt.h"

typedef struct Testvfs Testvfs;
typedef struct TestvfsShm TestvfsShm;







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**
** Available options are:
**
**   -noshm      BOOLEAN        (True to omit shm methods. Default false)
**   -default    BOOLEAN        (True to make the vfs default. Default false)
**   -szosfile   INTEGER        (Value for sqlite3_vfs.szOsFile)
**   -mxpathname INTEGER        (Value for sqlite3_vfs.mxPathname)
**   -iversion   INTEGER        (Value for sqlite3_vfs.iVersion)
*/

#include "sqlite3.h"
#include "sqliteInt.h"

typedef struct Testvfs Testvfs;
typedef struct TestvfsShm TestvfsShm;

Changes to src/wal.c.

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  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};








/*
** Each page of the wal-index mapping contains a hash-table made up of
** an array of HASHTABLE_NSLOT elements of the following type.
*/
typedef u16 ht_slot;

/*
................................................................................
           sizeof(u32*)*(iPage+1-pWal->nWiData));
    pWal->apWiData = apNew;
    pWal->nWiData = iPage+1;
  }

  /* Request a pointer to the required page from the VFS */
  if( pWal->apWiData[iPage]==0 ){




    rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, 
        pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
    );

  }

  *ppPage = pWal->apWiData[iPage];
  assert( iPage==0 || *ppPage || rc!=SQLITE_OK );
  return rc;
}

................................................................................
      aData += 2;
    }while( aData<aEnd );
  }

  aOut[0] = s1;
  aOut[1] = s2;
}







/*
** Write the header information in pWal->hdr into the wal-index.
**
** The checksum on pWal->hdr is updated before it is written.
*/
static void walIndexWriteHdr(Wal *pWal){
................................................................................
  const int nCksum = offsetof(WalIndexHdr, aCksum);

  assert( pWal->writeLock );
  pWal->hdr.isInit = 1;
  pWal->hdr.iVersion = WALINDEX_MAX_VERSION;
  walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum);
  memcpy((void *)&aHdr[1], (void *)&pWal->hdr, sizeof(WalIndexHdr));
  sqlite3OsShmBarrier(pWal->pDbFd);
  memcpy((void *)&aHdr[0], (void *)&pWal->hdr, sizeof(WalIndexHdr));
}

/*
** This function encodes a single frame header and writes it to a buffer
** supplied by the caller. A frame-header is made up of a series of 
** 4-byte big-endian integers, as follows:
................................................................................
  return rc;
}

/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){







  sqlite3OsShmUnmap(pWal->pDbFd, isDelete);

}

/* 
** Open a connection to the WAL file zWalName. The database file must 
** already be opened on connection pDbFd. The buffer that zWalName points
** to must remain valid for the lifetime of the returned Wal* handle.
**
................................................................................
** *ppWal is set to point to a new WAL handle. If an error occurs,
** an SQLite error code is returned and *ppWal is left unmodified.
*/
int sqlite3WalOpen(
  sqlite3_vfs *pVfs,              /* vfs module to open wal and wal-index */
  sqlite3_file *pDbFd,            /* The open database file */
  const char *zWalName,           /* Name of the WAL file */

  Wal **ppWal                     /* OUT: Allocated Wal handle */
){
  int rc;                         /* Return Code */
  Wal *pRet;                      /* Object to allocate and return */
  int flags;                      /* Flags passed to OsOpen() */

  assert( zWalName && zWalName[0] );
................................................................................
  }

  pRet->pVfs = pVfs;
  pRet->pWalFd = (sqlite3_file *)&pRet[1];
  pRet->pDbFd = pDbFd;
  pRet->readLock = -1;
  pRet->zWalName = zWalName;


