** 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 1.64 2003/01/03 02:04:27 drh Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
  char *zJournal;             /* Name of the journal file */
  OsFile fd, jfd;             /* File descriptors for database and journal */
  OsFile cpfd;                /* File descriptor for the checkpoint journal */
  int dbSize;                 /* Number of pages in the file */
  int origDbSize;             /* dbSize before the current change */
  int ckptSize;               /* Size of database (in pages) at ckpt_begin() */
  off_t ckptJSize;            /* Size of journal at ckpt_begin() */

  int nExtra;                 /* Add this many bytes to each in-memory page */
  void (*xDestructor)(void*); /* Call this routine when freeing pages */
  int nPage;                  /* Total number of in-memory pages */
  int nRef;                   /* Number of in-memory pages with PgHdr.nRef>0 */
  int mxPage;                 /* Maximum number of pages to hold in cache */
  int nHit, nMiss, nOvfl;     /* Cache hits, missing, and LRU overflows */
  u8 journalOpen;             /* True if journal file descriptors is valid */
................................................................................
  rc = sqliteOsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)pPager->ckptSize);
  pPager->dbSize = pPager->ckptSize;

  /* Figure out how many records are in the checkpoint journal.
  */
  assert( pPager->ckptInUse && pPager->journalOpen );
  sqliteOsSeek(&pPager->cpfd, 0);
  rc = sqliteOsFileSize(&pPager->cpfd, &nRec);
  if( rc!=SQLITE_OK ){
    goto end_ckpt_playback;
  }
  nRec /= sizeof(PageRecord);
  
  /* Copy original pages out of the checkpoint journal and back into the
  ** database file.
  */
  if( pager_old_format ){
    pPager->journalFormat = SQLITE_OLD_JOURNAL_FORMAT;
  }else{
................................................................................
      rc = sqliteOsWrite(&pPager->cpfd, pData, SQLITE_PAGE_SIZE);
    }
    if( rc!=SQLITE_OK ){
      sqlitepager_rollback(pPager);
      pPager->errMask |= PAGER_ERR_FULL;
      return rc;
    }

    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_ckpt_list(pPg);
  }

  /* Update the database size and return.
  */
................................................................................
  rc = sqliteOsFileSize(&pPager->jfd, &pPager->ckptJSize);
  if( rc ) goto ckpt_begin_failed;
  pPager->ckptSize = pPager->dbSize;
  if( !pPager->ckptOpen ){
    rc = sqlitepager_opentemp(zTemp, &pPager->cpfd);
    if( rc ) goto ckpt_begin_failed;
    pPager->ckptOpen = 1;

  }
  pPager->ckptInUse = 1;
  return SQLITE_OK;
 
ckpt_begin_failed:
  if( pPager->aInCkpt ){
    sqliteFree(pPager->aInCkpt);
................................................................................
/*
** Commit a checkpoint.
*/
int sqlitepager_ckpt_commit(Pager *pPager){
  if( pPager->ckptInUse ){
    PgHdr *pPg, *pNext;
    sqliteOsSeek(&pPager->cpfd, 0);
    sqliteOsTruncate(&pPager->cpfd, 0);

    pPager->ckptInUse = 0;
    sqliteFree( pPager->aInCkpt );
    pPager->aInCkpt = 0;
    for(pPg=pPager->pCkpt; pPg; pPg=pNext){
      pNext = pPg->pNextCkpt;
      assert( pPg->inCkpt );
      pPg->inCkpt = 0;

** 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 1.65 2003/01/07 14:46:08 drh Exp $
*/
#include "os.h"         /* Must be first to enable large file support */
#include "sqliteInt.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

................................................................................
  char *zJournal;             /* Name of the journal file */
  OsFile fd, jfd;             /* File descriptors for database and journal */
  OsFile cpfd;                /* File descriptor for the checkpoint journal */
  int dbSize;                 /* Number of pages in the file */
  int origDbSize;             /* dbSize before the current change */
  int ckptSize;               /* Size of database (in pages) at ckpt_begin() */
  off_t ckptJSize;            /* Size of journal at ckpt_begin() */
  int ckptNRec;               /* Number of records in the checkpoint journal */
  int nExtra;                 /* Add this many bytes to each in-memory page */
  void (*xDestructor)(void*); /* Call this routine when freeing pages */
  int nPage;                  /* Total number of in-memory pages */
  int nRef;                   /* Number of in-memory pages with PgHdr.nRef>0 */
  int mxPage;                 /* Maximum number of pages to hold in cache */
  int nHit, nMiss, nOvfl;     /* Cache hits, missing, and LRU overflows */
  u8 journalOpen;             /* True if journal file descriptors is valid */
................................................................................
  rc = sqliteOsTruncate(&pPager->fd, SQLITE_PAGE_SIZE*(off_t)pPager->ckptSize);
  pPager->dbSize = pPager->ckptSize;

  /* Figure out how many records are in the checkpoint journal.
  */
  assert( pPager->ckptInUse && pPager->journalOpen );
  sqliteOsSeek(&pPager->cpfd, 0);
  nRec = pPager->ckptNRec;




  
  /* Copy original pages out of the checkpoint journal and back into the
  ** database file.
  */
  if( pager_old_format ){
    pPager->journalFormat = SQLITE_OLD_JOURNAL_FORMAT;
  }else{
................................................................................
      rc = sqliteOsWrite(&pPager->cpfd, pData, SQLITE_PAGE_SIZE);
    }
    if( rc!=SQLITE_OK ){
      sqlitepager_rollback(pPager);
      pPager->errMask |= PAGER_ERR_FULL;
      return rc;
    }
    pPager->ckptNRec++;
    assert( pPager->aInCkpt!=0 );
    pPager->aInCkpt[pPg->pgno/8] |= 1<<(pPg->pgno&7);
    page_add_to_ckpt_list(pPg);
  }

  /* Update the database size and return.
  */
................................................................................
  rc = sqliteOsFileSize(&pPager->jfd, &pPager->ckptJSize);
  if( rc ) goto ckpt_begin_failed;
  pPager->ckptSize = pPager->dbSize;
  if( !pPager->ckptOpen ){
    rc = sqlitepager_opentemp(zTemp, &pPager->cpfd);
    if( rc ) goto ckpt_begin_failed;
    pPager->ckptOpen = 1;
    pPager->ckptNRec = 0;
  }
  pPager->ckptInUse = 1;
  return SQLITE_OK;
 
ckpt_begin_failed:
  if( pPager->aInCkpt ){
    sqliteFree(pPager->aInCkpt);
................................................................................
/*
** Commit a checkpoint.
*/
int sqlitepager_ckpt_commit(Pager *pPager){
  if( pPager->ckptInUse ){
    PgHdr *pPg, *pNext;
    sqliteOsSeek(&pPager->cpfd, 0);
    /* sqliteOsTruncate(&pPager->cpfd, 0); */
    pPager->ckptNRec = 0;
    pPager->ckptInUse = 0;
    sqliteFree( pPager->aInCkpt );
    pPager->aInCkpt = 0;
    for(pPg=pPager->pCkpt; pPg; pPg=pNext){
      pNext = pPg->pNextCkpt;
      assert( pPg->inCkpt );
      pPg->inCkpt = 0;