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 1.546 2009/01/10 17:02:03 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"

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

  u8 fullSync;                /* Do extra syncs of the journal for robustness */
  u8 sync_flags;              /* One of SYNC_NORMAL or SYNC_FULL */
  u8 state;                   /* PAGER_UNLOCK, _SHARED, _RESERVED, etc. */
  u8 tempFile;                /* zFilename is a temporary file */
  u8 readOnly;                /* True for a read-only database */
  u8 needSync;                /* True if an fsync() is needed on the journal */
  u8 dirtyCache;              /* True if cached pages have changed */
  u8 alwaysRollback;          /* Disable DontRollback() for all pages */
  u8 memDb;                   /* True to inhibit all file I/O */
  u8 setMaster;               /* True if a m-j name has been written to jrnl */
  u8 doNotSync;               /* Boolean. While true, do not spill the cache */
  u8 exclusiveMode;           /* Boolean. True if locking_mode==EXCLUSIVE */
  u8 journalMode;             /* On of the PAGER_JOURNALMODE_* values */
  u8 dbModified;              /* True if there are any changes to the Db */
  u8 changeCountDone;         /* Set after incrementing the change-counter */

** on the given page is unused.  The pager marks the page as clean so
** that it does not get written to disk.
**
** Tests show that this optimization, together with the
** sqlite3PagerDontRollback() below, more than double the speed
** of large INSERT operations and quadruple the speed of large DELETEs.
**
** When this routine is called, set the alwaysRollback flag to true.

** Subsequent calls to sqlite3PagerDontRollback() for the same page
** will thereafter be ignored.  This is necessary to avoid a problem
** where a page with data is added to the freelist during one part of
** a transaction then removed from the freelist during a later part
** of the same transaction and reused for some other purpose.  When it
** is first added to the freelist, this routine is called.  When reused,
** the sqlite3PagerDontRollback() routine is called.  But because the
** page contains critical data, we still need to be sure it gets
** rolled back in spite of the sqlite3PagerDontRollback() call.
*/
int sqlite3PagerDontWrite(DbPage *pDbPage){
  PgHdr *pPg = pDbPage;
  Pager *pPager = pPg->pPager;
  int rc;

  if( pPg->pgno>pPager->dbOrigSize ){

void sqlite3PagerDontRollback(DbPage *pPg){
  Pager *pPager = pPg->pPager;
  TESTONLY( int rc; )  /* Return value from sqlite3BitvecSet() */

  assert( pPager->state>=PAGER_RESERVED );

  /* If the journal file is not open, or DontWrite() has been called on
  ** this page (DontWrite() sets the alwaysRollback flag), then this
  ** function is a no-op.
  */
  if( pPager->journalOpen==0 
   || sqlite3BitvecTest(pPager->pAlwaysRollback, pPg->pgno)
   || pPg->pgno>pPager->dbOrigSize
  ){
    return;