*/
  pBt->doNotUseWAL = (iVersion==1);

  rc = sqlite3BtreeBeginTrans(pBtree, 0);
  if( rc==SQLITE_OK ){
    u8 *aData = pBt->pPage1->aData;
    if( aData[18]!=(u8)iVersion || aData[19]!=(u8)iVersion ){
      rc = sqlite3BtreeBeginTrans(pBtree, 1);
      if( rc==SQLITE_OK ){
        rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
        if( rc==SQLITE_OK ){
          aData[18] = (u8)iVersion;
          aData[19] = (u8)iVersion;
        }
      }
    }
  }

  pBt->doNotUseWAL = 0;
  return rc;
}

  */
  pBt->doNotUseWAL = (iVersion==1);

  rc = sqlite3BtreeBeginTrans(pBtree, 0);
  if( rc==SQLITE_OK ){
    u8 *aData = pBt->pPage1->aData;
    if( aData[18]!=(u8)iVersion || aData[19]!=(u8)iVersion ){
      rc = sqlite3BtreeBeginTrans(pBtree, 2);
      if( rc==SQLITE_OK ){
        rc = sqlite3PagerWrite(pBt->pPage1->pDbPage);
        if( rc==SQLITE_OK ){
          aData[18] = (u8)iVersion;
          aData[19] = (u8)iVersion;
        }
      }
    }
  }

  pBt->doNotUseWAL = 0;
  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( pPager->state>=PAGER_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);
................................................................................
** Before closing the log file, this function attempts to take an 
** EXCLUSIVE lock on the database file. If this cannot be obtained, an
** error (SQLITE_BUSY) is returned and the log connection is not closed.
** If successful, the EXCLUSIVE lock is not released before returning.
*/
int sqlite3PagerCloseLog(Pager *pPager){
  int rc = SQLITE_OK;
  if( pPager->pLog ){

    /* Try to obtain an EXCLUSIVE lock on the database file. */








    rc = sqlite3OsLock(pPager->fd, SQLITE_LOCK_EXCLUSIVE);








    /* If the EXCLUSIVE lock was obtained, checkpoint and close the log. */




    if( rc==SQLITE_OK ){
      rc = sqlite3LogClose(pPager->pLog, pPager->fd,
        (pPager->noSync ? 0 : pPager->sync_flags), 
        (u8*)pPager->pTmpSpace
      );
      pPager->pLog = 0;
    }
  }
  return rc;
}

#endif /* SQLITE_OMIT_DISKIO */

/*
** 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. 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.
*/
static int pagerHasWAL(Pager *pPager, int *pExists){
  int rc;                         /* Return code */








  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);
................................................................................
** Before closing the log file, this function attempts to take an 
** EXCLUSIVE lock on the database file. If this cannot be obtained, an
** error (SQLITE_BUSY) is returned and the log connection is not closed.
** If successful, the EXCLUSIVE lock is not released before returning.
*/
int sqlite3PagerCloseLog(Pager *pPager){
  int rc = SQLITE_OK;



  assert( pPager->journalMode==PAGER_JOURNALMODE_WAL );

  /* If the log file is not already open, but does exist in the file-system,
  ** it may need to be checkpointed before the connection can switch to
  ** rollback mode. Open it now so this can happen.
  */
  if( !pPager->pLog ){
    int logexists = 0;
    rc = sqlite3OsLock(pPager->fd, SQLITE_LOCK_SHARED);
    if( rc==SQLITE_OK ){
      rc = pagerHasWAL(pPager, &logexists);
    }
    if( rc==SQLITE_OK && logexists ){
      rc = sqlite3LogOpen(pPager->pVfs, pPager->zFilename, &pPager->pLog);
    }
  }
    
  /* Checkpoint and close the log. Because an EXCLUSIVE lock is held on
  ** the database file, the log and log-summary files will be deleted.
  */
  if( rc==SQLITE_OK && pPager->pLog ){
    rc = sqlite3OsLock(pPager->fd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      rc = sqlite3LogClose(pPager->pLog, pPager->fd,
        (pPager->noSync ? 0 : pPager->sync_flags), 
        (u8*)pPager->pTmpSpace
      );
      pPager->pLog = 0;
    }
  }
  return rc;
}

#endif /* SQLITE_OMIT_DISKIO */

        rc = SQLITE_ERROR;
        sqlite3SetString(&p->zErrMsg, db, 
            "cannot change %s wal mode from within a transaction",
            (eNew==PAGER_JOURNALMODE_WAL ? "into" : "out of")
        );
      }else{
  

        /* If leaving WAL mode, close the log file. If successful, the call to
        ** PagerCloseLog() checkpoints and deletes the write-ahead-log file.
        ** An EXCLUSIVE lock is still held on the database file after returning.

