diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/pager.c | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/src/pager.c b/src/pager.c index 9949c11f4..c4c785147 100644 --- a/src/pager.c +++ b/src/pager.c @@ -18,7 +18,7 @@ ** file simultaneously, or one process from reading the database while ** another is writing. ** -** @(#) $Id: pager.c,v 1.587 2009/05/13 07:52:06 danielk1977 Exp $ +** @(#) $Id: pager.c,v 1.588 2009/05/29 00:30:30 drh Exp $ */ #ifndef SQLITE_OMIT_DISKIO #include "sqliteInt.h" @@ -3384,18 +3384,31 @@ static int hasHotJournal(Pager *pPager, int *pExists){ rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists); if( rc==SQLITE_OK && exists ){ int locked; /* True if some process holds a RESERVED lock */ + + /* Race condition here: Another process might have been holding the + ** the RESERVED lock and have a journal open at the sqlite3OsAccess() + ** call above, but then delete the journal and drop the lock before + ** we get to the following sqlite3OsCheckReservedLock() call. If that + ** is the case, this routine might think there is a hot journal when + ** in fact there is none. This results in a false-positive which will + ** be dealt with by the playback routine under. Ticket #3883. + */ rc = sqlite3OsCheckReservedLock(pPager->fd, &locked); if( rc==SQLITE_OK && !locked ){ int nPage; /* Check the size of the database file. If it consists of 0 pages, ** then delete the journal file. See the header comment above for - ** the reasoning here. + ** the reasoning here. Delete the obsolete journal file under + ** a RESERVED lock to avoid race conditions. */ rc = sqlite3PagerPagecount(pPager, &nPage); if( rc==SQLITE_OK ){ if( nPage==0 ){ - rc = sqlite3OsDelete(pVfs, pPager->zJournal, 0); + if( sqlite3OsLock(pPager->fd, RESERVED_LOCK)==SQLITE_OK ){ + sqlite3OsDelete(pVfs, pPager->zJournal, 0); + sqlite3OsUnlock(pPager->fd, SHARED_LOCK); + } }else{ /* The journal file exists and no other connection has a reserved ** or greater lock on the database file. Now check that there is @@ -3413,6 +3426,18 @@ static int hasHotJournal(Pager *pPager, int *pExists){ } sqlite3OsClose(pPager->jfd); *pExists = (first!=0); + }else{ + /* If we cannot open the rollback journal file in order to see if + ** its has a zero header, that might be due to an I/O error, or + ** it might be due to the race condition described above and in + ** ticket #3883. Either way, assume that the journal is hot. + ** This might be a false positive. But if it is, then the + ** automatic journal playback and recovery mechanism will deal + ** with it under an EXCLUSIVE lock where we do not need to + ** worry so much with race conditions. + */ + *pExists = 1; + rc = SQLITE_OK; } } } |