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 1.323 2007/04/05 17:15:53 danielk1977 Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
#include "os.h"
#include "pager.h"
#include <assert.h>
#include <string.h>

  pager_unlock(p);
  assert( p->errCode || !p->journalOpen || (p->exclusiveMode&&!p->journalOff) );
  assert( p->errCode || !p->stmtOpen || p->exclusiveMode );
}


/*
** Clear the in-memory cache.  This routine
** sets the state of the pager back to what it was when it was first
** opened.  Any outstanding pages are invalidated and subsequent attempts
** to access those pages will likely result in a coredump.
*/
static void pager_reset(Pager *pPager){
  PgHdr *pPg, *pNext;
  if( pPager->errCode ) return;

#endif
  }
  pPager->pDirty = 0;
  return rc;
}
#endif

static void pager_truncate_cache(Pager *pPager);

/*
** Truncate the main file of the given pager to the number of pages
** indicated. Also truncate the cached representation of the file.
*/
static int pager_truncate(Pager *pPager, int nPage){
  int rc = SQLITE_OK;
  if( pPager->state>=PAGER_EXCLUSIVE ){
    rc = sqlite3OsTruncate(pPager->fd, pPager->pageSize*(i64)nPage);
  }
  if( rc==SQLITE_OK ){
    pPager->dbSize = nPage;
    pager_truncate_cache(pPager);
  }
  return rc;
}

/*
** Playback the journal and thus restore the database file to
** the state it was in before we started making changes.  
**
** The journal file format is as follows: 

    if( nRec==0 && !isHot ){
      nRec = (szJ - pPager->journalOff) / JOURNAL_PG_SZ(pPager);
    }

    /* If this is the first header read from the journal, truncate the
    ** database file back to it's original size.
    */

    if( pPager->journalOff==JOURNAL_HDR_SZ(pPager) ){

      rc = pager_truncate(pPager, mxPg);
      if( rc!=SQLITE_OK ){
        goto end_playback;
      }

    }

    /* Copy original pages out of the journal and back into the database file.
    */
    for(i=0; i<nRec; i++){
      rc = pager_playback_one_page(pPager, pPager->jfd, 1);
      if( rc!=SQLITE_OK ){

  assert( pPager->fullSync || !hdrOff );
  if( !hdrOff ){
    hdrOff = szJ;
  }
  
  /* Truncate the database back to its original size.
  */

    rc = pager_truncate(pPager, pPager->stmtSize);

  assert( pPager->state>=PAGER_SHARED );


  /* Figure out how many records are in the statement journal.
  */
  assert( pPager->stmtInUse && pPager->journalOpen );
  sqlite3OsSeek(pPager->stfd, 0);
  nRec = pPager->stmtNRec;
  

  }
  pPg->pNextFree = pPg->pPrevFree = 0;

  /* Unlink from the pgno hash table */
  unlinkHashChain(pPager, pPg);
}


/*
** This routine is used to truncate the cache when a database
** is truncated.  Drop from the cache all pages whose pgno is
** larger than pPager->dbSize and is unreferenced.
**
** Referenced pages larger than pPager->dbSize are zeroed.
**
** Actually, at the point this routine is called, it would be
** an error to have a referenced page.  But rather than delete
** that page and guarantee a subsequent segfault, it seems better
** to zero it and hope that we error out sanely.
*/
static void pager_truncate_cache(Pager *pPager){
  PgHdr *pPg;
  PgHdr **ppPg;
  int dbSize = pPager->dbSize;

  ppPg = &pPager->pAll;
  while( (pPg = *ppPg)!=0 ){
    if( pPg->pgno<=dbSize ){
      ppPg = &pPg->pNextAll;
    }else if( pPg->nRef>0 ){
      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
      ppPg = &pPg->pNextAll;
    }else{
      *ppPg = pPg->pNextAll;
      unlinkPage(pPg);
      makeClean(pPg);
      sqliteFree(pPg);
      pPager->nPage--;
    }
  }
}




/*
** Try to obtain a lock on a file.  Invoke the busy callback if the lock
** is currently not available.  Repeat until the busy callback returns
** false or until the lock succeeds.
**
** Return SQLITE_OK on success and an error code if we cannot obtain

    return rc;
  }
  if( nPage>=(unsigned)pPager->dbSize ){
    return SQLITE_OK;
  }
  if( MEMDB ){
    pPager->dbSize = nPage;
    pager_truncate_cache(pPager);
    return SQLITE_OK;
  }
  rc = syncJournal(pPager);
  if( rc!=SQLITE_OK ){
    return rc;
  }

