if( page1[18]>2 ){
      pBt->readOnly = 1;
    }
    if( page1[19]>2 ){
      goto page1_init_failed;
    }

    /* If the write version is set to 2, turn on write-ahead logging mode. */







    if( page1[19]==2 ){
      int isOpen = 0;
      rc = sqlite3PagerOpenLog(pBt->pPager, &isOpen);
      if( rc!=SQLITE_OK ){
        goto page1_init_failed;
      }else if( isOpen==0 ){
        releasePage(pPage1);

    if( page1[18]>2 ){
      pBt->readOnly = 1;
    }
    if( page1[19]>2 ){
      goto page1_init_failed;
    }

    /* If the write version is set to 2, this database should be accessed
    ** in WAL mode. If the log is not already open, open it now. Then 
    ** return SQLITE_OK and return without populating BtShared.pPage1.
    ** The caller detects this and calls this function again. This is
    ** required as the version of page 1 currently in the page1 buffer
    ** may not be the latest version - there may be a newer one in the log
    ** file.
    */
    if( page1[19]==2 ){
      int isOpen = 0;
      rc = sqlite3PagerOpenLog(pBt->pPager, &isOpen);
      if( rc!=SQLITE_OK ){
        goto page1_init_failed;
      }else if( isOpen==0 ){
        releasePage(pPage1);

  /* The changeCountDone flag is always set for temp-files */
  assert( pPager->tempFile==0 || pPager->changeCountDone );

  return 1;
}
#endif












/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
** or more open savepoints for which:
**
**   * The page-number is less than or equal to PagerSavepoint.nOrig, and
................................................................................
      }
    }
  }

  return rc;
}























































/*
** This function is called to obtain a shared lock on the database file.
** It is illegal to call sqlite3PagerAcquire() until after this function
** has been successfully called. If a shared-lock is already held when
** this function is called, it is a no-op.
**
................................................................................
      isErrorReset = 1;
    }
    pPager->errCode = SQLITE_OK;
    pager_reset(pPager);
  }

  if( pagerUseLog(pPager) ){
    int changed = 0;              /* True if the cache must be flushed */

    /* Open a log snapshot to read from. */
    rc = sqlite3LogOpenSnapshot(pPager->pLog, &changed);
    if( rc==SQLITE_OK ){
      int dummy;
      if( changed ){
        pager_reset(pPager);
        assert( pPager->errCode || pPager->dbSizeValid==0 );
      }
      rc = sqlite3PagerPagecount(pPager, &dummy);
    }
    pPager->state = PAGER_SHARED;

  }else if( pPager->state==PAGER_UNLOCK || isErrorReset ){
    sqlite3_vfs * const pVfs = pPager->pVfs;
    int isHotJournal = 0;

    assert( !MEMDB );
    assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
    if( pPager->noReadlock ){
      assert( pPager->readOnly );
      pPager->state = PAGER_SHARED;
    }else{
      rc = pager_wait_on_lock(pPager, SHARED_LOCK);
................................................................................

      if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
        pager_reset(pPager);
      }
    }
    assert( pPager->exclusiveMode || pPager->state==PAGER_SHARED );











    if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
      pPager->journalMode = PAGER_JOURNALMODE_DELETE;
    }
  }

 failed:
  if( rc!=SQLITE_OK ){
    /* pager_unlock() is a no-op for exclusive mode and in-memory databases. */
................................................................................
**
** The caller must be holding a SHARED lock on the database file to call
** this function.
*/
int sqlite3PagerOpenLog(Pager *pPager, int *pisOpen){
  int rc = SQLITE_OK;             /* Return code */

