}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;
}









/* 
** Write a set of frames to the log. The caller must hold at least a
** RESERVED lock on the database file.
*/
int sqlite3LogFrames(
  Log *pLog,                      /* Log handle to write to */

  }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 );
}

/* 
** Write a set of frames to the log. The caller must hold at least a
** RESERVED lock on the database file.
*/
int sqlite3LogFrames(
  Log *pLog,                      /* Log handle to write to */

/* 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);




/* 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 */ 
int sqlite3LogCheckpoint(
  Log *pLog,                      /* Log connection */

/* 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 */ 
int sqlite3LogCheckpoint(
  Log *pLog,                      /* Log connection */

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

  return rc;
}









static int pagerRollbackLog(Pager *pPager){
  int rc = SQLITE_OK;
  PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);













  pPager->dbSize = pPager->dbOrigSize;
  while( pList && rc==SQLITE_OK ){
    PgHdr *pNext = pList->pDirty;
    if( sqlite3PcachePageRefcount(pList)==0 ){
      sqlite3PagerLookup(pPager, pList->pgno);
      sqlite3PcacheDrop(pList);
    }else{
................................................................................
    pPager->nSubRec++;
    assert( pPager->nSavepoint>0 );
    rc = addToSavepointBitvecs(pPager, pPg->pgno);
  }
  return rc;
}





























/*
** This function is called by the pcache layer when it has reached some
** soft memory limit. The first argument is a pointer to a Pager object
** (cast as a void*). The pager is always 'purgeable' (not an in-memory
** database). The second argument is a reference to a page that is 
** currently dirty but has no outstanding references. The page
................................................................................

  assert( pPg->pPager==pPager );
  assert( pPg->flags&PGHDR_DIRTY );

  pPg->pDirty = 0;
  if( pagerUseLog(pPager) ){
    /* Write a single frame for this page to the log. */
    rc = sqlite3LogFrames(pPager->pLog, pPager->pageSize, pPg, 0, 0, 0);
  }else{
    /* The doNotSync flag is set by the sqlite3PagerWrite() function while it
    ** is journalling a set of two or more database pages that are stored
    ** on the same disk sector. Syncing the journal is not allowed while
    ** this is happening as it is important that all members of such a
    ** set of pages are synced to disk together. So, if the page this function
    ** is trying to make clean will require a journal sync and the doNotSync
................................................................................
    ** backup in progress needs to be restarted.
    */
    sqlite3BackupRestart(pPager->pBackup);
  }else if( pPager->state!=PAGER_SYNCED && pPager->dbModified ){
    if( pagerUseLog(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
      if( pList ){
        rc = sqlite3LogFrames(pPager->pLog, pPager->pageSize, pList,
            pPager->dbSize, 1, (pPager->fullSync ? pPager->sync_flags : 0)
        );
      }
      sqlite3PcacheCleanAll(pPager->pPCache);
    }else{
      /* The following block updates the change-counter. Exactly how it
      ** does this depends on whether or not the atomic-update optimization
      ** was enabled at compile time, and if this transaction meets the 
................................................................................
**   hot-journal rollback).
*/
int sqlite3PagerRollback(Pager *pPager){
  int rc = SQLITE_OK;                  /* Return code */
  PAGERTRACE(("ROLLBACK %d\n", PAGERID(pPager)));
  if( pagerUseLog(pPager) ){
    int rc2;

    rc = sqlite3PagerSavepoint(pPager, SAVEPOINT_ROLLBACK, -1);
    rc2 = pager_end_transaction(pPager, pPager->setMaster);
    if( rc==SQLITE_OK ) rc = rc2;
  }else if( !pPager->dbModified || !isOpen(pPager->jfd) ){
    rc = pager_end_transaction(pPager, pPager->setMaster);
  }else if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
    if( pPager->state>=PAGER_EXCLUSIVE ){

  IOTRACE(("PGIN %p %d\n", pPager, pgno));
  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{
................................................................................
    pPager->nSubRec++;
    assert( pPager->nSavepoint>0 );
    rc = addToSavepointBitvecs(pPager, pPg->pgno);
  }
  return rc;
}

