}else if( pLog->isWriteLocked ){
    logLockRegion(pLog, LOG_REGION_C|LOG_REGION_D, LOG_UNLOCK);
    memcpy(&pLog->hdr, pLog->pSummary->aData, sizeof(pLog->hdr));
    pLog->isWriteLocked = 0;
  }
  return SQLITE_OK;
}




























/* 
** Return true if data has been written but not committed to the log file. 
*/
int sqlite3LogDirty(Log *pLog){
  assert( pLog->isWriteLocked );
  return( pLog->hdr.iLastPg!=((LogSummaryHdr*)pLog->pSummary->aData)->iLastPg );

  }else if( pLog->isWriteLocked ){
    logLockRegion(pLog, LOG_REGION_C|LOG_REGION_D, LOG_UNLOCK);
    memcpy(&pLog->hdr, pLog->pSummary->aData, sizeof(pLog->hdr));
    pLog->isWriteLocked = 0;
  }
  return SQLITE_OK;
}

/*
** The log handle passed to this function must be holding the write-lock.
**
** If any data has been written (but not committed) to the log file, this
** function moves the write-pointer back to the start of the transaction.
**
** Additionally, the callback function is invoked for each frame written
** to the log since the start of the transaction. If the callback returns
** other than SQLITE_OK, it is not invoked again and the error code is
** returned to the caller.
**
** Otherwise, if the callback function does not return an error, this
** function returns SQLITE_OK.
*/
int sqlite3LogUndo(Log *pLog, int (*xUndo)(void *, Pgno), void *pUndoCtx){
  int rc = SQLITE_OK;
  Pgno iMax = pLog->hdr.iLastPg;
  Pgno iFrame;

  assert( pLog->isWriteLocked );
  logSummaryReadHdr(pLog, 0);
  for(iFrame=pLog->hdr.iLastPg+1; iFrame<=iMax && rc==SQLITE_OK; iFrame++){
    rc = xUndo(pUndoCtx, pLog->pSummary->aData[logSummaryEntry(iFrame)]);
  }
  return rc;
}

/* 
** Return true if data has been written but not committed to the log file. 
*/
int sqlite3LogDirty(Log *pLog){
  assert( pLog->isWriteLocked );
  return( pLog->hdr.iLastPg!=((LogSummaryHdr*)pLog->pSummary->aData)->iLastPg );

/* Read a page from the log, if it is present. */
int sqlite3LogRead(Log *pLog, Pgno pgno, int *pInLog, u8 *pOut);
void sqlite3LogDbsize(Log *pLog, Pgno *pPgno);

/* Obtain or release the WRITER lock. */
int sqlite3LogWriteLock(Log *pLog, int op);




/* Return true if data has been written but not committed to the log file. */
int sqlite3LogDirty(Log *pLog);

/* Write a frame or frames to the log. */
int sqlite3LogFrames(Log *pLog, int, PgHdr *, Pgno, int, int);

/* Copy pages from the log to the database file */ 

/* Read a page from the log, if it is present. */
int sqlite3LogRead(Log *pLog, Pgno pgno, int *pInLog, u8 *pOut);
void sqlite3LogDbsize(Log *pLog, Pgno *pPgno);

/* Obtain or release the WRITER lock. */
int sqlite3LogWriteLock(Log *pLog, int op);

/* Undo any frames written (but not committed) to the log */
int sqlite3LogUndo(Log *pLog, int (*xUndo)(void *, Pgno), void *pUndoCtx);

/* Return true if data has been written but not committed to the log file. */
int sqlite3LogDirty(Log *pLog);

/* Write a frame or frames to the log. */
int sqlite3LogFrames(Log *pLog, int, PgHdr *, Pgno, int, int);

/* Copy pages from the log to the database file */ 

  PAGERTRACE(("FETCH %d page %d hash(%08x)\n",
               PAGERID(pPager), pgno, pager_pagehash(pPg)));

  return rc;
}

/*
** This function is called when a transaction on a WAL database is rolled
** back. For each dirty page in the cache, do one of the following:


**
**   * If the page has no outstanding references, simply discard it.
**   * Otherwise, if the page has one or more outstanding references, 