  /* Open file handle on the write-ahead log file. */
  flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
  rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags);
  if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){
    pRet->readOnly = 1;
  }
................................................................................
    ** the database. In this case checkpoint the database and unlink both
    ** the wal and wal-index files.
    **
    ** The EXCLUSIVE lock is not released before returning.
    */
    rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){

      pWal->exclusiveMode = 1;

      rc = sqlite3WalCheckpoint(pWal, sync_flags, nBuf, zBuf);
      if( rc==SQLITE_OK ){
        isDelete = 1;
      }
    }

    walIndexClose(pWal, isDelete);
................................................................................
  ** There are two copies of the header at the beginning of the wal-index.
  ** When reading, read [0] first then [1].  Writes are in the reverse order.
  ** Memory barriers are used to prevent the compiler or the hardware from
  ** reordering the reads and writes.
  */
  aHdr = walIndexHdr(pWal);
  memcpy(&h1, (void *)&aHdr[0], sizeof(h1));
  sqlite3OsShmBarrier(pWal->pDbFd);
  memcpy(&h2, (void *)&aHdr[1], sizeof(h2));

  if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
    return 1;   /* Dirty read */
  }  
  if( h1.isInit==0 ){
    return 1;   /* Malformed header - probably all zeros */
................................................................................

  pInfo = walCkptInfo(pWal);
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){
    /* The WAL has been completely backfilled (or it is empty).
    ** and can be safely ignored.
    */
    rc = walLockShared(pWal, WAL_READ_LOCK(0));
    sqlite3OsShmBarrier(pWal->pDbFd);
    if( rc==SQLITE_OK ){
      if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
        /* It is not safe to allow the reader to continue here if frames
        ** may have been appended to the log before READ_LOCK(0) was obtained.
        ** When holding READ_LOCK(0), the reader ignores the entire log file,
        ** which implies that the database file contains a trustworthy
        ** snapshoT. Since holding READ_LOCK(0) prevents a checkpoint from
................................................................................
    **
    ** This does not guarantee that the copy of the wal-index header is up to
    ** date before proceeding. That would not be possible without somehow
    ** blocking writers. It only guarantees that a dangerous checkpoint or 
    ** log-wrap (either of which would require an exclusive lock on
    ** WAL_READ_LOCK(mxI)) has not occurred since the snapshot was valid.
    */
    sqlite3OsShmBarrier(pWal->pDbFd);
    if( pInfo->aReadMark[mxI]!=mxReadMark
     || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
    ){
      walUnlockShared(pWal, WAL_READ_LOCK(mxI));
      return WAL_RETRY;
    }else{
      assert( mxReadMark<=pWal->hdr.mxFrame );
................................................................................
** locking_mode=EXCLUSIVE.  This means that the pWal->readLock must
** be released.  Return 1 if the transition is made and 0 if the
** WAL is already in exclusive-locking mode - meaning that this
** routine is a no-op.  The pager must already hold the exclusive lock
** on the main database file before invoking this operation.
**
** If op is negative, then do a dry-run of the op==1 case but do
** not actually change anything.  The pager uses this to see if it
** should acquire the database exclusive lock prior to invoking
** the op==1 case.
*/
int sqlite3WalExclusiveMode(Wal *pWal, int op){
  int rc;
  assert( pWal->writeLock==0 );


  /* pWal->readLock is usually set, but might be -1 if there was a 
  ** prior error while attempting to acquire are read-lock. This cannot 
  ** happen if the connection is actually in exclusive mode (as no xShmLock
  ** locks are taken in this case). Nor should the pager attempt to
  ** upgrade to exclusive-mode following such an error.
  */
................................................................................
    pWal->exclusiveMode = 1;
    rc = 1;
  }else{
    rc = pWal->exclusiveMode==0;
  }
  return rc;
}










#endif /* #ifndef SQLITE_OMIT_WAL */







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  const char *zWalName;      /* Name of WAL file */
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};

/*
** Candidate values for Wal.exclusiveMode.
*/
#define WAL_NORMAL_MODE     0
#define WAL_EXCLUSIVE_MODE  1     
#define WAL_HEAPMEMORY_MODE 2

/*
** Each page of the wal-index mapping contains a hash-table made up of
** an array of HASHTABLE_NSLOT elements of the following type.
*/
typedef u16 ht_slot;

/*
................................................................................
           sizeof(u32*)*(iPage+1-pWal->nWiData));
    pWal->apWiData = apNew;
    pWal->nWiData = iPage+1;
  }

  /* Request a pointer to the required page from the VFS */
  if( pWal->apWiData[iPage]==0 ){
    if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){
      pWal->apWiData[iPage] = (u32 volatile *)sqlite3MallocZero(WALINDEX_PGSZ);
      if( !pWal->apWiData[iPage] ) rc = SQLITE_NOMEM;
    }else{
      rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, 
          pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
      );
    }
  }