  /* Get an exclusive lock on the database before truncating. */
  rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
  if( rc!=SQLITE_OK ){
    return rc;
  }

  rc = pager_truncate(pPager, nPage);



  return rc;
}

/*
** Shutdown the page cache.  Free all memory and close all files.
**
** If a transaction was in progress when this routine is called, that

      }
    }
  }

  return nReleased;
}
#endif /* SQLITE_ENABLE_MEMORY_MANAGEMENT */

/*
** Read the content of page pPg out of the database file.
*/
static int readDbPage(Pager *pPager, PgHdr *pPg, Pgno pgno){
  int rc;
  assert( MEMDB==0 );
  rc = sqlite3OsSeek(pPager->fd, (pgno-1)*(i64)pPager->pageSize);
  if( rc==SQLITE_OK ){
    rc = sqlite3OsRead(pPager->fd, PGHDR_TO_DATA(pPg),
                          pPager->pageSize);
  }
  IOTRACE(("PGIN %p %d\n", pPager, pgno))
  PAGERTRACE3("FETCH %d page %d\n", PAGERID(pPager), pPg->pgno);
  CODEC1(pPager, PGHDR_TO_DATA(pPg), pPg->pgno, 3);
  return rc;
}


/*
** This function is called to obtain the shared lock required before
** data may be read from the pager cache. If the shared lock has already
** been obtained, this function is a no-op.
**
** Immediately after obtaining the shared lock (if required), this function

        ** stored in Pager.iChangeCount matches that found on page 1 of
        ** the database file, then no database changes have occured since
        ** the cache was last valid and it is safe to retain the cached
        ** pages. Otherwise, if Pager.iChangeCount does not match the
        ** change-counter on page 1 of the file, the current cache contents
        ** must be discarded.
        */
        u8 zC[4];
        u32 iChangeCounter = 0;
        sqlite3PagerPagecount(pPager);


        if( pPager->errCode ){
          return pPager->errCode;
        }







        if( pPager->dbSize>0 ){
          /* Read the 4-byte change counter directly from the file. */
          rc = sqlite3OsSeek(pPager->fd, 24);
          if( rc!=SQLITE_OK ){
            return rc;


          }
          rc = sqlite3OsRead(pPager->fd, zC, 4);

          if( rc!=SQLITE_OK ){
            return rc;
        }
          iChangeCounter = (zC[0]<<24) + (zC[1]<<16) + (zC[2]<<8) + zC[3];
        }










        if( iChangeCounter!=pPager->iChangeCount ){
            pager_reset(pPager);


        }
      }
    }
    assert( pPager->exclusiveMode || pPager->state<=PAGER_SHARED );
    if( pPager->state==PAGER_UNLOCK ){
      pPager->state = PAGER_SHARED;
    }
  }

  return rc;
}

/*
** Allocate a PgHdr object.   Either create a new one or reuse
** an existing one that is not otherwise in use.
**
** A new PgHdr structure is created if any of the following are
** true:
**
**     (1)  We have not exceeded our maximum allocated cache size
**          as set by the "PRAGMA cache_size" command.
**
**     (2)  There are no unused PgHdr objects available at this time.
**
**     (3)  This is an in-memory database.
**
**     (4)  There are no PgHdr objects that do not require a journal
**          file sync and a sync of the journal file is currently
**          prohibited.
**
** Otherwise, reuse an existing PgHdr.  In other words, reuse an
** existing PgHdr if all of the following are true:
**
**     (1)  We have reached or exceeded the maximum cache size
**          allowed by "PRAGMA cache_size".
**
**     (2)  There is a PgHdr available with PgHdr->nRef==0
**
**     (3)  We are not in an in-memory database
**
**     (4)  Either there is an available PgHdr that does not need
**          to be synced to disk or else disk syncing is currently
**          allowed.
*/
static int pagerAllocatePage(Pager *pPager, PgHdr **ppPg){
  int rc = SQLITE_OK;
  PgHdr *pPg;

  /* Create a new PgHdr if any of the four conditions defined 
  ** above is met: */
  if( pPager->nPage<pPager->mxPage
   || pPager->pFirst==0 
   || MEMDB
   || (pPager->pFirstSynced==0 && pPager->doNotSync)
  ){

    if( pPager->nPage>=pPager->nHash ){
      pager_resize_hash_table(pPager,
         pPager->nHash<256 ? 256 : pPager->nHash*2);
      if( pPager->nHash==0 ){
        rc = SQLITE_NOMEM;
        goto pager_allocate_out;
      }