        */
        if( eOld==PAGER_JOURNALMODE_WAL ){
          rc = sqlite3PagerCloseLog(pPager);
          if( rc!=SQLITE_OK ) goto abort_due_to_error;
          sqlite3PagerJournalMode(pPager, eNew);
        }else{
          sqlite3PagerJournalMode(pPager, PAGER_JOURNALMODE_DELETE);
        }
  

        rc = SQLITE_ERROR;
        sqlite3SetString(&p->zErrMsg, db, 
            "cannot change %s wal mode from within a transaction",
            (eNew==PAGER_JOURNALMODE_WAL ? "into" : "out of")
        );
      }else{
  
        if( eOld==PAGER_JOURNALMODE_WAL ){
          /* If leaving WAL mode, close the log file. If successful, the call
          ** to PagerCloseLog() checkpoints and deletes the write-ahead-log 
          ** file. An EXCLUSIVE lock may still be held on the database file 
          ** after a successful return. 
          */

          rc = sqlite3PagerCloseLog(pPager);
          if( rc!=SQLITE_OK ) goto abort_due_to_error;
          sqlite3PagerJournalMode(pPager, eNew);
        }else{
          sqlite3PagerJournalMode(pPager, PAGER_JOURNALMODE_DELETE);
        }
  

  sqlite3 db test.db
  execsql { PRAGMA journal_mode = wal }
} {wal}
do_test walmode-3.2 {
  list $sqlite_sync_count [file exists test.db-wal] [file size test.db-wal]
} {0 1 0}



do_test walmode-4.1 {
  execsql { INSERT INTO t1 VALUES(1, 2) }
  execsql { PRAGMA journal_mode = persist }
} {persist}
do_test walmode-4.2 {
  list [file exists test.db-journal] [file exists test.db-wal]
} {1 0}
................................................................................
  sqlite3 db test.db
  execsql { SELECT * FROM t1 }
} {1 2}
do_test walmode-4.5 {
  list [file exists test.db-journal] [file exists test.db-wal]
} {1 0}



















































finish_test

  sqlite3 db test.db
  execsql { PRAGMA journal_mode = wal }
} {wal}
do_test walmode-3.2 {
  list $sqlite_sync_count [file exists test.db-wal] [file size test.db-wal]
} {0 1 0}

# Test that changing back to journal_mode=persist works.
#
do_test walmode-4.1 {
  execsql { INSERT INTO t1 VALUES(1, 2) }
  execsql { PRAGMA journal_mode = persist }
} {persist}
do_test walmode-4.2 {
  list [file exists test.db-journal] [file exists test.db-wal]
} {1 0}
................................................................................
  sqlite3 db test.db
  execsql { SELECT * FROM t1 }
} {1 2}
do_test walmode-4.5 {
  list [file exists test.db-journal] [file exists test.db-wal]
} {1 0}

# Test that nothing goes wrong if a connection is prevented from changing
# from WAL to rollback mode because a second connection has the database
# open. Or from rollback to WAL.
#
do_test walmode-4.1 {
  sqlite3 db2 test.db
  execsql { PRAGMA main.journal_mode } db2
} {delete}
do_test walmode-4.2 {
  execsql { PRAGMA main.journal_mode = wal } db
} {wal}
do_test walmode-4.3 {
  execsql { SELECT * FROM t1 } db2
} {1 2}
do_test walmode-4.4 {
  catchsql { PRAGMA journal_mode = delete } db
} {1 {database is locked}}
do_test walmode-4.5 {
  execsql { PRAGMA main.journal_mode } db
} {wal}
do_test walmode-4.6 {
  db2 close
  execsql { PRAGMA journal_mode = delete } db
} {delete}
do_test walmode-4.7 {
  execsql { PRAGMA main.journal_mode } db
} {delete}
do_test walmode-4.8 {
  list [file exists test.db-journal] [file exists test.db-wal]
} {0 0}
do_test walmode-4.9 {
  sqlite3 db2 test.db
  execsql {
    BEGIN;
      SELECT * FROM t1;
  } db2
} {1 2}
do_test walmode-4.11 {
  execsql { PRAGMA main.journal_mode } db
} {delete}
do_test walmode-4.10 {
  catchsql { PRAGMA main.journal_mode = wal } db
} {1 {database is locked}}
do_test walmode-4.11 {
  execsql { PRAGMA main.journal_mode } db
} {delete}


catch { db close }
catch { db2 close }
finish_test