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Overview
Comment:Make wal_checkpoint a no-op if a prior checkpoint has already copied all WAL content into the database. This prevents a concurrent write to the database from resetting the wal-index out from under the WalIterator of the checkpoint as it is initializing.
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SHA1: cf86affcb7d3089496e9849cbf43a211097e4f64
User & Date: drh 2010-12-16 02:06:30
References
2011-02-20
03:20
Backport the changes of checkin [cf86affcb7d308949] ("Make wal_checkpoint a no-op if a prior checkpoint has already copied all WAL content into the database.") to the 3.7.4 release. check-in: e6e540ab user: drh tags: branch-3.7.4
Context
2010-12-16
19:52
Fix an assertion fault that can only occur if SQLITE_ENABLE_STAT2 is defined and the constant folding optimization is disabled using sqlite3_test_control(). Problem introduced by [ad8bc68197f2b4] but we missed it prior to the 3.7.4 release due to taking shortcuts and skipping tests in the release checklist. check-in: 70a3d817 user: drh tags: trunk
02:06
Make wal_checkpoint a no-op if a prior checkpoint has already copied all WAL content into the database. This prevents a concurrent write to the database from resetting the wal-index out from under the WalIterator of the checkpoint as it is initializing. check-in: cf86affc user: drh tags: trunk
2010-12-15
21:02
Enhanced comments in wal.c and declare some procedure parameters "const". No changes to the generated code. check-in: d0e4375b user: drh tags: trunk
Changes
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Changes to src/wal.c.

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  u32 mxPage;                     /* Max database page to write */
  int i;                          /* Loop counter */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  szPage = (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
  testcase( szPage<=32768 );
  testcase( szPage>=65536 );

  if( pWal->hdr.mxFrame==0 ) return SQLITE_OK;

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &pIter);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  assert( pIter );
................................................................................
  /* Compute in mxSafeFrame the index of the last frame of the WAL that is
  ** safe to write into the database.  Frames beyond mxSafeFrame might
  ** overwrite database pages that are in use by active readers and thus
  ** cannot be backfilled from the WAL.
  */
  mxSafeFrame = pWal->hdr.mxFrame;
  mxPage = pWal->hdr.nPage;
  pInfo = walCkptInfo(pWal);
  for(i=1; i<WAL_NREADER; i++){
    u32 y = pInfo->aReadMark[i];
    if( mxSafeFrame>=y ){
      assert( y<=pWal->hdr.mxFrame );
      rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
        pInfo->aReadMark[i] = READMARK_NOT_USED;







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  u32 mxPage;                     /* Max database page to write */
  int i;                          /* Loop counter */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  szPage = (pWal->hdr.szPage&0xfe00) + ((pWal->hdr.szPage&0x0001)<<16);
  testcase( szPage<=32768 );
  testcase( szPage>=65536 );
  pInfo = walCkptInfo(pWal);
  if( pInfo->nBackfill>=pWal->hdr.mxFrame ) return SQLITE_OK;

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &pIter);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  assert( pIter );
................................................................................
  /* Compute in mxSafeFrame the index of the last frame of the WAL that is
  ** safe to write into the database.  Frames beyond mxSafeFrame might
  ** overwrite database pages that are in use by active readers and thus
  ** cannot be backfilled from the WAL.
  */
  mxSafeFrame = pWal->hdr.mxFrame;
  mxPage = pWal->hdr.nPage;

  for(i=1; i<WAL_NREADER; i++){
    u32 y = pInfo->aReadMark[i];
    if( mxSafeFrame>=y ){
      assert( y<=pWal->hdr.mxFrame );
      rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
        pInfo->aReadMark[i] = READMARK_NOT_USED;