/*
** This function is a wrapper around sqlite3LogFrames(). As well as logging
** the contents of the list of pages headed by pList (connected by pDirty),
** this function notifies any active backup processes that the pages have
** changed. 
*/ 
static int pagerLogFrames(
  Pager *pPager,                  /* Pager object */
  PgHdr *pList,                   /* List of frames to log */
  Pgno nTruncate,                 /* Database size after this commit */
  int isCommit,                   /* True if this is a commit */
  int sync_flags                  /* Flags to pass to OsSync() (or 0) */
){
  int rc;                         /* Return code */

  assert( pPager->pLog );
  rc = sqlite3LogFrames(pPager->pLog, 
      pPager->pageSize, pList, nTruncate, isCommit, sync_flags
  );
  if( rc==SQLITE_OK && pPager->pBackup ){
    PgHdr *p;
    for(p=pList; p; p=p->pDirty){
      sqlite3BackupUpdate(pPager->pBackup, p->pgno, (u8 *)p->pData);
    }
  }
  return rc;
}

/*
** This function is called by the pcache layer when it has reached some
** soft memory limit. The first argument is a pointer to a Pager object
** (cast as a void*). The pager is always 'purgeable' (not an in-memory
** database). The second argument is a reference to a page that is 
** currently dirty but has no outstanding references. The page
................................................................................

  assert( pPg->pPager==pPager );
  assert( pPg->flags&PGHDR_DIRTY );

  pPg->pDirty = 0;
  if( pagerUseLog(pPager) ){
    /* Write a single frame for this page to the log. */
    rc = pagerLogFrames(pPager, pPg, 0, 0, 0);
  }else{
    /* The doNotSync flag is set by the sqlite3PagerWrite() function while it
    ** is journalling a set of two or more database pages that are stored
    ** on the same disk sector. Syncing the journal is not allowed while
    ** this is happening as it is important that all members of such a
    ** set of pages are synced to disk together. So, if the page this function
    ** is trying to make clean will require a journal sync and the doNotSync
................................................................................
    ** backup in progress needs to be restarted.
    */
    sqlite3BackupRestart(pPager->pBackup);
  }else if( pPager->state!=PAGER_SYNCED && pPager->dbModified ){
    if( pagerUseLog(pPager) ){
      PgHdr *pList = sqlite3PcacheDirtyList(pPager->pPCache);
      if( pList ){
        rc = pagerLogFrames(pPager, pList, pPager->dbSize, 1, 
            (pPager->fullSync ? pPager->sync_flags : 0)
        );
      }
      sqlite3PcacheCleanAll(pPager->pPCache);
    }else{
      /* The following block updates the change-counter. Exactly how it
      ** does this depends on whether or not the atomic-update optimization
      ** was enabled at compile time, and if this transaction meets the 
................................................................................
**   hot-journal rollback).
*/
int sqlite3PagerRollback(Pager *pPager){
  int rc = SQLITE_OK;                  /* Return code */
  PAGERTRACE(("ROLLBACK %d\n", PAGERID(pPager)));
  if( pagerUseLog(pPager) ){
    int rc2;

    rc = sqlite3PagerSavepoint(pPager, SAVEPOINT_ROLLBACK, -1);
    rc2 = pager_end_transaction(pPager, pPager->setMaster);
    if( rc==SQLITE_OK ) rc = rc2;
  }else if( !pPager->dbModified || !isOpen(pPager->jfd) ){
    rc = pager_end_transaction(pPager, pPager->setMaster);
  }else if( pPager->errCode && pPager->errCode!=SQLITE_FULL ){
    if( pPager->state>=PAGER_EXCLUSIVE ){

#
# backup-7.*: Test SQLITE_BUSY and SQLITE_LOCKED errors.
#
# backup-8.*: Test multiple simultaneous backup operations.
#
# backup-9.*: Test that passing a negative argument to backup_step() is
#             interpreted as "copy the whole file".