#ifdef SQLITE_DEBUG
  int locktype;
  sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_LOCKSTATE, &locktype);
  assert( locktype==SQLITE_LOCK_SHARED );
  assert( pPager->state>=PAGER_SHARED );
#endif

  if( !pPager->pLog ){

    /* Open the connection to the log file. If this operation fails, 
    ** (e.g. due to malloc() failure), unlock the database file and 
    ** return an error code.
    */
    rc = sqlite3LogOpen(pPager->pVfs, pPager->zFilename, &pPager->pLog);
................................................................................
      rc = sqlite3LogClose(pPager->pLog, pPager->fd,
        (pPager->noSync ? 0 : pPager->sync_flags), 
        (u8*)pPager->pTmpSpace
      );
      pPager->pLog = 0;
    }

    /* Make sure the EXCLUSIVE lock has not been lost somehow */
#ifdef SQLITE_DEBUG
    {
      int locktype;
      sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_LOCKSTATE, &locktype);
      assert( locktype==SQLITE_LOCK_EXCLUSIVE );
    }
#endif

  }
  return rc;
}

#endif /* SQLITE_OMIT_DISKIO */

  /* The changeCountDone flag is always set for temp-files */
  assert( pPager->tempFile==0 || pPager->changeCountDone );

  return 1;
}
#endif

#ifndef NDEBUG 
static void assert_file_lock(Pager *pPager, int eLock){
  int locktype;
  sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_LOCKSTATE, &locktype);
  assert( locktype==eLock );
}
#else
# define assert_file_lock(x,y) 
#endif


/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
** or more open savepoints for which:
**
**   * The page-number is less than or equal to PagerSavepoint.nOrig, and
................................................................................
      }
    }
  }

  return rc;
}

/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists. Assuming no error occurs, set *pExists to 1 if the file exists,
** or 0 otherwise and return SQLITE_OK. If an IO or OOM error occurs, return
** an SQLite error code.
**
** The caller must hold a SHARED lock on the database file to call this
** function.
*/
static int pagerHasWAL(Pager *pPager, int *pExists){
  int rc;                         /* Return code */

  /* Check that a SHARED lock is held on the database file. Because an
  ** EXCLUSIVE lock on the db file is required to delete a WAL, this
  ** ensures there is no race condition between the xAccess() below and
  ** an xDelete() being executed by some other connection.
  */
  assert_file_lock(pPager, SQLITE_LOCK_SHARED);

  if( !pPager->tempFile ){
    char *zLog = sqlite3_mprintf("%s-wal", pPager->zFilename);
    if( !zLog ){
      rc = SQLITE_NOMEM;
    }else{
      rc = sqlite3OsAccess(pPager->pVfs, zLog, SQLITE_ACCESS_EXISTS, pExists);
      sqlite3_free(zLog);
    }
  }else{
    rc = SQLITE_OK;
    *pExists = 0;
  }
  return rc;
}

static int pagerOpenSnapshot(Pager *pPager){
  int rc;
  int changed;

  assert( pagerUseLog(pPager) );

  rc = sqlite3LogOpenSnapshot(pPager->pLog, &changed);
  if( rc==SQLITE_OK ){
    int dummy;
    if( changed ){
        pager_reset(pPager);
        assert( pPager->errCode || pPager->dbSizeValid==0 );
    }
    rc = sqlite3PagerPagecount(pPager, &dummy);
  }
  pPager->state = PAGER_SHARED;

  return rc;
}

/*
** This function is called to obtain a shared lock on the database file.
** It is illegal to call sqlite3PagerAcquire() until after this function
** has been successfully called. If a shared-lock is already held when
** this function is called, it is a no-op.
**
................................................................................
      isErrorReset = 1;
    }
    pPager->errCode = SQLITE_OK;
    pager_reset(pPager);
  }

  if( pagerUseLog(pPager) ){



    rc = pagerOpenSnapshot(pPager);










  }else if( pPager->state==PAGER_UNLOCK || isErrorReset ){
    sqlite3_vfs * const pVfs = pPager->pVfs;
    int isHotJournal = 0;
    int isWal = 0;
    assert( !MEMDB );
    assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
    if( pPager->noReadlock ){
      assert( pPager->readOnly );
      pPager->state = PAGER_SHARED;
    }else{
      rc = pager_wait_on_lock(pPager, SHARED_LOCK);
................................................................................