**     reload the original content from the database (or log file).

*/
static int pagerRollbackLog(Pager *pPager){

  int rc = SQLITE_OK;
  PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);


























  /* Normally, if a transaction is rolled back, any backup processes are
  ** updated as data is copied out of the rollback journal and into the
  ** database. This is not generally possible with a WAL database, as
  ** rollback involves simply truncating the log file. Therefore, if one
  ** or more frames have already been written to the log (and therefore 
  ** also copied into the backup databases) as part of this transaction,
  ** the backups must be restarted.
  */
  if( sqlite3LogDirty(pPager->pLog) ){
    sqlite3BackupRestart(pPager->pBackup);
  }








  pPager->dbSize = pPager->dbOrigSize;


  while( pList && rc==SQLITE_OK ){
    PgHdr *pNext = pList->pDirty;
    if( sqlite3PcachePageRefcount(pList)==0 ){
      sqlite3PagerLookup(pPager, pList->pgno);
      sqlite3PcacheDrop(pList);
    }else{
      rc = readDbPage(pList);
      if( rc==SQLITE_OK ){
        pPager->xReiniter(pList);
      }
    }
    pList = pNext;
  }

  return rc;
}

/*
** Playback savepoint pSavepoint. Or, if pSavepoint==NULL, then playback
** the entire master journal file. The case pSavepoint==NULL occurs when 
** a ROLLBACK TO command is invoked on a SAVEPOINT that is a transaction 

  PAGERTRACE(("FETCH %d page %d hash(%08x)\n",
               PAGERID(pPager), pgno, pager_pagehash(pPg)));

  return rc;
}

/*
** This function is invoked once for each page that has already been 
** written into the log file when a WAL transaction is rolled back.
** Parameter iPg is the page number of said page. The pCtx argument 
** is actually a pointer to the Pager structure.
**


** If page iPg is present in the cache, and has no outstanding references,
** it is discarded. Otherwise, if there are one or more outstanding
** references, the page content is reloaded from the database. If the
** attempt to reload content from the database is required and fails, 
** return an SQLite error code. Otherwise, SQLITE_OK.
*/

static int pagerUndoCallback(void *pCtx, Pgno iPg){
  int rc = SQLITE_OK;

  Pager *pPager = (Pager *)pCtx;
  PgHdr *pPg;

  pPg = sqlite3PagerLookup(pPager, iPg);
  if( pPg ){
    if( sqlite3PcachePageRefcount(pPg)==1 ){
      sqlite3PcacheDrop(pPg);
    }else{
      rc = readDbPage(pPg);
      if( rc==SQLITE_OK ){
        pPager->xReiniter(pPg);
      }
      sqlite3PagerUnref(pPg);
    }
  }

  return rc;
}

/*
** This function is called to rollback a transaction on a WAL database.
*/
static int pagerRollbackLog(Pager *pPager){
  int rc;                         /* Return Code */
  PgHdr *pList;                   /* List of dirty pages to revert */

  /* Normally, if a transaction is rolled back, any backup processes are
  ** updated as data is copied out of the rollback journal and into the
  ** database. This is not generally possible with a WAL database, as
  ** rollback involves simply truncating the log file. Therefore, if one
  ** or more frames have already been written to the log (and therefore 
  ** also copied into the backup databases) as part of this transaction,
  ** the backups must be restarted.
  */
  if( sqlite3LogDirty(pPager->pLog) ){
    sqlite3BackupRestart(pPager->pBackup);
  }

  /* For all pages in the cache that are currently dirty or have already
  ** been written (but not committed) to the log file, do one of the 
  ** following:
  **
  **   + Discard the cached page (if refcount==0), or
  **   + Reload page content from the database (if refcount>0).
  */
  pPager->dbSize = pPager->dbOrigSize;
  rc = sqlite3LogUndo(pPager->pLog, pagerUndoCallback, (void *)pPager);
  pList = sqlite3PcacheDirtyList(pPager->pPCache);
  while( pList && rc==SQLITE_OK ){
    PgHdr *pNext = pList->pDirty;

    rc = pagerUndoCallback((void *)pPager, pList->pgno);







    pList = pNext;
  }

  return rc;
}

/*
** Playback savepoint pSavepoint. Or, if pSavepoint==NULL, then playback
** the entire master journal file. The case pSavepoint==NULL occurs when 
** a ROLLBACK TO command is invoked on a SAVEPOINT that is a transaction 

