SQLite

** The pager is used to access a database disk file.  It implements
** atomic commit and rollback through the use of a journal file that
** is separate from the database file.  The pager also implements file
** locking to prevent two processes from writing the same database
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.194 2005/03/15 17:09:30 drh Exp $
*/
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

    if( p->dirty ){
      p->pDirty = pList;
      pList = p;
    }
  }
  return pList;
}

/*
** Return TRUE if there is a hot journal on the given pager.
** A hot journal is one that needs to be played back.
**
** If the current size of the database file is 0 but a journal file
** exists, that is probably an old journal left over from a prior
** database with the same name.  Just delete the journal.
*/
static int hasHotJournal(Pager *pPager){
  if( !pPager->useJournal ) return 0;
  if( !sqlite3OsFileExists(pPager->zJournal) ) return 0;
  if( sqlite3OsCheckReservedLock(&pPager->fd) ) return 0;
  if( sqlite3pager_pagecount(pPager)==0 ){
    sqlite3OsDelete(pPager->zJournal);
    return 0;
  }else{
    return 1;
  }
}

/*
** Acquire a page.
**
** A read lock on the disk file is obtained when the first page is acquired. 
** This read lock is dropped when the last page is released.
**

** just returns 0.  This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since _lookup() never goes to disk, it never has to deal with locks
** or journal files.
*/
int sqlite3pager_get(Pager *pPager, Pgno pgno, void **ppPage){
  PgHdr *pPg;
  int rc;

  /* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
  ** number greater than this, or zero, is requested.
  */
  if( pgno>PAGER_MAX_PGNO || pgno==0 ){
    return SQLITE_CORRUPT;
  }

        return rc;
      }
    }

    /* If a journal file exists, and there is no RESERVED lock on the
    ** database file, then it either needs to be played back or deleted.
    */
    if( hasHotJournal(pPager) ){



       int rc;

       /* Get an EXCLUSIVE lock on the database file. At this point it is
       ** important that a RESERVED lock is not obtained on the way to the
       ** EXCLUSIVE lock. If it were, another process might open the
       ** database file, detect the RESERVED lock, and conclude that the
       ** database is safe to read while this process is still rolling it 

    if( pPg->pNextHash ){
      assert( pPg->pNextHash->pPrevHash==0 );
      pPg->pNextHash->pPrevHash = pPg;
    }
    if( pPager->nExtra>0 ){
      memset(PGHDR_TO_EXTRA(pPg, pPager), 0, pPager->nExtra);
    }

    if( pPager->errMask!=0 ){
      sqlite3pager_unref(PGHDR_TO_DATA(pPg));
      rc = pager_errcode(pPager);
      return rc;
    }
    if( sqlite3pager_pagecount(pPager)<(int)pgno ){
      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
    }else{
      int rc;
      assert( MEMDB==0 );
      sqlite3OsSeek(&pPager->fd, (pgno-1)*(i64)pPager->pageSize);
      rc = sqlite3OsRead(&pPager->fd, PGHDR_TO_DATA(pPg), pPager->pageSize);
      TRACE3("FETCH %d page %d\n", PAGERID(pPager), pPg->pgno);

# 2005 March 15
#
# 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 file implements regression tests for SQLite library.
#
# This file implements tests to make sure that leftover journals from
# prior databases do not try to rollback into new databases.
#
# $Id: journal1.test,v 1.1 2005/03/15 17:09:30 drh Exp $


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

# Create a smaple database
#
do_test journal1-1.1 {
  execsql {
    CREATE TABLE t1(a,b);
    INSERT INTO t1 VALUES(1,randstr(10,400));
    INSERT INTO t1 VALUES(2,randstr(10,400));
    INSERT INTO t1 SELECT a+2, a||b FROM t1;
    INSERT INTO t1 SELECT a+4, a||b FROM t1;
    SELECT count(*) FROM t1;
  }
} 8

# Make changes to the database and save the journal file.
# Then delete the database.  Replace the the journal file
# and try to create a new database with the same name.  The
# old journal should not attempt to rollback into the new
# database.
#
do_test journal1-1.2 {
  execsql {
    BEGIN;
    DELETE FROM t1;
  }
  file copy -force test.db-journal test.db-journal-bu
  execsql {
    ROLLBACK;
  }
  db close
  file delete test.db
  file copy test.db-journal-bu test.db-journal
  sqlite3 db test.db
  catchsql {
    SELECT * FROM sqlite_master
  }
} {0 {}}

finish_test