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Change the pager locking mechanism so that we don't have to write page 1

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to the journal and to the database unless it actually changes. (CVS 419)

FossilOrigin-Name: 480eef1a3a4f049bc0d0cbee32dc8a8d138597c6
This commit is contained in:
drh
2002-03-05 12:41:19 +00:00
parent 603240cf5d
commit 4b845d7ef4
6 changed files with 155 additions and 105 deletions
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97
src/pager.c
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@@ -18,7 +18,7 @@
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.42 2002/03/05 01:11:14 drh Exp $
** @(#) $Id: pager.c,v 1.43 2002/03/05 12:41:20 drh Exp $
*/
#include "sqliteInt.h"
#include "pager.h"
@@ -988,6 +988,63 @@ int sqlitepager_unref(void *pData){
return SQLITE_OK;
}
/*
** Acquire a write-lock on the database. The lock is removed when
** the any of the following happen:
**
** * sqlitepager_commit() is called.
** * sqlitepager_rollback() is called.
** * sqlitepager_close() is called.
** * sqlitepager_unref() is called to on every outstanding page.
**
** The parameter to this routine is a pointer to any open page of the
** database file. Nothing changes about the page - it is used merely
** to acquire a pointer to the Pager structure and as proof that there
** is already a read-lock on the database.
**
** If the database is already write-locked, this routine is a no-op.
*/
int sqlitepager_begin(void *pData){
PgHdr *pPg = DATA_TO_PGHDR(pData);
Pager *pPager = pPg->pPager;
int rc = SQLITE_OK;
assert( pPg->nRef>0 );
assert( pPager->state!=SQLITE_UNLOCK );
if( pPager->state==SQLITE_READLOCK ){
assert( pPager->aInJournal==0 );
rc = sqliteOsWriteLock(&pPager->fd);
if( rc!=SQLITE_OK ){
return rc;
}
pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
if( pPager->aInJournal==0 ){
sqliteOsReadLock(&pPager->fd);
return SQLITE_NOMEM;
}
rc = sqliteOsOpenExclusive(pPager->zJournal, &pPager->jfd, 0);
if( rc!=SQLITE_OK ){
sqliteFree(pPager->aInJournal);
pPager->aInJournal = 0;
sqliteOsReadLock(&pPager->fd);
return SQLITE_CANTOPEN;
}
pPager->journalOpen = 1;
pPager->needSync = !pPager->noSync;
pPager->state = SQLITE_WRITELOCK;
sqlitepager_pagecount(pPager);
pPager->origDbSize = pPager->dbSize;
rc = sqliteOsWrite(&pPager->jfd, aJournalMagic, sizeof(aJournalMagic));
if( rc==SQLITE_OK ){
rc = sqliteOsWrite(&pPager->jfd, &pPager->dbSize, sizeof(Pgno));
}
if( rc!=SQLITE_OK ){
rc = pager_unwritelock(pPager);
if( rc==SQLITE_OK ) rc = SQLITE_FULL;
}
}
return rc;
}
/*
** Mark a data page as writeable. The page is written into the journal
** if it is not there already. This routine must be called before making
@@ -1035,39 +1092,8 @@ int sqlitepager_write(void *pData){
** create it if it does not.
*/
assert( pPager->state!=SQLITE_UNLOCK );
if( pPager->state==SQLITE_READLOCK ){
assert( pPager->aInJournal==0 );
rc = sqliteOsWriteLock(&pPager->fd);
if( rc!=SQLITE_OK ){
return rc;
}
pPager->aInJournal = sqliteMalloc( pPager->dbSize/8 + 1 );
if( pPager->aInJournal==0 ){
sqliteOsReadLock(&pPager->fd);
return SQLITE_NOMEM;
}
rc = sqliteOsOpenExclusive(pPager->zJournal, &pPager->jfd, 0);
if( rc!=SQLITE_OK ){
sqliteFree(pPager->aInJournal);
pPager->aInJournal = 0;
sqliteOsReadLock(&pPager->fd);
return SQLITE_CANTOPEN;
}
pPager->journalOpen = 1;
pPager->needSync = 0;
pPager->state = SQLITE_WRITELOCK;
sqlitepager_pagecount(pPager);
pPager->origDbSize = pPager->dbSize;
rc = sqliteOsWrite(&pPager->jfd, aJournalMagic, sizeof(aJournalMagic));
if( rc==SQLITE_OK ){
rc = sqliteOsWrite(&pPager->jfd, &pPager->dbSize, sizeof(Pgno));
}
if( rc!=SQLITE_OK ){
rc = pager_unwritelock(pPager);
if( rc==SQLITE_OK ) rc = SQLITE_FULL;
return rc;
}
}
rc = sqlitepager_begin(pData);
if( rc!=SQLITE_OK ) return rc;
assert( pPager->state==SQLITE_WRITELOCK );
assert( pPager->journalOpen );
@@ -1247,6 +1273,9 @@ commit_abort:
int sqlitepager_rollback(Pager *pPager){
int rc;
if( pPager->errMask!=0 && pPager->errMask!=PAGER_ERR_FULL ){
if( pPager->state>=SQLITE_WRITELOCK ){
pager_playback(pPager);
}
return pager_errcode(pPager);
}
if( pPager->state!=SQLITE_WRITELOCK ){