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If, after obtaining a SHARED lock, there exists a *-wal file in the file-system, use WAL mode. This is necessary to recover from a crash that damages the first page of the database file.

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FossilOrigin-Name: 33cabf271b8f4dda508a610bf59964273fe2cb84
This commit is contained in:
dan
2010-04-21 11:43:38 +00:00
parent 28e5386f79
commit a470aeb4ac
6 changed files with 138 additions and 59 deletions
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109
src/pager.c
View File

@@ -491,6 +491,16 @@ static int assert_pager_state(Pager *pPager){
}
#endif
#ifndef NDEBUG
static void assert_file_lock(Pager *pPager, int eLock){
int locktype;
sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_LOCKSTATE, &locktype);
assert( locktype==eLock );
}
#else
# define assert_file_lock(x,y)
#endif
/*
** Return true if it is necessary to write page *pPg into the sub-journal.
@@ -3726,6 +3736,59 @@ static int hasHotJournal(Pager *pPager, int *pExists){
return rc;
}
/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists. Assuming no error occurs, set *pExists to 1 if the file exists,
** or 0 otherwise and return SQLITE_OK. If an IO or OOM error occurs, return
** an SQLite error code.
**
** The caller must hold a SHARED lock on the database file to call this
** function.
*/
static int pagerHasWAL(Pager *pPager, int *pExists){
int rc; /* Return code */
/* Check that a SHARED lock is held on the database file. Because an
** EXCLUSIVE lock on the db file is required to delete a WAL, this
** ensures there is no race condition between the xAccess() below and
** an xDelete() being executed by some other connection.
*/
assert_file_lock(pPager, SQLITE_LOCK_SHARED);
if( !pPager->tempFile ){
char *zLog = sqlite3_mprintf("%s-wal", pPager->zFilename);
if( !zLog ){
rc = SQLITE_NOMEM;
}else{
rc = sqlite3OsAccess(pPager->pVfs, zLog, SQLITE_ACCESS_EXISTS, pExists);
sqlite3_free(zLog);
}
}else{
rc = SQLITE_OK;
*pExists = 0;
}
return rc;
}
static int pagerOpenSnapshot(Pager *pPager){
int rc;
int changed;
assert( pagerUseLog(pPager) );
rc = sqlite3LogOpenSnapshot(pPager->pLog, &changed);
if( rc==SQLITE_OK ){
int dummy;
if( changed ){
pager_reset(pPager);
assert( pPager->errCode || pPager->dbSizeValid==0 );
}
rc = sqlite3PagerPagecount(pPager, &dummy);
}
pPager->state = PAGER_SHARED;
return rc;
}
/*
** This function is called to obtain a shared lock on the database file.
@@ -3781,23 +3844,11 @@ int sqlite3PagerSharedLock(Pager *pPager){
}
if( pagerUseLog(pPager) ){
int changed = 0; /* True if the cache must be flushed */
/* 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 );
}
rc = sqlite3PagerPagecount(pPager, &dummy);
}
pPager->state = PAGER_SHARED;
rc = pagerOpenSnapshot(pPager);
}else if( pPager->state==PAGER_UNLOCK || isErrorReset ){
sqlite3_vfs * const pVfs = pPager->pVfs;
int isHotJournal = 0;
int isWal = 0;
assert( !MEMDB );
assert( sqlite3PcacheRefCount(pPager->pPCache)==0 );
if( pPager->noReadlock ){
@@ -3952,7 +4003,17 @@ int sqlite3PagerSharedLock(Pager *pPager){
}
assert( pPager->exclusiveMode || pPager->state==PAGER_SHARED );
if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
rc = pagerHasWAL(pPager, &isWal);
if( rc!=SQLITE_OK ){
goto failed;
}
if( isWal ){
pager_reset(pPager);
rc = sqlite3PagerOpenLog(pPager, 0);
if( rc==SQLITE_OK ){
rc = pagerOpenSnapshot(pPager);
}
}else if( pPager->journalMode==PAGER_JOURNALMODE_WAL ){
pPager->journalMode = PAGER_JOURNALMODE_DELETE;
}
}
@@ -5675,13 +5736,7 @@ int sqlite3PagerLogCallback(Pager *pPager){
int sqlite3PagerOpenLog(Pager *pPager, int *pisOpen){
int rc = SQLITE_OK; /* Return code */
#ifdef SQLITE_DEBUG
int locktype;
sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_LOCKSTATE, &locktype);
assert( locktype==SQLITE_LOCK_SHARED );
assert( pPager->state>=PAGER_SHARED );
#endif
assert_file_lock(pPager, SQLITE_LOCK_SHARED);
if( !pPager->pLog ){
/* Open the connection to the log file. If this operation fails,
@@ -5725,15 +5780,7 @@ int sqlite3PagerCloseLog(Pager *pPager){
pPager->pLog = 0;
}
/* Make sure the EXCLUSIVE lock has not been lost somehow */
#ifdef SQLITE_DEBUG
{
int locktype;
sqlite3OsFileControl(pPager->fd, SQLITE_FCNTL_LOCKSTATE, &locktype);
assert( locktype==SQLITE_LOCK_EXCLUSIVE );
}
#endif
assert_file_lock(pPager, SQLITE_LOCK_EXCLUSIVE);
}
return rc;
}