  *ppPage = pWal->apWiData[iPage];
  assert( iPage==0 || *ppPage || rc!=SQLITE_OK );
  return rc;
}

................................................................................
      aData += 2;
    }while( aData<aEnd );
  }

  aOut[0] = s1;
  aOut[1] = s2;
}

static void walShmBarrier(Wal *pWal){
  if( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE ){
    sqlite3OsShmBarrier(pWal->pDbFd);
  }
}

/*
** Write the header information in pWal->hdr into the wal-index.
**
** The checksum on pWal->hdr is updated before it is written.
*/
static void walIndexWriteHdr(Wal *pWal){
................................................................................
  const int nCksum = offsetof(WalIndexHdr, aCksum);

  assert( pWal->writeLock );
  pWal->hdr.isInit = 1;
  pWal->hdr.iVersion = WALINDEX_MAX_VERSION;
  walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum);
  memcpy((void *)&aHdr[1], (void *)&pWal->hdr, sizeof(WalIndexHdr));
  walShmBarrier(pWal);
  memcpy((void *)&aHdr[0], (void *)&pWal->hdr, sizeof(WalIndexHdr));
}

/*
** This function encodes a single frame header and writes it to a buffer
** supplied by the caller. A frame-header is made up of a series of 
** 4-byte big-endian integers, as follows:
................................................................................
  return rc;
}

/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){
  if( pWal->exclusiveMode==WAL_HEAPMEMORY_MODE ){
    int i;
    for(i=0; i<pWal->nWiData; i++){
      sqlite3_free((void *)pWal->apWiData[i]);
      pWal->apWiData[i] = 0;
    }
  }else{
    sqlite3OsShmUnmap(pWal->pDbFd, isDelete);
  }
}

/* 
** Open a connection to the WAL file zWalName. The database file must 
** already be opened on connection pDbFd. The buffer that zWalName points
** to must remain valid for the lifetime of the returned Wal* handle.
**
................................................................................
** *ppWal is set to point to a new WAL handle. If an error occurs,
** an SQLite error code is returned and *ppWal is left unmodified.
*/
int sqlite3WalOpen(
  sqlite3_vfs *pVfs,              /* vfs module to open wal and wal-index */
  sqlite3_file *pDbFd,            /* The open database file */
  const char *zWalName,           /* Name of the WAL file */
  int bNoShm,                     /* True to run in heap-memory mode */
  Wal **ppWal                     /* OUT: Allocated Wal handle */
){
  int rc;                         /* Return Code */
  Wal *pRet;                      /* Object to allocate and return */
  int flags;                      /* Flags passed to OsOpen() */

  assert( zWalName && zWalName[0] );
................................................................................
  }

  pRet->pVfs = pVfs;
  pRet->pWalFd = (sqlite3_file *)&pRet[1];
  pRet->pDbFd = pDbFd;
  pRet->readLock = -1;
  pRet->zWalName = zWalName;
  pRet->exclusiveMode = (bNoShm ? WAL_HEAPMEMORY_MODE: WAL_NORMAL_MODE);

  /* Open file handle on the write-ahead log file. */
  flags = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
  rc = sqlite3OsOpen(pVfs, zWalName, pRet->pWalFd, flags, &flags);
  if( rc==SQLITE_OK && flags&SQLITE_OPEN_READONLY ){
    pRet->readOnly = 1;
  }
................................................................................
    ** the database. In this case checkpoint the database and unlink both
    ** the wal and wal-index files.
    **
    ** The EXCLUSIVE lock is not released before returning.
    */
    rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      if( pWal->exclusiveMode==WAL_NORMAL_MODE ){
        pWal->exclusiveMode = WAL_EXCLUSIVE_MODE;
      }
      rc = sqlite3WalCheckpoint(pWal, sync_flags, nBuf, zBuf);
      if( rc==SQLITE_OK ){
        isDelete = 1;
      }
    }

    walIndexClose(pWal, isDelete);
................................................................................
  ** There are two copies of the header at the beginning of the wal-index.
  ** When reading, read [0] first then [1].  Writes are in the reverse order.
  ** Memory barriers are used to prevent the compiler or the hardware from
  ** reordering the reads and writes.
  */
  aHdr = walIndexHdr(pWal);
  memcpy(&h1, (void *)&aHdr[0], sizeof(h1));
  walShmBarrier(pWal);
  memcpy(&h2, (void *)&aHdr[1], sizeof(h2));

  if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
    return 1;   /* Dirty read */
  }  
  if( h1.isInit==0 ){
    return 1;   /* Malformed header - probably all zeros */
................................................................................