      if( memcmp(pPager->dbFileVers, dbFileVers, sizeof(dbFileVers))!=0 ){
        pager_reset(pPager);
      }
    }
    assert( pPager->exclusiveMode || pPager->state==PAGER_SHARED );

    rc = pagerHasWAL(pPager, &isWal);
    if( rc!=SQLITE_OK ){
      goto failed;
    }
    if( isWal ){
      pager_reset(pPager);
      rc = sqlite3PagerOpenLog(pPager, 0);
      if( rc==SQLITE_OK ){
        rc = pagerOpenSnapshot(pPager);
      }
    }else if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
      pPager->journalMode = PAGER_JOURNALMODE_DELETE;
    }
  }

 failed:
  if( rc!=SQLITE_OK ){
    /* pager_unlock() is a no-op for exclusive mode and in-memory databases. */
................................................................................
**
** The caller must be holding a SHARED lock on the database file to call
** this function.
*/
int sqlite3PagerOpenLog(Pager *pPager, int *pisOpen){
  int rc = SQLITE_OK;             /* Return code */




  assert_file_lock(pPager, SQLITE_LOCK_SHARED);



  if( !pPager->pLog ){

    /* Open the connection to the log file. If this operation fails, 
    ** (e.g. due to malloc() failure), unlock the database file and 
    ** return an error code.
    */
    rc = sqlite3LogOpen(pPager->pVfs, pPager->zFilename, &pPager->pLog);
................................................................................
      rc = sqlite3LogClose(pPager->pLog, pPager->fd,
        (pPager->noSync ? 0 : pPager->sync_flags), 
        (u8*)pPager->pTmpSpace
      );
      pPager->pLog = 0;
    }






    assert_file_lock(pPager, SQLITE_LOCK_EXCLUSIVE);



  }
  return rc;
}

#endif /* SQLITE_OMIT_DISKIO */

  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 1}
db2 close

file copy -force test.db-wal A
do_test wal-12.5 {
  execsql {
    PRAGMA checkpoint;
    UPDATE t2 SET y = 2 WHERE x = 'B'; 
    PRAGMA checkpoint;
    UPDATE t1 SET y = 1 WHERE x = 'A';
    PRAGMA checkpoint;
    UPDATE t1 SET y = 0 WHERE x = 'A';
    SELECT * FROM t2;
  }
} {B 2}
file copy -force test.db-wal B

do_test wal-12.4 {
  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 2}
db2 close

finish_test

  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 1}
db2 close


do_test wal-12.5 {
  execsql {
    PRAGMA checkpoint;
    UPDATE t2 SET y = 2 WHERE x = 'B'; 
    PRAGMA checkpoint;
    UPDATE t1 SET y = 1 WHERE x = 'A';
    PRAGMA checkpoint;
    UPDATE t1 SET y = 0 WHERE x = 'A';
    SELECT * FROM t2;
  }
} {B 2}


do_test wal-12.4 {
  file copy -force test.db test2.db
  file copy -force test.db-wal test2.db-wal
  sqlite3_wal db2 test2.db
  execsql { SELECT * FROM t2 } db2
} {B 2}
db2 close

finish_test

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

set seed 0
set REPEATS 100

proc sqlite3_wal {args} {
  eval sqlite3 $args
  [lindex $args 0] eval { PRAGMA journal_mode = wal }
}

