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Overview
Comment:Do not create, open, or initialize the rollback journal until something actually needs to be written into the journal. That way, expensive filesystem operations are avoided if the transaction ends up being a no-op.
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SHA1: b78e58ae1570ab4d66a69db445a752c6456038a0
User & Date: drh 2010-03-19 15:48:14
Original Comment: Do create, open, or initialize the rollback journal until something actually needs to be written into the journal. That way, expensive filesystem operations are avoided if the transaction ends up being a no-op.
References
2010-06-17
13:22 Ticket [fc62af45] Executing "PRAGMA journal_mode" may delete journal file while it is in use. status still Open with 1 other change artifact: 068d606e user: drh
10:45 Ticket [fc62af45]: 1 change artifact: deedf461 user: dan
09:52 Ticket [fc62af45]: 4 changes artifact: c98b4147 user: dan
Context
2010-03-19
16:52
Make sure the in-journal boolean vector is cleared and released when ending a transaction. This fixes an obscure problem with the previous check-in. check-in: 69d749d9 user: drh tags: trunk
15:48
Do not create, open, or initialize the rollback journal until something actually needs to be written into the journal. That way, expensive filesystem operations are avoided if the transaction ends up being a no-op. check-in: b78e58ae user: drh tags: trunk
13:59
Rewrite a couple of queries used internally by FTS3 to take advantage of the "SELECT max(x) FROM ..." optimization. check-in: b7e42ae7 user: dan tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/pager.c.

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      }
    }

#ifdef SQLITE_CHECK_PAGES
    sqlite3PcacheIterateDirty(pPager->pPCache, pager_set_pagehash);
#endif

    sqlite3PcacheCleanAll(pPager->pPCache);
    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;
    pPager->nRec = 0;
  }


  if( !pPager->exclusiveMode ){
    rc2 = osUnlock(pPager->fd, SHARED_LOCK);
    pPager->state = PAGER_SHARED;
    pPager->changeCountDone = 0;
  }else if( pPager->state==PAGER_SYNCED ){
    pPager->state = PAGER_EXCLUSIVE;
................................................................................
    if( rc==SQLITE_OK ){
      pPager->state = PAGER_RESERVED;
      if( exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }

    /* If the required locks were successfully obtained, open the journal
    ** file and write the first journal-header to it.


    */
    if( rc==SQLITE_OK && pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
      rc = pager_open_journal(pPager);
    }
  }else if( isOpen(pPager->jfd) && pPager->journalOff==0 ){
    /* This happens when the pager was in exclusive-access mode the last
    ** time a (read or write) transaction was successfully concluded
    ** by this connection. Instead of deleting the journal file it was 
    ** kept open and either was truncated to 0 bytes or its header was
    ** overwritten with zeros.
    */
................................................................................
    assert( pPager->nRec==0 );
    assert( pPager->dbOrigSize==0 );
    assert( pPager->pInJournal==0 );
    rc = pager_open_journal(pPager);
  }

  PAGERTRACE(("TRANSACTION %d\n", PAGERID(pPager)));
  assert( !isOpen(pPager->jfd) || pPager->journalOff>0 || rc!=SQLITE_OK );
  if( rc!=SQLITE_OK ){
    assert( !pPager->dbModified );
    /* Ignore any IO error that occurs within pager_end_transaction(). The
    ** purpose of this call is to reset the internal state of the pager
    ** sub-system. It doesn't matter if the journal-file is not properly
    ** finalized at this point (since it is not a valid journal file anyway).
    */
................................................................................
  }else{

    /* If we get this far, it means that the page needs to be
    ** written to the transaction journal or the ckeckpoint journal
    ** or both.
    **
    ** Higher level routines should have already started a transaction,
    ** which means they have acquired the necessary locks and opened
    ** a rollback journal.  Double-check to makes sure this is the case.
    */
    rc = sqlite3PagerBegin(pPager, 0, pPager->subjInMemory);
    if( NEVER(rc!=SQLITE_OK) ){
      return rc;
    }
    if( !isOpen(pPager->jfd) && pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
      assert( pPager->useJournal );
      rc = pager_open_journal(pPager);
      if( rc!=SQLITE_OK ) return rc;
    }
................................................................................
  int rc = SQLITE_OK;                       /* Return code */
  int nCurrent = pPager->nSavepoint;        /* Current number of savepoints */

  if( nSavepoint>nCurrent && pPager->useJournal ){
    int ii;                                 /* Iterator variable */
    PagerSavepoint *aNew;                   /* New Pager.aSavepoint array */

    /* Either there is no active journal or the sub-journal is open or 
    ** the journal is always stored in memory */
    assert( pPager->nSavepoint==0 || isOpen(pPager->sjfd) ||
            pPager->journalMode==PAGER_JOURNALMODE_MEMORY );

