— part of check-in
on branch wal
— Rename the sqlite3_log_hook() to sqlite3_wal_hook(). Added comments to
** 2010 February 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 header file defines the interface to the write-ahead logging
** system. Refer to the comments below and the header comment attached to
** the implementation of each function in log.c for further details.
/* Connection to a write-ahead log (WAL) file.
** There is one object of this type for each pager.
typedef struct Log Log;
/* Open and close a connection to a write-ahead log. */
int sqlite3WalOpen(sqlite3_vfs*, const char *zDb, Log **ppLog);
int sqlite3WalClose(Log *pLog, sqlite3_file *pFd, int sync_flags, u8 *zBuf);
/* 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
** transaction and releases the lock.
int sqlite3WalOpenSnapshot(Log *pLog, int *);
void sqlite3WalCloseSnapshot(Log *pLog);
/* Read a page from the write-ahead log, if it is present. */
int sqlite3WalRead(Log *pLog, Pgno pgno, int *pInLog, u8 *pOut);
/* Return the size of the database as it existed at the beginning
** of the snapshot */
void sqlite3WalDbsize(Log *pLog, Pgno *pPgno);
/* Obtain or release the WRITER lock. */
int sqlite3WalWriteLock(Log *pLog, int op);
/* Undo any frames written (but not committed) to the log */
int sqlite3WalUndo(Log *pLog, int (*xUndo)(void *, Pgno), void *pUndoCtx);
/* Return an integer that records the current (uncommitted) write
** position in the WAL */
u32 sqlite3WalSavepoint(Log *pLog);
/* Move the write position of the WAL back to iFrame. Called in
** response to a ROLLBACK TO command. */
int sqlite3WalSavepointUndo(Log *pLog, u32 iFrame);
/* Return true if data has been written but not committed to the log file. */
int sqlite3WalDirty(Log *pLog);
/* Write a frame or frames to the log. */
int sqlite3WalFrames(Log *pLog, int, PgHdr *, Pgno, int, int);
/* Copy pages from the log to the database file */
Log *pLog, /* Log connection */
sqlite3_file *pFd, /* File descriptor open on db file */
int sync_flags, /* Flags to sync db file with (or 0) */
u8 *zBuf, /* Temporary buffer to use */
int (*xBusyHandler)(void *), /* Pointer to busy-handler function */
void *pBusyHandlerArg /* Argument to pass to xBusyHandler */
/* Return the value to pass to a sqlite3_wal_hook callback, the
** number of frames in the WAL at the point of the last commit since
** sqlite3WalCallback() was called. If no commits have occurred since
** the last call, then return 0.
int sqlite3WalCallback(Log *pLog);
#endif /* _WAL_H_ */