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Overview
Comment: | Modify the hasHotJournal() routine to return a false-positive if it is unable to open the journal file to check its header due to a race condition. Processing downstream of hasHotJournal() already knows how to deal with false-positives. Ticket #3883. (CVS 6687) |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | trunk |
Files: | files | file ages | folders |
SHA1: |
d6b5d8e1ab8e5d3348ace56023070271 |
User & Date: | drh 2009-05-29 00:30:30.000 |
Context
2009-05-29
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10:55 | The hasHotJournal() fix of check-in (6687) causes some minor problems in various alternative operating modes, such as locking_mode=EXCLUSIVE. This additional patch attempts to fix those concerns. Ticket #3883. (CVS 6688) (check-in: a2ba61d927 user: drh tags: trunk) | |
00:30 | Modify the hasHotJournal() routine to return a false-positive if it is unable to open the journal file to check its header due to a race condition. Processing downstream of hasHotJournal() already knows how to deal with false-positives. Ticket #3883. (CVS 6687) (check-in: d6b5d8e1ab user: drh tags: trunk) | |
2009-05-28
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21:04 | Remove references to deleted function sqlite3ExprRegister(). Changes to the expr.c source module to promote better testing. (CVS 6686) (check-in: 6ae4ad6ebe user: drh tags: trunk) | |
Changes
Changes to src/pager.c.
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14 15 16 17 18 19 20 | ** The pager is used to access a database disk file. It implements ** atomic commit and rollback through the use of a journal file that ** is separate from the database file. The pager also implements file ** locking to prevent two processes from writing the same database ** file simultaneously, or one process from reading the database while ** another is writing. ** | | | 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | ** The pager is used to access a database disk file. It implements ** atomic commit and rollback through the use of a journal file that ** is separate from the database file. The pager also implements file ** locking to prevent two processes from writing the same database ** file simultaneously, or one process from reading the database while ** another is writing. ** ** @(#) $Id: pager.c,v 1.588 2009/05/29 00:30:30 drh Exp $ */ #ifndef SQLITE_OMIT_DISKIO #include "sqliteInt.h" /* ** Macros for troubleshooting. Normally turned off */ |
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3380 3381 3382 3383 3384 3385 3386 3387 3388 3389 3390 3391 3392 | assert( isOpen(pPager->fd) ); assert( !isOpen(pPager->jfd) ); *pExists = 0; rc = sqlite3OsAccess(pVfs, pPager->zJournal, SQLITE_ACCESS_EXISTS, &exists); if( rc==SQLITE_OK && exists ){ int locked; /* True if some process holds a RESERVED lock */ 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 | > > > > > > > > > | > > | > > > > > > > > > > > > > > | 3380 3381 3382 3383 3384 3385 3386 3387 3388 3389 3390 3391 3392 3393 3394 3395 3396 3397 3398 3399 3400 3401 3402 3403 3404 3405 3406 3407 3408 3409 3410 3411 3412 3413 3414 3415 3416 3417 3418 3419 3420 3421 3422 3423 3424 3425 3426 3427 3428 3429 3430 3431 3432 3433 3434 3435 3436 3437 3438 3439 3440 3441 3442 3443 3444 3445 3446 3447 | assert( isOpen(pPager->fd) ); assert( !isOpen(pPager->jfd) ); *pExists = 0; 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. Delete the obsolete journal file under ** a RESERVED lock to avoid race conditions. */ rc = sqlite3PagerPagecount(pPager, &nPage); if( rc==SQLITE_OK ){ if( nPage==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 ** at least one non-zero bytes at the start of the journal file. ** If there is, then we consider this journal to be hot. If not, ** it can be ignored. */ int f = SQLITE_OPEN_READONLY|SQLITE_OPEN_MAIN_JOURNAL; rc = sqlite3OsOpen(pVfs, pPager->zJournal, pPager->jfd, f, &f); if( rc==SQLITE_OK ){ u8 first = 0; rc = sqlite3OsRead(pPager->jfd, (void *)&first, 1, 0); if( rc==SQLITE_IOERR_SHORT_READ ){ rc = SQLITE_OK; } 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; } } } } } return rc; |
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