  pInfo = walCkptInfo(pWal);
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){
    /* The WAL has been completely backfilled (or it is empty).
    ** and can be safely ignored.
    */
    rc = walLockShared(pWal, WAL_READ_LOCK(0));
    walShmBarrier(pWal);
    if( rc==SQLITE_OK ){
      if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
        /* It is not safe to allow the reader to continue here if frames
        ** may have been appended to the log before READ_LOCK(0) was obtained.
        ** When holding READ_LOCK(0), the reader ignores the entire log file,
        ** which implies that the database file contains a trustworthy
        ** snapshoT. Since holding READ_LOCK(0) prevents a checkpoint from
................................................................................
    **
    ** This does not guarantee that the copy of the wal-index header is up to
    ** date before proceeding. That would not be possible without somehow
    ** blocking writers. It only guarantees that a dangerous checkpoint or 
    ** log-wrap (either of which would require an exclusive lock on
    ** WAL_READ_LOCK(mxI)) has not occurred since the snapshot was valid.
    */
    walShmBarrier(pWal);
    if( pInfo->aReadMark[mxI]!=mxReadMark
     || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
    ){
      walUnlockShared(pWal, WAL_READ_LOCK(mxI));
      return WAL_RETRY;
    }else{
      assert( mxReadMark<=pWal->hdr.mxFrame );
................................................................................
** locking_mode=EXCLUSIVE.  This means that the pWal->readLock must
** be released.  Return 1 if the transition is made and 0 if the
** WAL is already in exclusive-locking mode - meaning that this
** routine is a no-op.  The pager must already hold the exclusive lock
** on the main database file before invoking this operation.
**
** If op is negative, then do a dry-run of the op==1 case but do
** not actually change anything. The pager uses this to see if it
** should acquire the database exclusive lock prior to invoking
** the op==1 case.
*/
int sqlite3WalExclusiveMode(Wal *pWal, int op){
  int rc;
  assert( pWal->writeLock==0 );
  assert( pWal->exclusiveMode!=WAL_HEAPMEMORY_MODE || op==-1 );

  /* pWal->readLock is usually set, but might be -1 if there was a 
  ** prior error while attempting to acquire are read-lock. This cannot 
  ** happen if the connection is actually in exclusive mode (as no xShmLock
  ** locks are taken in this case). Nor should the pager attempt to
  ** upgrade to exclusive-mode following such an error.
  */
................................................................................
    pWal->exclusiveMode = 1;
    rc = 1;
  }else{
    rc = pWal->exclusiveMode==0;
  }
  return rc;
}

/* 
** Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal){
  return (pWal && pWal->exclusiveMode==WAL_HEAPMEMORY_MODE );
}

#endif /* #ifndef SQLITE_OMIT_WAL */

Changes to src/wal.h.

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# define sqlite3WalUndo(x,y,z)                 0
# define sqlite3WalSavepoint(y,z)
# define sqlite3WalSavepointUndo(y,z)          0
# define sqlite3WalFrames(u,v,w,x,y,z)         0
# define sqlite3WalCheckpoint(u,v,w,x)         0
# define sqlite3WalCallback(z)                 0
# define sqlite3WalExclusiveMode(y,z)          0

#else

#define WAL_SAVEPOINT_NDATA 4

/* Connection to a write-ahead log (WAL) file. 
** There is one object of this type for each pager. 
*/
typedef struct Wal Wal;

/* Open and close a connection to a write-ahead log. */
int sqlite3WalOpen(sqlite3_vfs*, sqlite3_file*, const char *zName, Wal**);
int sqlite3WalClose(Wal *pWal, int sync_flags, int, u8 *);

/* Used by readers to open (lock) and close (unlock) a snapshot.  A 
** snapshot is like a read-transaction.  It is the state of the database
** at an instant in time.  sqlite3WalOpenSnapshot gets a read lock and
** preserves the current state even if the other threads or processes
** write to or checkpoint the WAL.  sqlite3WalCloseSnapshot() closes the
................................................................................
*/
int sqlite3WalCallback(Wal *pWal);