#

proc data_checksum {db file} { $db one "SELECT md5sum(a, b) FROM ${file}.t1" }
proc test_contents {name db1 file1 db2 file2} {
  $db2 eval {select * from sqlite_master}
  $db1 eval {select * from sqlite_master}
  set checksum [data_checksum $db2 $file2]
................................................................................
  } {ok}

  db2 close
  db3 close
}



# Test that if the database is written to via the same database handle being
# used as the source by a backup operation:
#
#   10.1.*: If the db is in-memory, the backup is restarted.
#   10.2.*: If the db is a file, the backup is not restarted.
#
db close

#
# backup-7.*: Test SQLITE_BUSY and SQLITE_LOCKED errors.
#
# backup-8.*: Test multiple simultaneous backup operations.
#
# backup-9.*: Test that passing a negative argument to backup_step() is
#             interpreted as "copy the whole file".
# 
# backup-10.*: Test writing the source database mid backup.
#

proc data_checksum {db file} { $db one "SELECT md5sum(a, b) FROM ${file}.t1" }
proc test_contents {name db1 file1 db2 file2} {
  $db2 eval {select * from sqlite_master}
  $db1 eval {select * from sqlite_master}
  set checksum [data_checksum $db2 $file2]
................................................................................
  } {ok}

  db2 close
  db3 close
}


#-----------------------------------------------------------------------
# Test that if the database is written to via the same database handle being
# used as the source by a backup operation:
#
#   10.1.*: If the db is in-memory, the backup is restarted.
#   10.2.*: If the db is a file, the backup is not restarted.
#
db close

set testdir [file dirname $argv0]
source $testdir/tester.tcl

proc log_file_size {nFrame pgsz} {
  expr {12 + ($pgsz+16)*$nFrame}
}







# Make sure a simple backup from a WAL database works.
#
do_test walbak-1.0 {
  execsql { 
    PRAGMA synchronous = NORMAL;
    PRAGMA page_size = 1024;
................................................................................
do_test walbak-1.3 {
  execsql { PRAGMA integrity_check } db2
} {ok}
db2 close

# Try a VACUUM on a WAL database.
#
do_test walbak-2.1 {
  execsql { 
    VACUUM;
    PRAGMA main.journal_mode;
  }
} {wal}
do_test walbak-2.2 {
  list [file size test.db] [file size test.db-wal]
} [list 1024 [log_file_size 6 1024]]
do_test walbak-2.3 {
  execsql { PRAGMA checkpoint }
  list [file size test.db] [file size test.db-wal]
} [list [expr 3*1024] [log_file_size 6 1024]]
do_test walbak-2.4 {
  execsql { 
    CREATE TABLE t2(a, b);
    INSERT INTO t2 SELECT * FROM t1;
    DROP TABLE t1;
  }
  list [file size test.db] [file size test.db-wal]
} [list [expr 3*1024] [log_file_size 6 1024]]
do_test walbak-2.5 {
  execsql { VACUUM }
  list [file size test.db] [file size test.db-wal]
} [list [expr 3*1024] [log_file_size 8 1024]]
do_test walbak-2.6 {
  execsql { PRAGMA checkpoint }
  list [file size test.db] [file size test.db-wal]
} [list [expr 2*1024] [log_file_size 8 1024]]




























































































finish_test

set testdir [file dirname $argv0]
source $testdir/tester.tcl

proc log_file_size {nFrame pgsz} {
  expr {12 + ($pgsz+16)*$nFrame}
}

# Test organization:
# 
#   walback-1.*: Simple tests.
#   walback-2.*: Test backups when the source db is modified mid-backup.
#

# Make sure a simple backup from a WAL database works.
#
do_test walbak-1.0 {
  execsql { 
    PRAGMA synchronous = NORMAL;
    PRAGMA page_size = 1024;
................................................................................
do_test walbak-1.3 {
  execsql { PRAGMA integrity_check } db2
} {ok}
db2 close