# walcrash-1.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
  file delete -force test.db test.db-wal
  do_test walcrash-1.$i.1 {
    crashsql -delay 4 -file test.db-wal -seed [incr seed] {
      PRAGMA journal_mode = WAL;
................................................................................
      CREATE TABLE t1(a, b);
      INSERT INTO t1 VALUES(1, 1);
      INSERT INTO t1 VALUES(2, 3);
      INSERT INTO t1 VALUES(3, 6);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-1.$i.2 {
    sqlite3_wal db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-1.$i.3
  db close
  
  do_test walcrash-1.$i.4 {
    crashsql -delay 2 -file test.db-wal -seed [incr seed] {
      PRAGMA journal_mode = WAL;
      PRAGMA journal_mode = WAL;
      INSERT INTO t1 VALUES(4, (SELECT sum(a) FROM t1) + 4);
      INSERT INTO t1 VALUES(5, (SELECT sum(a) FROM t1) + 5);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-1.$i.5 {
    sqlite3_wal db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-1.$i.6



  db close
}

# walcrash-2.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
  file delete -force test.db test.db-wal
................................................................................
      CREATE TABLE t1(a PRIMARY KEY, b);
      INSERT INTO t1 VALUES(1, 2);
      INSERT INTO t1 VALUES(3, 4);
      INSERT INTO t1 VALUES(5, 9);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-2.$i.2 {
    sqlite3_wal db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-2.$i.3
  db close
  
  do_test walcrash-2.$i.4 {
    crashsql -delay 2 -file test.db-wal -seed [incr seed] {
      PRAGMA journal_mode = WAL;
      INSERT INTO t1 VALUES(6, (SELECT sum(a) FROM t1) + 6);
      INSERT INTO t1 VALUES(7, (SELECT sum(a) FROM t1) + 7);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-2.$i.5 {
    sqlite3_wal db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-2.$i.6



  db close
}

# walcrash-3.*
#
# for {set i 1} {$i < $REPEATS} {incr i} {
#   file delete -force test.db test.db-wal
................................................................................
      CREATE TABLE t1(a PRIMARY KEY, b);
      INSERT INTO t1 VALUES(1, 2);
      INSERT INTO t1 VALUES(3, 4);
    }
  } {1 {child process exited abnormally}}

  do_test walcrash-4.$i.2 {
    sqlite3_wal db test.db
    execsql { 
      SELECT * FROM t1 WHERE a = 1;
    }
  } {1 2}
  do_test walcrash-4.$i.3 { execsql { PRAGMA main.integrity_check } } {ok}


  db close
}

# walcrash-5.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
................................................................................
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
    }
  } {1 {child process exited abnormally}}

  do_test walcrash-5.$i.2 {
    sqlite3_wal db test.db
    execsql { SELECT count(*)==33 OR count(*)==34 FROM t1 WHERE x != 1 }
  } {1}
  do_test walcrash-5.$i.3 { execsql { PRAGMA main.integrity_check } } {ok}


  db close
}

# walcrash-6.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
................................................................................
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
    }
  } {1 {child process exited abnormally}}

  do_test walcrash-6.$i.2 {
    sqlite3_wal db test.db
    execsql { SELECT count(*)==34 OR count(*)==35 FROM t1 WHERE x != 1 }
  } {1}
  do_test walcrash-6.$i.3 { execsql { PRAGMA main.integrity_check } } {ok}




























  db close
}

finish_test

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

set seed 0
set REPEATS 100






# walcrash-1.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
  file delete -force test.db test.db-wal
  do_test walcrash-1.$i.1 {
    crashsql -delay 4 -file test.db-wal -seed [incr seed] {
      PRAGMA journal_mode = WAL;
................................................................................
      CREATE TABLE t1(a, b);
      INSERT INTO t1 VALUES(1, 1);
      INSERT INTO t1 VALUES(2, 3);
      INSERT INTO t1 VALUES(3, 6);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-1.$i.2 {
    sqlite3 db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-1.$i.3
  db close
  
  do_test walcrash-1.$i.4 {
    crashsql -delay 2 -file test.db-wal -seed [incr seed] {


      INSERT INTO t1 VALUES(4, (SELECT sum(a) FROM t1) + 4);
      INSERT INTO t1 VALUES(5, (SELECT sum(a) FROM t1) + 5);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-1.$i.5 {
    sqlite3 db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-1.$i.6
  do_test walcrash-1.$i.5 {
    execsql { PRAGMA main.journal_mode }
  } {wal}
  db close
}