/* Tell the wal layer that an EXCLUSIVE lock has been obtained (or released)
** by the pager layer on the database file.
*/
int sqlite3WalExclusiveMode(Wal *pWal, int op);







#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */







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# define sqlite3WalUndo(x,y,z)                 0
# define sqlite3WalSavepoint(y,z)
# define sqlite3WalSavepointUndo(y,z)          0
# define sqlite3WalFrames(u,v,w,x,y,z)         0
# define sqlite3WalCheckpoint(u,v,w,x)         0
# define sqlite3WalCallback(z)                 0
# define sqlite3WalExclusiveMode(y,z)          0
# define sqlite3WalHeapMemory(z)               0
#else

#define WAL_SAVEPOINT_NDATA 4

/* Connection to a write-ahead log (WAL) file. 
** There is one object of this type for each pager. 
*/
typedef struct Wal Wal;

/* Open and close a connection to a write-ahead log. */
int sqlite3WalOpen(sqlite3_vfs*, sqlite3_file*, const char *zName, int, Wal**);
int sqlite3WalClose(Wal *pWal, int sync_flags, int, u8 *);

/* Used by readers to open (lock) and close (unlock) a snapshot.  A 
** snapshot is like a read-transaction.  It is the state of the database
** at an instant in time.  sqlite3WalOpenSnapshot gets a read lock and
** preserves the current state even if the other threads or processes
** write to or checkpoint the WAL.  sqlite3WalCloseSnapshot() closes the
................................................................................
*/
int sqlite3WalCallback(Wal *pWal);

/* Tell the wal layer that an EXCLUSIVE lock has been obtained (or released)
** by the pager layer on the database file.
*/
int sqlite3WalExclusiveMode(Wal *pWal, int op);

/* Return true if the argument is non-NULL and the WAL module is using
** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
** WAL module is using shared-memory, return false. 
*/
int sqlite3WalHeapMemory(Wal *pWal);

#endif /* ifndef SQLITE_OMIT_WAL */
#endif /* _WAL_H_ */

Changes to test/pager1.test.

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    3  {
      BEGIN;
        SELECT * FROM t1;
      COMMIT;
    } {1 2} 0 -1
  
    4  { PRAGMA journal_mode = WAL }    wal    -1 -1
    5  { INSERT INTO t1 VALUES(3, 4) }  {}     -1 [wal_file_size 1 1024]
    6  { PRAGMA locking_mode = NORMAL } normal -1 [wal_file_size 1 1024]
    7  { INSERT INTO t1 VALUES(5, 6); } {}     -1 [wal_file_size 2 1024]
  
    8  { PRAGMA journal_mode = TRUNCATE } truncate          0 -1
    9  { INSERT INTO t1 VALUES(7, 8) }    {}                0 -1
    10 { SELECT * FROM t1 }               {1 2 3 4 5 6 7 8} 0 -1
  
  }] {
    do_execsql_test pager1-7.1.$tn.1 $sql $res







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    3  {
      BEGIN;
        SELECT * FROM t1;
      COMMIT;
    } {1 2} 0 -1
  
    4  { PRAGMA journal_mode = WAL }    wal       -1 -1
    5  { INSERT INTO t1 VALUES(3, 4) }  {}        -1 [wal_file_size 1 1024]
    6  { PRAGMA locking_mode = NORMAL } exclusive -1 [wal_file_size 1 1024]
    7  { INSERT INTO t1 VALUES(5, 6); } {}        -1 [wal_file_size 2 1024]
  
    8  { PRAGMA journal_mode = TRUNCATE } truncate          0 -1
    9  { INSERT INTO t1 VALUES(7, 8) }    {}                0 -1
    10 { SELECT * FROM t1 }               {1 2 3 4 5 6 7 8} 0 -1
  
  }] {
    do_execsql_test pager1-7.1.$tn.1 $sql $res

Changes to test/permutations.test.