    /* Grow the Pager.aSavepoint array using realloc(). Return SQLITE_NOMEM
    ** if the allocation fails. Otherwise, zero the new portion in case a 
    ** malloc failure occurs while populating it in the for(...) loop below.
    */
    aNew = (PagerSavepoint *)sqlite3Realloc(
        pPager->aSavepoint, sizeof(PagerSavepoint)*nSavepoint
    );
................................................................................
    pPager->aSavepoint = aNew;
    pPager->nSavepoint = nSavepoint;

    /* Populate the PagerSavepoint structures just allocated. */
    for(ii=nCurrent; ii<nSavepoint; ii++){
      assert( pPager->dbSizeValid );
      aNew[ii].nOrig = pPager->dbSize;
      if( isOpen(pPager->jfd) && ALWAYS(pPager->journalOff>0) ){
        aNew[ii].iOffset = pPager->journalOff;
      }else{
        aNew[ii].iOffset = JOURNAL_HDR_SZ(pPager);
      }
      aNew[ii].iSubRec = pPager->nSubRec;
      aNew[ii].pInSavepoint = sqlite3BitvecCreate(pPager->dbSize);
      if( !aNew[ii].pInSavepoint ){
................................................................................
              || eMode==PAGER_JOURNALMODE_OFF)
   && !pPager->dbModified
   && (!isOpen(pPager->jfd) || 0==pPager->journalOff)
  ){
    if( isOpen(pPager->jfd) ){
      sqlite3OsClose(pPager->jfd);
    }









    pPager->journalMode = (u8)eMode;
  }
  return (int)pPager->journalMode;
}

/*
** Get/set the size-limit used for persistent journal files.







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      }
    }

#ifdef SQLITE_CHECK_PAGES
    sqlite3PcacheIterateDirty(pPager->pPCache, pager_set_pagehash);
#endif


    sqlite3BitvecDestroy(pPager->pInJournal);
    pPager->pInJournal = 0;
    pPager->nRec = 0;
  }
  sqlite3PcacheCleanAll(pPager->pPCache);

  if( !pPager->exclusiveMode ){
    rc2 = osUnlock(pPager->fd, SHARED_LOCK);
    pPager->state = PAGER_SHARED;
    pPager->changeCountDone = 0;
  }else if( pPager->state==PAGER_SYNCED ){
    pPager->state = PAGER_EXCLUSIVE;
................................................................................
    if( rc==SQLITE_OK ){
      pPager->state = PAGER_RESERVED;
      if( exFlag ){
        rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
      }
    }

    /* No need to open the journal file at this time.  It will be
    ** opened before it is written to.  If we defer opening the journal,
    ** we might save the work of creating a file if the transaction
    ** ends up being a no-op.
    */



  }else if( isOpen(pPager->jfd) && pPager->journalOff==0 ){
    /* This happens when the pager was in exclusive-access mode the last
    ** time a (read or write) transaction was successfully concluded
    ** by this connection. Instead of deleting the journal file it was 
    ** kept open and either was truncated to 0 bytes or its header was
    ** overwritten with zeros.
    */
................................................................................
    assert( pPager->nRec==0 );
    assert( pPager->dbOrigSize==0 );
    assert( pPager->pInJournal==0 );
    rc = pager_open_journal(pPager);
  }

  PAGERTRACE(("TRANSACTION %d\n", PAGERID(pPager)));

  if( rc!=SQLITE_OK ){
    assert( !pPager->dbModified );
    /* Ignore any IO error that occurs within pager_end_transaction(). The
    ** purpose of this call is to reset the internal state of the pager
    ** sub-system. It doesn't matter if the journal-file is not properly
    ** finalized at this point (since it is not a valid journal file anyway).
    */
................................................................................
  }else{

    /* If we get this far, it means that the page needs to be
    ** written to the transaction journal or the ckeckpoint journal
    ** or both.
    **
    ** Higher level routines should have already started a transaction,
    ** which means they have acquired the necessary locks but the rollback
    ** journal might not yet be open.
    */
    rc = sqlite3PagerBegin(pPager, 0, pPager->subjInMemory);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    if( !isOpen(pPager->jfd) && pPager->journalMode!=PAGER_JOURNALMODE_OFF ){
      assert( pPager->useJournal );
      rc = pager_open_journal(pPager);
      if( rc!=SQLITE_OK ) return rc;
    }
................................................................................
  int rc = SQLITE_OK;                       /* Return code */
  int nCurrent = pPager->nSavepoint;        /* Current number of savepoints */

  if( nSavepoint>nCurrent && pPager->useJournal ){
    int ii;                                 /* Iterator variable */
    PagerSavepoint *aNew;                   /* New Pager.aSavepoint array */






