diff options
Diffstat (limited to 'src/wal.c')
| -rw-r--r-- | src/wal.c | 97 |
1 files changed, 74 insertions, 23 deletions
@@ -1524,6 +1524,26 @@ static int walIteratorInit(Wal *pWal, WalIterator **pp){ } /* +** Attempt to obtain the exclusive WAL lock defined by parameters lockIdx and +** n. If the attempt fails and parameter xBusy is not NULL, then it is a +** busy-handler function. Invoke it and retry the lock until either the +** lock is successfully obtained or the busy-handler returns 0. +*/ +static int walBusyLock( + Wal *pWal, /* WAL connection */ + int (*xBusy)(void*), /* Function to call when busy */ + void *pBusyArg, /* Context argument for xBusyHandler */ + int lockIdx, /* Offset of first byte to lock */ + int n /* Number of bytes to lock */ +){ + int rc; + do { + rc = walLockExclusive(pWal, lockIdx, n); + }while( xBusy && rc==SQLITE_BUSY && xBusy(pBusyArg) ); + return rc; +} + +/* ** Copy as much content as we can from the WAL back into the database file ** in response to an sqlite3_wal_checkpoint() request or the equivalent. ** @@ -1556,6 +1576,8 @@ static int walIteratorInit(Wal *pWal, WalIterator **pp){ */ static int walCheckpoint( Wal *pWal, /* Wal connection */ + int (*xBusy)(void*), /* Function to call when busy */ + void *pBusyArg, /* Context argument for xBusyHandler */ int sync_flags, /* Flags for OsSync() (or 0) */ int nBuf, /* Size of zBuf in bytes */ u8 *zBuf /* Temporary buffer to use */ @@ -1593,27 +1615,29 @@ static int walCheckpoint( ** 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; - walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); - }else if( rc==SQLITE_BUSY ){ - mxSafeFrame = y; - }else{ - goto walcheckpoint_out; + do { + 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; + walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1); + }else if( rc==SQLITE_BUSY ){ + mxSafeFrame = y; + }else{ + goto walcheckpoint_out; + } } } - } + }while( xBusy && mxSafeFrame<pWal->hdr.mxFrame && xBusy(pBusyArg) ); if( pInfo->nBackfill<mxSafeFrame - && (rc = walLockExclusive(pWal, WAL_READ_LOCK(0), 1))==SQLITE_OK + && (rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(0), 1))==SQLITE_OK ){ i64 nSize; /* Current size of database file */ u32 nBackfill = pInfo->nBackfill; @@ -1666,10 +1690,19 @@ static int walCheckpoint( /* Release the reader lock held while backfilling */ walUnlockExclusive(pWal, WAL_READ_LOCK(0), 1); - }else if( rc==SQLITE_BUSY ){ + + if( xBusy && rc==SQLITE_OK && pWal->hdr.mxFrame==mxSafeFrame ){ + assert( pWal->writeLock ); + rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_READ_LOCK(1), WAL_NREADER-1); + if( rc==SQLITE_OK ){ + walUnlockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1); + } + } + } + + if( rc==SQLITE_BUSY ){ /* Reset the return code so as not to report a checkpoint failure - ** just because active readers prevent any backfill. - */ + ** just because there are active readers. */ rc = SQLITE_OK; } @@ -1704,7 +1737,7 @@ int sqlite3WalClose( if( pWal->exclusiveMode==WAL_NORMAL_MODE ){ pWal->exclusiveMode = WAL_EXCLUSIVE_MODE; } - rc = sqlite3WalCheckpoint(pWal, sync_flags, nBuf, zBuf); + rc = sqlite3WalCheckpoint(pWal, 0, 0, sync_flags, nBuf, zBuf); if( rc==SQLITE_OK ){ isDelete = 1; } @@ -2619,9 +2652,14 @@ int sqlite3WalFrames( ** ** Obtain a CHECKPOINT lock and then backfill as much information as ** we can from WAL into the database. +** +** If parameter xBusy is not NULL, it is a pointer to a busy-handler +** callback. In this case this function runs a blocking checkpoint. */ int sqlite3WalCheckpoint( Wal *pWal, /* Wal connection */ + int (*xBusy)(void*), /* Function to call when busy */ + void *pBusyArg, /* Context argument for xBusyHandler */ int sync_flags, /* Flags to sync db file with (or 0) */ int nBuf, /* Size of temporary buffer */ u8 *zBuf /* Temporary buffer to use */ @@ -2630,6 +2668,7 @@ int sqlite3WalCheckpoint( int isChanged = 0; /* True if a new wal-index header is loaded */ assert( pWal->ckptLock==0 ); + assert( pWal->writeLock==0 ); WALTRACE(("WAL%p: checkpoint begins\n", pWal)); rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1); @@ -2641,10 +2680,21 @@ int sqlite3WalCheckpoint( } pWal->ckptLock = 1; + /* If this is a blocking-checkpoint, then obtain the write-lock as well + ** to prevent any writers from running while the checkpoint is underway. + ** This has to be done before the call to walIndexReadHdr() below. + */ + if( xBusy ){ + rc = walBusyLock(pWal, xBusy, pBusyArg, WAL_WRITE_LOCK, 1); + if( rc==SQLITE_OK ) pWal->writeLock = 1; + } + /* Copy data from the log to the database file. */ - rc = walIndexReadHdr(pWal, &isChanged); if( rc==SQLITE_OK ){ - rc = walCheckpoint(pWal, sync_flags, nBuf, zBuf); + rc = walIndexReadHdr(pWal, &isChanged); + } + if( rc==SQLITE_OK ){ + rc = walCheckpoint(pWal, xBusy, pBusyArg, sync_flags, nBuf, zBuf); } if( isChanged ){ /* If a new wal-index header was loaded before the checkpoint was @@ -2657,6 +2707,7 @@ int sqlite3WalCheckpoint( } /* Release the locks. */ + sqlite3WalEndWriteTransaction(pWal); walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1); pWal->ckptLock = 0; WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok")); |