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Enhancements to wal-mode locking scheme.

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FossilOrigin-Name: 8549c286497f3d2cd118be1334fce00d6f8a26c4
This commit is contained in:
dan
2010-04-17 12:31:37 +00:00
parent 97a313554d
commit 3de777fd8c
6 changed files with 356 additions and 260 deletions
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95
src/pager.c
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@@ -491,6 +491,7 @@ static int assert_pager_state(Pager *pPager){
}
#endif
/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
@@ -1187,19 +1188,6 @@ static int addToSavepointBitvecs(Pager *pPager, Pgno pgno){
return rc;
}
/*
** Open a connection to the write-ahead log file for pager pPager.
*/
static int pagerOpenLog(Pager *pPager){
if( !pPager->pLog ){
int rc; /* Return code from LogOpen() */
rc = sqlite3LogOpen(pPager->pVfs, pPager->zFilename, &pPager->pLog);
if( rc!=SQLITE_OK ) return rc;
}
return SQLITE_OK;
}
/*
** Return true if this pager uses a write-ahead log instead of the usual
** rollback journal. Otherwise false.
@@ -1241,8 +1229,9 @@ static void pager_unlock(Pager *pPager){
if( pagerUseLog(pPager) ){
sqlite3LogCloseSnapshot(pPager->pLog);
}else{
rc = osUnlock(pPager->fd, NO_LOCK);
}
rc = osUnlock(pPager->fd, NO_LOCK);
if( rc ){
pPager->errCode = rc;
}
@@ -3733,6 +3722,54 @@ static int hasHotJournal(Pager *pPager, int *pExists){
return rc;
}
/*
** Open a connection to the write-ahead log file for pager pPager. If
** the log connection is already open, this function is a no-op.
*/
static int pagerOpenLog(Pager *pPager){
if( !pPager->pLog ){
int rc; /* Return code */
/* Before opening the log file, obtain a SHARED lock on the database
** file. This lock will not be released until after the log file
** connection has been closed. The purpose of this lock is to stop
** any other process from unlinking the log or log-summary files while
** this connection still has them open. An EXCLUSIVE lock on the
** database file is required to unlink either of those two files.
*/
assert( pPager->state==PAGER_UNLOCK );
rc = pager_wait_on_lock(pPager, SHARED_LOCK);
if( rc!=SQLITE_OK ){
assert( pPager->state==PAGER_UNLOCK );
return pager_error(pPager, rc);
}
assert( pPager->state>=SHARED_LOCK );
/* Open the connection to the log file. If this operation fails,
** (e.g. due to malloc() failure), unlock the database file and
** return an error code.
*/
rc = sqlite3LogOpen(pPager->pVfs, pPager->zFilename, &pPager->pLog);
if( rc!=SQLITE_OK ){
osUnlock(pPager->fd, SQLITE_LOCK_NONE);
pPager->state = PAGER_UNLOCK;
return rc;
}
}else{
/* If the log file was already open, check that the pager is still holding
** the required SHARED lock on the database file.
*/
#ifdef SQLITE_DEBUG
int locktype;
sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_LOCKSTATE, &locktype);
assert( locktype==SQLITE_LOCK_SHARED );
#endif
}
return SQLITE_OK;
}
/*
** This function is called to obtain a shared lock on the database file.
** It is illegal to call sqlite3PagerAcquire() until after this function
@@ -3786,17 +3823,25 @@ int sqlite3PagerSharedLock(Pager *pPager){
pager_reset(pPager);
}
if( pagerUseLog(pPager) ){
int changed = 0;
if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
int changed = 0; /* True if the cache must be flushed */
/* Open the log file, if it is not already open. */
rc = pagerOpenLog(pPager);
if( rc!=SQLITE_OK ){
return rc;
}
/* Open a log snapshot to read from. */
rc = sqlite3LogOpenSnapshot(pPager->pLog, &changed);
if( rc==SQLITE_OK ){
int dummy;
if( changed ){
pager_reset(pPager);
assert( pPager->errCode || pPager->dbSizeValid==0 );
}
pPager->state = PAGER_SHARED; /* TODO: Is this right? */
rc = sqlite3PagerPagecount(pPager, &changed);
rc = sqlite3PagerPagecount(pPager, &dummy);
}
}else if( pPager->state==PAGER_UNLOCK || isErrorReset ){
sqlite3_vfs * const pVfs = pPager->pVfs;
@@ -5611,15 +5656,13 @@ int sqlite3PagerJournalMode(Pager *pPager, int eMode){
sqlite3OsDelete(pPager->pVfs, pPager->zJournal, 0);
}
if( eMode==PAGER_JOURNALMODE_WAL ){
int rc = pagerOpenLog(pPager);
if( rc!=SQLITE_OK ){
/* TODO: The error code should not just get dropped here. Change
** this to set a flag to force the log to be opened the first time
** it is actually required. */
return (int)pPager->journalMode;
}
/* Switching into WAL mode can only take place when no
** locks are held on the database file.
*/
if( eMode==PAGER_JOURNALMODE_WAL && pPager->state!=PAGER_UNLOCK ){
return (int)pPager->journalMode;
}
pPager->journalMode = (u8)eMode;
}
return (int)pPager->journalMode;