SQLite: Check-in [8c9ee1d7]

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Overview

Comment:	Amplification of a comment in wal.c. Change the aReadMark[] processing so that one read mark is left at zero when a WAL resets.
Downloads:	Tarball \| ZIP archive \| SQL archive
Timelines:	family \| ancestors \| descendants \| both \| trunk
Files:	files \| file ages \| folders
SHA1:	8c9ee1d78f99394eef73a177141ca9e1c67e4e07
User & Date:	drh 2012-07-17 02:56:05

References

2012-07-17
17:46		Cherrypick [8c9ee1d78f] and [e416359633] from trunk: Ensure that there is always at least one aReadMark slot usable by an unprivileged reader while a checkpoint is running. Also, if one or more transactions are recovered from a log file, initialize one of the aReadMark slots to contain mxFrame as part of the recovery process. (check-in: 65035912 user: drh tags: apple-osx)

Context

2012-07-17
14:37		Ensure that there is always at least one aReadMark slot usable by an unprivileged reader while a checkpoint is running. Also, if one or more transactions are recovered from a log file, initialize one of the aReadMark slots to contain mxFrame as part of the recovery process. (check-in: e4163596 user: dan tags: trunk)
02:56		Amplification of a comment in wal.c. Change the aReadMark[] processing so that one read mark is left at zero when a WAL resets. (check-in: 8c9ee1d7 user: drh tags: trunk)
2012-07-16
23:13		Merge the spellfix1 changes for supporting matchlen into trunk. (check-in: 6f167adf user: drh tags: trunk)

Changes

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Changes to src/wal.c.

** connection to it closes.  Because the wal-index is transient, it can
** use an architecture-specific format; it does not have to be cross-platform.
** Hence, unlike the database and WAL file formats which store all values
** as big endian, the wal-index can store multi-byte values in the native
** byte order of the host computer.
**
** The purpose of the wal-index is to answer this question quickly:  Given
** a page number P, return the index of the last frame for page P in the WAL,

** or return NULL if there are no frames for page P in the WAL.
**
** The wal-index consists of a header region, followed by an one or
** more index blocks.  
**
** The wal-index header contains the total number of frames within the WAL
** in the the mxFrame field.  
**
................................................................................

        pWal->nCkpt++;
        pWal->hdr.mxFrame = 0;
        sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
        aSalt[1] = salt1;
        walIndexWriteHdr(pWal);
        pInfo->nBackfill = 0;

        for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
        assert( pInfo->aReadMark[0]==0 );
        walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      }else if( rc!=SQLITE_BUSY ){
        return rc;
      }
    }
    walUnlockShared(pWal, WAL_READ_LOCK(0));

** connection to it closes.  Because the wal-index is transient, it can
** use an architecture-specific format; it does not have to be cross-platform.
** Hence, unlike the database and WAL file formats which store all values
** as big endian, the wal-index can store multi-byte values in the native
** byte order of the host computer.
**
** The purpose of the wal-index is to answer this question quickly:  Given
** a page number P and a maximum frame index M, return the index of the 
** last frame in the wal before frame M for page P in the WAL, or return
** NULL if there are no frames for page P in the WAL prior to M.
**
** The wal-index consists of a header region, followed by an one or
** more index blocks.  
**
** The wal-index header contains the total number of frames within the WAL
** in the the mxFrame field.  
**
................................................................................

        pWal->nCkpt++;
        pWal->hdr.mxFrame = 0;
        sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
        aSalt[1] = salt1;
        walIndexWriteHdr(pWal);
        pInfo->nBackfill = 0;
        pInfo->aReadMark[1] = 0;
        for(i=2; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
        assert( pInfo->aReadMark[0]==0 );
        walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      }else if( rc!=SQLITE_BUSY ){
        return rc;
      }
    }
    walUnlockShared(pWal, WAL_READ_LOCK(0));