    /* Grow the Pager.aSavepoint array using realloc(). Return SQLITE_NOMEM
    ** if the allocation fails. Otherwise, zero the new portion in case a 
    ** malloc failure occurs while populating it in the for(...) loop below.
    */
    aNew = (PagerSavepoint *)sqlite3Realloc(
        pPager->aSavepoint, sizeof(PagerSavepoint)*nSavepoint
    );
................................................................................
    pPager->aSavepoint = aNew;
    pPager->nSavepoint = nSavepoint;

    /* Populate the PagerSavepoint structures just allocated. */
    for(ii=nCurrent; ii<nSavepoint; ii++){
      assert( pPager->dbSizeValid );
      aNew[ii].nOrig = pPager->dbSize;
      if( isOpen(pPager->jfd) && pPager->journalOff>0 ){
        aNew[ii].iOffset = pPager->journalOff;
      }else{
        aNew[ii].iOffset = JOURNAL_HDR_SZ(pPager);
      }
      aNew[ii].iSubRec = pPager->nSubRec;
      aNew[ii].pInSavepoint = sqlite3BitvecCreate(pPager->dbSize);
      if( !aNew[ii].pInSavepoint ){
................................................................................
              || eMode==PAGER_JOURNALMODE_OFF)
   && !pPager->dbModified
   && (!isOpen(pPager->jfd) || 0==pPager->journalOff)
  ){
    if( isOpen(pPager->jfd) ){
      sqlite3OsClose(pPager->jfd);
    }
    assert( (PAGER_JOURNALMODE_TRUNCATE & 1)==1 );
    assert( (PAGER_JOURNALMODE_PERSIST & 1)==1 );
    assert( (PAGER_JOURNALMODE_DELETE & 1)==0 );
    assert( (PAGER_JOURNALMODE_MEMORY & 1)==0 );
    assert( (PAGER_JOURNALMODE_OFF & 1)==0 );
    if( (pPager->journalMode & 1)==1 && (eMode & 1)==0
         && !pPager->exclusiveMode ){
      sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
    }
    pPager->journalMode = (u8)eMode;
  }
  return (int)pPager->journalMode;
}

/*
** Get/set the size-limit used for persistent journal files.

Changes to test/jrnlmode.test.

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    do_test jrnlmode-6.5 {
      execsql {
        PRAGMA journal_mode = MEMORY;
        BEGIN;
          INSERT INTO t4 VALUES(3, 4);
      }
      file exists test.db-journal
    } {1}
    do_test jrnlmode-6.7 {
      execsql {
        COMMIT;
        SELECT * FROM t4;
      }
    } {1 2 3 4}
    do_test jrnlmode-6.8 {
      file exists test.db-journal
    } {1}
    do_test jrnlmode-6.9 {
      execsql {
        PRAGMA journal_mode = DELETE;
        BEGIN IMMEDIATE; COMMIT;
      }
      file exists test.db-journal
    } {0}
  }
}

finish_test







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    do_test jrnlmode-6.5 {
      execsql {
        PRAGMA journal_mode = MEMORY;
        BEGIN;
          INSERT INTO t4 VALUES(3, 4);
      }
      file exists test.db-journal
    } {0}
    do_test jrnlmode-6.7 {
      execsql {
        COMMIT;
        SELECT * FROM t4;
      }
    } {1 2 3 4}
    do_test jrnlmode-6.8 {
      file exists test.db-journal
    } {0}
    do_test jrnlmode-6.9 {
      execsql {
        PRAGMA journal_mode = DELETE;
        BEGIN IMMEDIATE; INSERT INTO t4 VALUES(1,2); COMMIT;
      }
      file exists test.db-journal
    } {0}
  }
}

finish_test

Changes to test/misc1.test.

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#
do_test misc1-14.1 {
  file mkdir tempdir
  cd tempdir
  execsql {BEGIN}
  file exists ./test.db-journal
} {0}
do_test misc1-14.2 {
  execsql {UPDATE t1 SET a=0 WHERE 0}




  file exists ../test.db-journal
} {1}
do_test misc1-14.3 {
  cd ..
  file delete -force tempdir
  execsql {COMMIT}
  file exists ./test.db-journal







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#
do_test misc1-14.1 {
  file mkdir tempdir
  cd tempdir
  execsql {BEGIN}
  file exists ./test.db-journal
} {0}
do_test misc1-14.2a {
  execsql {UPDATE t1 SET a=a||'x' WHERE 0}
  file exists ../test.db-journal
} {0}
do_test misc1-14.2b {
  execsql {UPDATE t1 SET a=a||'y' WHERE 1}
  file exists ../test.db-journal
} {1}
do_test misc1-14.3 {
  cd ..
  file delete -force tempdir
  execsql {COMMIT}
  file exists ./test.db-journal