} {1 2 3 4 5 6 7 8 9 10 11 12 13 14}
do_test wal-3.3 {
  execsql { ROLLBACK }
  execsql { SELECT * FROM t1 }
} {1 2 3 4 5 6 7 8 9 10 11 12 13 14}
db2 close





do_test wal-4.1 {
  execsql {
    DELETE FROM t1;
    BEGIN;
      INSERT INTO t1 VALUES('a', 'b');
      SAVEPOINT sp;
        INSERT INTO t1 VALUES('c', 'd');
................................................................................
do_test wal-4.3 {
  execsql {
    COMMIT;
    SELECT * FROM t1;
  }
} {a b}




















































do_test wal-5.1 {
  execsql {
    CREATE TEMP TABLE t2(a, b);
    INSERT INTO t2 VALUES(1, 2);
  }
} {}
do_test wal-5.2 {

} {1 2 3 4 5 6 7 8 9 10 11 12 13 14}
do_test wal-3.3 {
  execsql { ROLLBACK }
  execsql { SELECT * FROM t1 }
} {1 2 3 4 5 6 7 8 9 10 11 12 13 14}
db2 close

#-------------------------------------------------------------------------
# The following tests, wal-4.*, test that savepoints work with WAL 
# databases.
#
do_test wal-4.1 {
  execsql {
    DELETE FROM t1;
    BEGIN;
      INSERT INTO t1 VALUES('a', 'b');
      SAVEPOINT sp;
        INSERT INTO t1 VALUES('c', 'd');
................................................................................
do_test wal-4.3 {
  execsql {
    COMMIT;
    SELECT * FROM t1;
  }
} {a b}

do_test wal-4.4 {
  db close
  sqlite3 db test.db
  db func blob blob
  list [execsql { SELECT * FROM t1 }] [file size test.db-wal]
} {{a b} 0}
do_test wal-4.5 {
  execsql { PRAGMA cache_size = 10 }
  execsql {
    CREATE TABLE t2(a, b);
    INSERT INTO t2 VALUES(blob(400), blob(400));
    SAVEPOINT tr;
      INSERT INTO t2 SELECT blob(400), blob(400) FROM t2; /*  2 */
      INSERT INTO t2 SELECT blob(400), blob(400) FROM t2; /*  4 */
      INSERT INTO t2 SELECT blob(400), blob(400) FROM t2; /*  8 */
      INSERT INTO t2 SELECT blob(400), blob(400) FROM t2; /* 16 */
      INSERT INTO t2 SELECT blob(400), blob(400) FROM t2; /* 32 */
      INSERT INTO t1 SELECT blob(400), blob(400) FROM t1; /*  2 */
      INSERT INTO t1 SELECT blob(400), blob(400) FROM t1; /*  4 */
      INSERT INTO t1 SELECT blob(400), blob(400) FROM t1; /*  8 */
      INSERT INTO t1 SELECT blob(400), blob(400) FROM t1; /* 16 */
      INSERT INTO t1 SELECT blob(400), blob(400) FROM t1; /* 32 */
      SELECT count(*) FROM t2;
  }
} {32}
do_test wal-4.6 {
  execsql { ROLLBACK TO tr }
} {}
do_test wal-4.7 {
  set logsize [file size test.db-wal]
  execsql {
      INSERT INTO t1 VALUES('x', 'y');
    RELEASE tr;
  }
  expr { $logsize == [file size test.db-wal] }
} {1}
do_test wal-4.8 {
  execsql { SELECT count(*) FROM t2 }
} {1}
do_test wal-4.9 {
  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3 db2 test2.db
  execsql { SELECT count(*) FROM t2 ; SELECT count(*) FROM t1 } db2
} {1 2}
do_test wal-4.10 {
  execsql { PRAGMA integrity_check } db2
} {ok}
db2 close

reopen_db
do_test wal-5.1 {
  execsql {
    CREATE TEMP TABLE t2(a, b);
    INSERT INTO t2 VALUES(1, 2);
  }
} {}
do_test wal-5.2 {