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#   coverage-wal
#
test_suite "coverage-wal" -description {
  Coverage tests for file wal.c.
} -files {
  wal.test       wal2.test     wal3.test       walmode.test    
  walbak.test    walhook.test  walcrash2.test  walcksum.test
  walfault.test  walbig.test
} 

test_suite "coverage-pager" -description {
  Coverage tests for file pager.c.
} -files {
  pager1.test    pager2.test  pagerfault.test  pagerfault2.test
  walfault.test  walbak.test  journal2.test    tkt-9d68c883.test







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#   coverage-wal
#
test_suite "coverage-wal" -description {
  Coverage tests for file wal.c.
} -files {
  wal.test       wal2.test     wal3.test       walmode.test    
  walbak.test    walhook.test  walcrash2.test  walcksum.test
  walfault.test  walbig.test   walnoshm.test
} 

test_suite "coverage-pager" -description {
  Coverage tests for file pager.c.
} -files {
  pager1.test    pager2.test  pagerfault.test  pagerfault2.test
  walfault.test  walbak.test  journal2.test    tkt-9d68c883.test

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# Invoke the do_test procedure to run a single test 
#
proc do_test {name cmd expected} {

  global argv cmdlinearg



  sqlite3_memdebug_settitle $name

#  if {[llength $argv]==0} { 
#    set go 1
#  } else {
#    set go 0







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# Invoke the do_test procedure to run a single test 
#
proc do_test {name cmd expected} {

  global argv cmdlinearg

  fix_testname name

  sqlite3_memdebug_settitle $name

#  if {[llength $argv]==0} { 
#    set go 1
#  } else {
#    set go 0

Changes to test/wal2.test.

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#               connection silently remains in exclusive mode.
#
do_test wal2-6.1.1 {
  file delete -force test.db test.db-wal test.db-journal
  sqlite3 db test.db
  execsql {
    Pragma Journal_Mode = Wal;
    Pragma Locking_Mode = Exclusive;
  }
} {wal exclusive}
do_test wal2-6.1.2 {
  execsql { PRAGMA lock_status }
} {main unlocked temp closed}
do_test wal2-6.1.3 {




  execsql {
    BEGIN;
      CREATE TABLE t1(a, b);
      INSERT INTO t1 VALUES(1, 2);
    COMMIT;
    PRAGMA lock_status;
  }
................................................................................
    COMMIT;
    Pragma loCK_STATus;
  }
} {main exclusive temp closed}
do_test wal2-6.2.3 {
  db close
  sqlite3 db test.db

  execsql { PRAGMA LOCKING_MODE = EXCLUSIVE }
} {exclusive}
do_test wal2-6.2.4 {
  execsql {
    SELECT * FROM t1;
    pragma lock_status;
  }
................................................................................
  return SQLITE_OK
}
do_test wal2-6.6.1 {
  testvfs T
  T script lock_control
  T filter {}
  sqlite3 db test.db -vfs T

  execsql { PRAGMA locking_mode = exclusive }
  execsql { INSERT INTO t2 VALUES('V', 'VI') }
} {}
do_test wal2-6.6.2 {
  execsql { PRAGMA locking_mode = normal }
  T filter xShmLock
  execsql { INSERT INTO t2 VALUES('VII', 'VIII') }
................................................................................
  catchsql { SELECT * FROM t2 } db2
} {1 {database is locked}}
do_test wal2-6.6.2 {
  db2 close
  T filter {}
  execsql { INSERT INTO t2 VALUES('IX', 'X') }
} {}
do_test wal2-6.6.3 {
  # This time, we have successfully exited exclusive mode. So the second
  # connection can read the database.
  sqlite3 db2 test.db -vfs T
  catchsql { SELECT * FROM t2 } db2
} {0 {I II III IV V VI VII VIII IX X}}

db close







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#               connection silently remains in exclusive mode.
#
do_test wal2-6.1.1 {
  file delete -force test.db test.db-wal test.db-journal
  sqlite3 db test.db
  execsql {
    Pragma Journal_Mode = Wal;

