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 1.576 2009/03/31 02:54:40 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"

/*
** Macros for troubleshooting.  Normally turned off
*/

  ** the page is marked as needSync==0.
  **
  ** 2008-04-14:  When attempting to vacuum a corrupt database file, it
  ** is possible to fail a statement on a database that does not yet exist.
  ** Do not attempt to write if database file has never been opened.
  */
  pPg = pager_lookup(pPager, pgno);
  assert( pPg || !MEMDB );
  PAGERTRACE(("PLAYBACK %d page %d hash(%08x) %s\n",
               PAGERID(pPager), pgno, pager_datahash(pPager->pageSize, aData),
               (isMainJrnl?"main-journal":"sub-journal")
  ));
  if( (pPager->state>=PAGER_EXCLUSIVE)
   && (pPg==0 || 0==(pPg->flags&PGHDR_NEED_SYNC))
   && isOpen(pPager->fd)

** This function may return SQLITE_NOMEM or an IO error code if an error
** occurs. Otherwise, it returns SQLITE_OK.
*/
int sqlite3PagerMovepage(Pager *pPager, DbPage *pPg, Pgno pgno, int isCommit){
  PgHdr *pPgOld;               /* The page being overwritten. */
  Pgno needSyncPgno = 0;       /* Old value of pPg->pgno, if sync is required */
  int rc;                      /* Return code */
  Pgno origPgno;               /* The original page number */

  assert( pPg->nRef>0 );

  /* If the page being moved is dirty and has not been saved by the latest
  ** savepoint, then save the current contents of the page into the 
  ** sub-journal now. This is required to handle the following scenario:
  **

  pPg->flags &= ~PGHDR_NEED_SYNC;
  pPgOld = pager_lookup(pPager, pgno);
  assert( !pPgOld || pPgOld->nRef==1 );
  if( pPgOld ){
    pPg->flags |= (pPgOld->flags&PGHDR_NEED_SYNC);
  }

  origPgno = pPg->pgno;
  sqlite3PcacheMove(pPg, pgno);
  if( pPgOld ){
    sqlite3PcacheDrop(pPgOld);
  }

  sqlite3PcacheMakeDirty(pPg);
  pPager->dbModified = 1;

    }
    pPager->needSync = 1;
    assert( pPager->noSync==0 && !MEMDB );
    pPgHdr->flags |= PGHDR_NEED_SYNC;
    sqlite3PcacheMakeDirty(pPgHdr);
    sqlite3PagerUnref(pPgHdr);
  }

  /*
  ** For an in-memory database, make sure the original page continues
  ** to exist, in case the transaction needs to roll back.  We allocate
  ** the page now, instead of at rollback, because we can better deal
  ** with an out-of-memory error now.  Ticket #3761.
  */
  if( MEMDB ){
    DbPage *pNew;
    rc = sqlite3PagerAcquire(pPager, origPgno, &pNew, 1);
    if( rc!=SQLITE_OK ) return rc;
    sqlite3PagerUnref(pNew);
  }

  return SQLITE_OK;
}
#endif

/*
** Return a pointer to the data for the specified page.

# 2009 March 30
#
# 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.
#
#***********************************************************************
#
# Ticket #3761:  Make sure that an incremental vacuum on an in-memory
# database can be rolled back.
#
# $Id: tkt3761.test,v 1.1 2009/03/31 02:54:40 drh Exp $

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

do_test tkt3761-1.1 {
  db close
  sqlite3 db :memory:
  db eval {
    PRAGMA auto_vacuum=INCREMENTAL;
    CREATE TABLE t1(x);
    INSERT INTO t1 VALUES(zeroblob(900));
    INSERT INTO t1 VALUES(zeroblob(900));
    INSERT INTO t1 SELECT x FROM t1;
    INSERT INTO t1 SELECT x FROM t1;
    INSERT INTO t1 SELECT x FROM t1;
    INSERT INTO t1 SELECT x FROM t1;
    BEGIN;
    DELETE FROM t1 WHERE rowid%2;
    PRAGMA incremental_vacuum(4);
    ROLLBACK;
  }
  db eval {PRAGMA integrity_check}
} {ok}

finish_test