# walcrash-2.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
  file delete -force test.db test.db-wal
................................................................................
      CREATE TABLE t1(a PRIMARY KEY, b);
      INSERT INTO t1 VALUES(1, 2);
      INSERT INTO t1 VALUES(3, 4);
      INSERT INTO t1 VALUES(5, 9);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-2.$i.2 {
    sqlite3 db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-2.$i.3
  db close
  
  do_test walcrash-2.$i.4 {
    crashsql -delay 2 -file test.db-wal -seed [incr seed] {

      INSERT INTO t1 VALUES(6, (SELECT sum(a) FROM t1) + 6);
      INSERT INTO t1 VALUES(7, (SELECT sum(a) FROM t1) + 7);
    }
  } {1 {child process exited abnormally}}
  do_test walcrash-2.$i.5 {
    sqlite3 db test.db
    execsql { SELECT sum(a)==max(b) FROM t1 }
  } {1}
  integrity_check walcrash-2.$i.6
  do_test walcrash-2.$i.6 {
    execsql { PRAGMA main.journal_mode }
  } {wal}
  db close
}

# walcrash-3.*
#
# for {set i 1} {$i < $REPEATS} {incr i} {
#   file delete -force test.db test.db-wal
................................................................................
      CREATE TABLE t1(a PRIMARY KEY, b);
      INSERT INTO t1 VALUES(1, 2);
      INSERT INTO t1 VALUES(3, 4);
    }
  } {1 {child process exited abnormally}}

  do_test walcrash-4.$i.2 {
    sqlite3 db test.db
    execsql { 
      SELECT * FROM t1 WHERE a = 1;
    }
  } {1 2}
  do_test walcrash-4.$i.3 { execsql { PRAGMA main.integrity_check } } {ok}
  do_test walcrash-4.$i.4 { execsql { PRAGMA main.journal_mode } } {wal}

  db close
}

# walcrash-5.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
................................................................................
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
    }
  } {1 {child process exited abnormally}}

  do_test walcrash-5.$i.2 {
    sqlite3 db test.db
    execsql { SELECT count(*)==33 OR count(*)==34 FROM t1 WHERE x != 1 }
  } {1}
  do_test walcrash-5.$i.3 { execsql { PRAGMA main.integrity_check } } {ok}
  do_test walcrash-5.$i.4 { execsql { PRAGMA main.journal_mode } } {wal}

  db close
}

# walcrash-6.*
#
for {set i 1} {$i < $REPEATS} {incr i} {
................................................................................
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
      INSERT INTO t1 VALUES(randomblob(900));
    }
  } {1 {child process exited abnormally}}

  do_test walcrash-6.$i.2 {
    sqlite3 db test.db
    execsql { SELECT count(*)==34 OR count(*)==35 FROM t1 WHERE x != 1 }
  } {1}
  do_test walcrash-6.$i.3 { execsql { PRAGMA main.integrity_check } } {ok}
  do_test walcrash-6.$i.4 { execsql { PRAGMA main.journal_mode } } {wal}

  db close
}

for {set i 1} {$i < $REPEATS} {incr i} {
  file delete -force test.db test.db-wal

  do_test walcrash-7.$i.1 {
    crashsql -delay 3 -file test.db -seed [incr seed] -blocksize 512 {
      PRAGMA journal_mode = wal;
      BEGIN;
        CREATE TABLE t1(a, b);
        INSERT INTO t1 VALUES(1, 2);
      COMMIT;
      PRAGMA checkpoint;
      CREATE INDEX i1 ON t1(a);
      PRAGMA checkpoint;
    }
  } {1 {child process exited abnormally}}

  do_test walcrash-7.$i.2 {
    sqlite3 db test.db
    execsql { SELECT b FROM t1 WHERE a = 1 }
  } {2}
  do_test walcrash-7.$i.3 { execsql { PRAGMA main.integrity_check } } {ok}
  do_test walcrash-7.$i.4 { execsql { PRAGMA main.journal_mode } } {wal}

  db close
}

finish_test