# Try a VACUUM on a WAL database.
#
do_test walbak-1.4 {
  execsql { 
    VACUUM;
    PRAGMA main.journal_mode;
  }
} {wal}
do_test walbak-1.5 {
  list [file size test.db] [file size test.db-wal]
} [list 1024 [log_file_size 6 1024]]
do_test walbak-1.6 {
  execsql { PRAGMA checkpoint }
  list [file size test.db] [file size test.db-wal]
} [list [expr 3*1024] [log_file_size 6 1024]]
do_test walbak-1.7 {
  execsql { 
    CREATE TABLE t2(a, b);
    INSERT INTO t2 SELECT * FROM t1;
    DROP TABLE t1;
  }
  list [file size test.db] [file size test.db-wal]
} [list [expr 3*1024] [log_file_size 6 1024]]
do_test walbak-1.8 {
  execsql { VACUUM }
  list [file size test.db] [file size test.db-wal]
} [list [expr 3*1024] [log_file_size 8 1024]]
do_test walbak-1.9 {
  execsql { PRAGMA checkpoint }
  list [file size test.db] [file size test.db-wal]
} [list [expr 2*1024] [log_file_size 8 1024]]

#-------------------------------------------------------------------------
# Backups when the source db is modified mid-backup.
#
proc sig {{db db}} {
  $db eval { 
    PRAGMA integrity_check;
    SELECT md5sum(a, b) FROM t1; 
  }
}
db close
file delete test.db
sqlite3 db test.db
do_test walbak-2.1 {
  execsql { PRAGMA journal_mode = WAL }
  execsql {
    CREATE TABLE t1(a PRIMARY KEY, b);
    BEGIN;
      INSERT INTO t1 VALUES(randomblob(500), randomblob(500));
      INSERT INTO t1 SELECT randomblob(500), randomblob(500) FROM t1; /*  2 */
      INSERT INTO t1 SELECT randomblob(500), randomblob(500) FROM t1; /*  4 */
      INSERT INTO t1 SELECT randomblob(500), randomblob(500) FROM t1; /*  8 */
      INSERT INTO t1 SELECT randomblob(500), randomblob(500) FROM t1; /* 16 */
      INSERT INTO t1 SELECT randomblob(500), randomblob(500) FROM t1; /* 32 */
      INSERT INTO t1 SELECT randomblob(500), randomblob(500) FROM t1; /* 64 */
    COMMIT;
  }
} {}
do_test walbak-2.2 {
  db backup abc.db
  sqlite3 db2 abc.db
  string compare [sig db] [sig db2]
} {0}

do_test walbak-2.3 {
  sqlite3_backup B db2 main db main
  B step 50
  execsql { UPDATE t1 SET b = randomblob(500) }
  list [B step 1000] [B finish]
} {SQLITE_DONE SQLITE_OK}
do_test walbak-2.4 {
  string compare [sig db] [sig db2]
} {0}

do_test walbak-2.5 {
  db close
  sqlite3 db test.db
  execsql { PRAGMA cache_size = 10 }
  sqlite3_backup B db2 main db main
  B step 50
  execsql {
    BEGIN;
      UPDATE t1 SET b = randomblob(500);
  }
  expr [file size test.db-wal] > 10*1024
} {1}
do_test walbak-2.6 {
  B step 1000
} {SQLITE_BUSY}
do_test walbak-2.7 {
  execsql COMMIT
  list [B step 1000] [B finish]
} {SQLITE_DONE SQLITE_OK}
do_test walbak-2.8 {
  string compare [sig db] [sig db2]
} {0}

do_test walbak-2.9 {
  db close
  sqlite3 db test.db
  execsql { PRAGMA cache_size = 10 }
  sqlite3_backup B db2 main db main
  B step 50
  execsql {
    BEGIN;
      UPDATE t1 SET b = randomblob(500);
  }
  expr [file size test.db-wal] > 10*1024
} {1}
do_test walbak-2.10 {
  B step 1000
} {SQLITE_BUSY}
do_test walbak-2.11 {
  execsql ROLLBACK
set sigB [sig db]
  list [B step 1000] [B finish]
} {SQLITE_DONE SQLITE_OK}
do_test walbak-2.12 {
  string compare [sig db] [sig db2]
} {0}
db2 close

finish_test