/* Undo any frames written (but not committed) to the log */
int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx);
/* Obtain or release the WRITER lock. */
int sqlite3WalBeginWriteTransaction(Wal *pWal);
int sqlite3WalEndWriteTransaction(Wal *pWal);
/* If the WAL is not empty, return the size of the database. */
Pgno sqlite3WalDbsize(Wal *pWal);
/* Read a page from the write-ahead log, if it is present. */
int sqlite3WalRead(Wal *pWal, Pgno pgno, int *pInWal, int nOut, u8 *pOut);
void sqlite3WalEndReadTransaction(Wal *pWal);
/* 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 sqlite3WalBeginReadTransaction(Wal *pWal, int *);
int sqlite3WalClose(Wal *pWal, int sync_flags, int, u8 *);