  }
} {wal}
do_test wal2-6.1.2 {
  execsql { PRAGMA lock_status }
} {main unlocked temp closed}
do_test wal2-6.1.3 {
  execsql {
    SELECT * FROM sqlite_master;
    Pragma Locking_Mode = Exclusive;
  }
  execsql {
    BEGIN;
      CREATE TABLE t1(a, b);
      INSERT INTO t1 VALUES(1, 2);
    COMMIT;
    PRAGMA lock_status;
  }
................................................................................
    COMMIT;
    Pragma loCK_STATus;
  }
} {main exclusive temp closed}
do_test wal2-6.2.3 {
  db close
  sqlite3 db test.db
  execsql { SELECT * FROM sqlite_master }
  execsql { PRAGMA LOCKING_MODE = EXCLUSIVE }
} {exclusive}
do_test wal2-6.2.4 {
  execsql {
    SELECT * FROM t1;
    pragma lock_status;
  }
................................................................................
  return SQLITE_OK
}
do_test wal2-6.6.1 {
  testvfs T
  T script lock_control
  T filter {}
  sqlite3 db test.db -vfs T
  execsql { SELECT * FROM sqlite_master }
  execsql { PRAGMA locking_mode = exclusive }
  execsql { INSERT INTO t2 VALUES('V', 'VI') }
} {}
do_test wal2-6.6.2 {
  execsql { PRAGMA locking_mode = normal }
  T filter xShmLock
  execsql { INSERT INTO t2 VALUES('VII', 'VIII') }
................................................................................
  catchsql { SELECT * FROM t2 } db2
} {1 {database is locked}}
do_test wal2-6.6.2 {
  db2 close
  T filter {}
  execsql { INSERT INTO t2 VALUES('IX', 'X') }
} {}
do_test wal2-6.6.4 {
  # This time, we have successfully exited exclusive mode. So the second
  # connection can read the database.
  sqlite3 db2 test.db -vfs T
  catchsql { SELECT * FROM t2 } db2
} {0 {I II III IV V VI VII VIII IX X}}

db close

Changes to test/walfault.test.

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  set rc [sqlite3_wal_checkpoint db]
  if {$rc != "SQLITE_OK"} { error [sqlite3_errmsg db] }
} -test {
  db close
  faultsim_test_result {0 {}}
}






































































finish_test







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  set rc [sqlite3_wal_checkpoint db]
  if {$rc != "SQLITE_OK"} { error [sqlite3_errmsg db] }
} -test {
  db close
  faultsim_test_result {0 {}}
}

#-------------------------------------------------------------------------
# Test simple recovery, reading and writing a database file using a 
# heap-memory wal-index.
# 
do_test walfault-13-pre-1 {
  faultsim_delete_and_reopen
  execsql {
    PRAGMA journal_mode = WAL;
    PRAGMA wal_autocheckpoint = 0;
    BEGIN;
      CREATE TABLE abc(a PRIMARY KEY);
      INSERT INTO abc VALUES(randomblob(1500));
      INSERT INTO abc VALUES(randomblob(1500));
    COMMIT;
  }
  faultsim_save_and_close
  file delete sv_test.db-shm
} {}

do_faultsim_test walfault-13.1 -prep {
  faultsim_restore_and_reopen
} -body {
  db eval { PRAGMA locking_mode = exclusive }
  db eval { SELECT count(*) FROM abc }
} -test {
  faultsim_test_result {0 2}
  if {[file exists test.db-shm]} { error "Not using heap-memory mode" }
  faultsim_integrity_check
}

do_faultsim_test walfault-13.2 -prep {
  faultsim_restore_and_reopen
  db eval { PRAGMA locking_mode = exclusive }
} -body {
  db eval { PRAGMA journal_mode = delete }
} -test {
  faultsim_test_result {0 delete}
  if {[file exists test.db-shm]} { error "Not using heap-memory mode" }
  faultsim_integrity_check
}

do_test walfault-13-pre-2 {
  faultsim_delete_and_reopen
  execsql {
    BEGIN;
      CREATE TABLE abc(a PRIMARY KEY);
      INSERT INTO abc VALUES(randomblob(1500));
      INSERT INTO abc VALUES(randomblob(1500));
    COMMIT;
  }
  faultsim_save_and_close
} {}

do_faultsim_test walfault-13.3 -prep {
  faultsim_restore_and_reopen
} -body {
  db eval { 
    PRAGMA locking_mode = exclusive;
    PRAGMA journal_mode = WAL;
    INSERT INTO abc VALUES(randomblob(1500));
  }
} -test {
  faultsim_test_result {0 {exclusive wal}}
  if {[file exists test.db-shm]} { error "Not using heap-memory mode" }
  faultsim_integrity_check
  set nRow [db eval {SELECT count(*) FROM abc}]
  if {!(($nRow==2 && $testrc) || $nRow==3)} { error "Bad db content" }
}

