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Overview
Comment:Fix a bug whereby an old snapshot could be checkpointed (and subsequent transactions discarded) if the last connection to disconnect from a WAL database happended to be holding an out-of-date wal-index header.
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SHA1: d0c0034b0baa83046c1d6b94c886f7039e4e06f5
User & Date: dan 2010-05-06 17:28:09
Context
2010-05-06
18:04
Only pass -1 as the size parameter to xShmGet when the caller does not care what size mapping is returned. Only call xShmSize when the underlying allocation (not the mapping) should be resized. check-in: 637f51dd user: dan tags: trunk
17:28
Fix a bug whereby an old snapshot could be checkpointed (and subsequent transactions discarded) if the last connection to disconnect from a WAL database happended to be holding an out-of-date wal-index header. check-in: d0c0034b user: dan tags: trunk
16:06
After throwing an error to say that one cannot change into WAL mode within a tranactions, do not then go and change into WAL mode. check-in: 56a17dae user: drh tags: trunk
Changes
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Changes to src/wal.c.

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static int walIndexEntry(u32 iFrame){
  return (
      (WALINDEX_LOCK_OFFSET+WALINDEX_LOCK_RESERVED)/sizeof(u32)
    + (((iFrame-1)>>8)<<6)        /* Indexes that occur before iFrame */
    + iFrame-1                    /* Db page numbers that occur before iFrame */
  );
}














/*
** Release our reference to the wal-index memory map, if we are holding
** it.
*/
static void walIndexUnmap(Wal *pWal){
  if( pWal->pWiData ){
................................................................................
    ** 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(pFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      rc = walCheckpoint(pWal, pFd, sync_flags, nBuf, zBuf);
      if( rc==SQLITE_OK ){
        isDelete = 1;
      }
      walIndexUnmap(pWal);
    }

    walIndexClose(pWal, isDelete);







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static int walIndexEntry(u32 iFrame){
  return (
      (WALINDEX_LOCK_OFFSET+WALINDEX_LOCK_RESERVED)/sizeof(u32)
    + (((iFrame-1)>>8)<<6)        /* Indexes that occur before iFrame */
    + iFrame-1                    /* Db page numbers that occur before iFrame */
  );
}

/*
** Return the minimum mapping size in bytes that can be used to read the
** wal-index up to and including frame iFrame. If iFrame is the last frame
** in a block of 256 frames, the returned byte-count includes the space
** required by the 256-byte index block.
*/
static int walMappingSize(u32 iFrame){
  return ( WALINDEX_LOCK_OFFSET + WALINDEX_LOCK_RESERVED 
         + iFrame*sizeof(u32)
         + (iFrame>>8)*256
  );
}

/*
** Release our reference to the wal-index memory map, if we are holding
** it.
*/
static void walIndexUnmap(Wal *pWal){
  if( pWal->pWiData ){
................................................................................
    ** 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(pFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      rc = sqlite3WalCheckpoint(pWal, pFd, sync_flags, nBuf, zBuf, 0, 0);
      if( rc==SQLITE_OK ){
        isDelete = 1;
      }
      walIndexUnmap(pWal);
    }

    walIndexClose(pWal, isDelete);

Changes to test/wal.test.

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  execsql { SELECT count(*) FROM t2 ; SELECT count(*) FROM t1 } db2
} {1 2}
do_test wal-4.5.7 {
  execsql { PRAGMA integrity_check } db2
} {ok}
db2 close
















reopen_db
do_test wal-5.1 {
  execsql {
    CREATE TEMP TABLE t2(a, b);
    INSERT INTO t2 VALUES(1, 2);
  }
................................................................................
      set rc [catch { db one {PRAGMA integrity_check} } msg]
      expr { $rc!=0 || $msg!="ok" }
    } $works
  
    db close
  }
}













































catch { db2 close }
catch { db close }

finish_test








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  execsql { SELECT count(*) FROM t2 ; SELECT count(*) FROM t1 } db2
} {1 2}
do_test wal-4.5.7 {
  execsql { PRAGMA integrity_check } db2
} {ok}
db2 close

do_test wal-4.6.1 {
  execsql {
    DELETE FROM t2;
    PRAGMA wal_checkpoint;
    BEGIN;
      INSERT INTO t2 VALUES('w', 'x');
      SAVEPOINT save;
        INSERT INTO t2 VALUES('y', 'z');
      ROLLBACK TO save;
    COMMIT;
    SELECT * FROM t2;
  }
} {w x}


reopen_db
do_test wal-5.1 {
  execsql {
    CREATE TEMP TABLE t2(a, b);
    INSERT INTO t2 VALUES(1, 2);
  }
................................................................................
      set rc [catch { db one {PRAGMA integrity_check} } msg]
      expr { $rc!=0 || $msg!="ok" }
    } $works
  
    db close
  }
}

#-------------------------------------------------------------------------
# The following test - wal-19.* - fixes a bug that was present during
# development.
#
# When a database connection in WAL mode is closed, it attempts an
# EXCLUSIVE lock on the database file. If the lock is obtained, the
# connection knows that it is the last connection to disconnect from
# the database, so it runs a checkpoint operation. The bug was that
# the connection was not updating its private copy of the wal-index 
# header before doing so, meaning that it could checkpoint an old
# snapshot.
#
do_test wal-19.1 {
  file delete -force test.db test.db-wal test.db-journal
  sqlite3 db test.db
  sqlite3 db2 test.db
  execsql {
    PRAGMA journal_mode = WAL;
    CREATE TABLE t1(a, b);
    INSERT INTO t1 VALUES(1, 2);
    INSERT INTO t1 VALUES(3, 4);
  }
  execsql { SELECT * FROM t1 } db2
} {1 2 3 4}
do_test wal-19.2 {
  execsql {
    INSERT INTO t1 VALUES(5, 6);
    SELECT * FROM t1;
  }
} {1 2 3 4 5 6}
do_test wal-19.3 {
  db close
  db2 close
  file exists test.db-wal
} {0}
do_test wal-19.4 {
  # When the bug was present, the following was returning {1 2 3 4} only,
  # as [db2] had an out-of-date copy of the wal-index header when it was
  # closed.
  #
  sqlite3 db test.db
  execsql { SELECT * FROM t1 }
} {1 2 3 4 5 6}

catch { db2 close }
catch { db close }

finish_test