    /* Populate the page with data, either by reading from the database
    ** file, or by setting the entire page to zero.
    */
    if( nMax<(int)pgno || MEMDB || (clrFlag && !pPager->alwaysRollback) ){
      memset(PGHDR_TO_DATA(pPg), 0, pPager->pageSize);
    }else{






      rc = readDbPage(pPager, pPg, pgno);


      if( rc!=SQLITE_OK && rc!=SQLITE_IOERR_SHORT_READ ){
        pPg->pgno = 0;
        sqlite3PagerUnref(pPg);
        return rc;
      }else{
        TEST_INCR(pPager->nRead);
      }

#ifdef SQLITE_CHECK_PAGES
    pPg->pageHash = pager_pagehash(pPg);
#endif
  }else{
    /* The requested page is in the page cache. */
    assert(pPager->nRef>0 || pgno==1);














    TEST_INCR(pPager->nHit);
    page_ref(pPg);
  }
  *ppPage = pPg;
  return SQLITE_OK;
}

      if( pPager->xReiniter ){
        pPager->xReiniter(p, pPager->pageSize);
      }
    }
    pPager->pDirty = 0;
    pPager->pStmt = 0;
    pPager->dbSize = pPager->origDbSize;
    pager_truncate_cache(pPager);
    pPager->stmtInUse = 0;
    pPager->state = PAGER_SHARED;
    return SQLITE_OK;
  }

  if( !pPager->dirtyCache || !pPager->journalOpen ){
    rc = pager_end_transaction(pPager);

    rc2 = pager_end_transaction(pPager);
    if( rc==SQLITE_OK ){
      rc = rc2;
    }
  }else{
    rc = pager_playback(pPager, 0);
  }
  /* pager_reset(pPager); */
  pPager->dbSize = -1;

  /* If an error occurs during a ROLLBACK, we can no longer trust the pager
  ** cache. So call pager_error() on the way out to make any error 
  ** persistent.
  */
  return pager_error(pPager, rc);

        if( pHist->pStmt ){
          memcpy(PGHDR_TO_DATA(pPg), pHist->pStmt, pPager->pageSize);
          sqliteFree(pHist->pStmt);
          pHist->pStmt = 0;
        }
      }
      pPager->dbSize = pPager->stmtSize;
      pager_truncate_cache(pPager);
      rc = SQLITE_OK;
    }else{
      rc = pager_stmt_playback(pPager);
    }
    sqlite3PagerStmtCommit(pPager);
  }else{
    rc = SQLITE_OK;

#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing for correct handling of disk full
# errors.
# 
# $Id: diskfull.test,v 1.6 2007/04/05 17:15:53 danielk1977 Exp $

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

set sqlite_io_error_persist 0
set sqlite_io_error_hit 0
set sqlite_io_error_pending 0

set sqlite_diskfull_pending 0
set sqlite_io_error_hit 0
integrity_check diskfull-1.6

proc do_diskfull_test {prefix sql} {
  set ::go 1
  set ::sql $sql
  set ::i 1
  while {$::go} {
    incr ::i
    do_test ${prefix}.$::i.1 {
      set ::sqlite_diskfull_pending $::i
      set ::sqlite_diskfull 0
      set r [catchsql $::sql]
      if {!$::sqlite_diskfull} {

# 2001 September 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.  The
# focus of this script is page cache subsystem.
#
# $Id: pager.test,v 1.28 2007/04/05 17:15:53 danielk1977 Exp $


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

if {[info commands pager_open]!=""} {
db close

  expr {$::g1!=0}
} {1}
do_test pager-2.12 {
  page_number $::g1
} {1}
do_test pager-2.13 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 0 state 1 err 0 hit 1 miss 1 ovfl 0}
do_test pager-2.14 {
  set v [catch {
    page_write $::g1 "Page-One"
  } msg]
  lappend v $msg
} {0 {}}
do_test pager-2.15 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 1 state 2 err 0 hit 1 miss 1 ovfl 0}
do_test pager-2.16 {
  page_read $::g1
} {Page-One}
do_test pager-2.17 {
  set v [catch {
    pager_commit $::p1
  } msg]
  lappend v $msg
} {0 {}}
do_test pager-2.20 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size -1 state 1 err 0 hit 2 miss 1 ovfl 0}
do_test pager-2.19 {
  pager_pagecount $::p1
} {1}
do_test pager-2.21 {
  pager_stats $::p1
} {ref 1 page 1 max 10 size 1 state 1 err 0 hit 2 miss 1 ovfl 0}
do_test pager-2.22 {
  page_unref $::g1
} {}
do_test pager-2.23 {
  pager_stats $::p1
} {ref 0 page 1 max 10 size -1 state 0 err 0 hit 2 miss 1 ovfl 0}
do_test pager-2.24 {
  set v [catch {
    page_get $::p1 1
  } ::g1]
  if {$v} {lappend v $::g1}
  set v
} {0}