finish_test

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# 2010 November 1
#
# 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 file is testing that WAL databases may be accessed without
# using the xShm primitives if the connection is in exclusive-mode.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix walnoshm
ifcapable !wal {finish_test ; return }

db close
testvfs tvfsshm
testvfs tvfs -default 1 -iversion 1 
sqlite3 db test.db

#--------------------------------------------------------------------------
# Test that when using a version 1 VFS, a database can only be converted
# to WAL mode after setting locking_mode=EXCLUSIVE. Also, test that if a
# WAL database is opened using heap-memory for the WAL index, the connection
# cannot change back to locking_mode=NORMAL while the database is still in
# WAL mode.
#
do_execsql_test 1.1 {
  CREATE TABLE t1(x, y);
  INSERT INTO t1 VALUES(1, 2);
}

do_execsql_test 1.2 { 
  PRAGMA journal_mode = WAL;
  SELECT * FROM t1;
} {delete 1 2}
do_test 1.3 { file exists test.db-wal } {0}

do_execsql_test 1.4 { 
  PRAGMA locking_mode = exclusive;
  PRAGMA journal_mode = WAL;
  SELECT * FROM t1;
} {exclusive wal 1 2}
do_test 1.5 { file exists test.db-wal } {1}

do_execsql_test 1.6 { INSERT INTO t1 VALUES(3, 4) }

do_execsql_test 1.7 {
  PRAGMA locking_mode = normal;
} {exclusive}
do_execsql_test 1.8 {
  PRAGMA journal_mode = delete;
  PRAGMA main.locking_mode;
} {delete exclusive}
do_execsql_test 1.9 {
  PRAGMA locking_mode = normal;
} {normal}
do_execsql_test 1.10 {
  SELECT * FROM t1;
} {1 2 3 4}
do_test 1.11 { file exists test.db-wal } {0}

#-------------------------------------------------------------------------
#
# 2.1.*: Test that a connection using a version 1 VFS can open a WAL database
#        and convert it to rollback mode if it is set to use
#        locking_mode=exclusive.
#
# 2.2.*: Test that if the exclusive lock cannot be obtained while attempting
#        the above, the operation fails and the WAL file is not opened.
#
do_execsql_test 2.1.1 {
  CREATE TABLE t2(x, y);
  INSERT INTO t2 VALUES('a', 'b');
  INSERT INTO t2 VALUES('c', 'd');
}
do_execsql_test 2.1.2 {
  PRAGMA locking_mode = exclusive;
  PRAGMA journal_mode = WAL;
  INSERT INTO t2 VALUES('e', 'f');
  INSERT INTO t2 VALUES('g', 'h');
} {exclusive wal}

do_test 2.1.3 {
  file copy -force test.db     test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3 db2 test2.db
  catchsql { SELECT * FROM t2 } db2
} {1 {unable to open database file}}
do_test 2.1.4 {
  catchsql { PRAGMA journal_mode = delete } db2
} {1 {unable to open database file}}
do_test 2.1.5 {
  execsql { 
    PRAGMA locking_mode = exclusive; 
    PRAGMA journal_mode = delete;
    SELECT * FROM t2;
  } db2
} {exclusive delete a b c d e f g h}

do_test 2.2.1 {
  file copy -force test.db     test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3 db3 test2.db -vfs tvfsshm
  sqlite3 db2 test2.db
  execsql { SELECT * FROM t2 } db3
} {a b c d e f g h}

do_test 2.2.2 {
  execsql  { PRAGMA locking_mode = exclusive }  db2
  catchsql { PRAGMA journal_mode = delete } db2
} {1 {database is locked}}

do_test 2.2.3 {
  # This is to test that [db2] is not holding a PENDING lock (which can 
  # happen when an attempt to obtain an EXCLUSIVE lock fails).
  sqlite3 db4 test2.db -vfs tvfsshm
  execsql { SELECT * FROM t2 } db4
} {a b c d e f g h}

do_test 2.2.4 {
  catchsql { SELECT * FROM t2 } db2
} {1 {database is locked}}

do_test 2.2.5 {
  db4 close
  sqlite3 db4 test2.db -vfs tvfsshm
  execsql { SELECT * FROM t2 } db4
} {a b c d e f g h}

do_test 2.2.6 {
  db3 close
  db4 close
  execsql { SELECT * FROM t2 } db2
} {a b c d e f g h}

db2 close


finish_test