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+/*
+** 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.
+*/
+
+#ifndef _WAL_H_
+#define _WAL_H_
+
+#include "sqliteInt.h"
+
+#ifdef SQLITE_OMIT_WAL
+# define sqlite3WalOpen(x,y,z) 0
+# define sqlite3WalLimit(x,y)
+# define sqlite3WalClose(w,x,y,z) 0
+# define sqlite3WalBeginReadTransaction(y,z) 0
+# define sqlite3WalEndReadTransaction(z)
+# define sqlite3WalRead(v,w,x,y,z) 0
+# define sqlite3WalDbsize(y) 0
+# define sqlite3WalBeginWriteTransaction(y) 0
+# define sqlite3WalEndWriteTransaction(x) 0
+# define sqlite3WalUndo(x,y,z) 0
+# define sqlite3WalSavepoint(y,z)
+# define sqlite3WalSavepointUndo(y,z) 0
+# define sqlite3WalFrames(u,v,w,x,y,z) 0
+# define sqlite3WalCheckpoint(r,s,t,u,v,w,x,y,z) 0
+# define sqlite3WalCallback(z) 0
+# define sqlite3WalExclusiveMode(y,z) 0
+# define sqlite3WalHeapMemory(z) 0
+#else
+
+#define WAL_SAVEPOINT_NDATA 4
+
+/* Connection to a write-ahead log (WAL) file.
+** There is one object of this type for each pager.
+*/
+typedef struct Wal Wal;
+
+/* Open and close a connection to a write-ahead log. */
+int sqlite3WalOpen(sqlite3_vfs*, sqlite3_file*, const char *, int, i64, Wal**);
+int sqlite3WalClose(Wal *pWal, int sync_flags, int, u8 *);
+
+/* Set the limiting size of a WAL file. */
+void sqlite3WalLimit(Wal*, i64);
+
+/* 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 *);
+void sqlite3WalEndReadTransaction(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);
+
+/* If the WAL is not empty, return the size of the database. */
+Pgno sqlite3WalDbsize(Wal *pWal);
+
+/* Obtain or release the WRITER lock. */
+int sqlite3WalBeginWriteTransaction(Wal *pWal);
+int sqlite3WalEndWriteTransaction(Wal *pWal);
+
+/* Undo any frames written (but not committed) to the log */
+int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx);
+
+/* Return an integer that records the current (uncommitted) write
+** position in the WAL */
+void sqlite3WalSavepoint(Wal *pWal, u32 *aWalData);
+
+/* Move the write position of the WAL back to iFrame. Called in
+** response to a ROLLBACK TO command. */
+int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData);
+
+/* Write a frame or frames to the log. */
+int sqlite3WalFrames(Wal *pWal, int, PgHdr *, Pgno, int, int);
+
+/* Copy pages from the log to the database file */
+int sqlite3WalCheckpoint(
+ Wal *pWal, /* Write-ahead log connection */
+ int eMode, /* One of PASSIVE, FULL and RESTART */
+ 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 buffer nBuf */
+ u8 *zBuf, /* Temporary buffer to use */
+ int *pnLog, /* OUT: Number of frames in WAL */
+ int *pnCkpt /* OUT: Number of backfilled frames in WAL */
+);
+
+/* 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(Wal *pWal);
+
+/* Tell the wal layer that an EXCLUSIVE lock has been obtained (or released)
+** by the pager layer on the database file.
+*/
+int sqlite3WalExclusiveMode(Wal *pWal, int op);
+
+/* Return true if the argument is non-NULL and the WAL module is using
+** heap-memory for the wal-index. Otherwise, if the argument is NULL or the
+** WAL module is using shared-memory, return false.
+*/
+int sqlite3WalHeapMemory(Wal *pWal);
+
+#endif /* ifndef SQLITE_OMIT_WAL */
+#endif /* _WAL_H_ */