b07beff894
MySQL 5.7.9 (and MariaDB 10.2.2) introduced a race condition between InnoDB transaction commit and the conversion of implicit locks into explicit ones. The assertion failure can be triggered with a test that runs 3 concurrent single-statement transactions in a loop on a simple table: CREATE TABLE t (a INT PRIMARY KEY) ENGINE=InnoDB; thread1: INSERT INTO t SET a=1; thread2: DELETE FROM t; thread3: SELECT * FROM t FOR UPDATE; -- or DELETE FROM t; The failure scenarios are like the following: (1) The INSERT statement is being committed, waiting for lock_sys->mutex. (2) At the time of the failure, both the DELETE and SELECT transactions are active but have not logged any changes yet. (3) The transaction where the !other_lock assertion fails started lock_rec_convert_impl_to_expl(). (4) After this point, the commit of the INSERT removed the transaction from trx_sys->rw_trx_set, in trx_erase_lists(). (5) The other transaction consulted trx_sys->rw_trx_set and determined that there is no implicit lock. Hence, it grabbed the lock. (6) The !other_lock assertion fails in lock_rec_add_to_queue() for the lock_rec_convert_impl_to_expl(), because the lock was 'stolen'. This assertion failure looks genuine, because the INSERT transaction is still active (trx->state=TRX_STATE_ACTIVE). The problematic step (4) was introduced in mysql/mysql-server@e27e0e0bb7 which fixed something related to MVCC (covered by the test innodb.innodb-read-view). Basically, it reintroduced an error that had been mentioned in an earlier commit mysql/mysql-server@a17be6963f: "The active transaction was removed from trx_sys->rw_trx_set prematurely." Our fix goes along the following lines: (a) Implicit locks will released by assigning trx->state=TRX_STATE_COMMITTED_IN_MEMORY as the first step. This transition will no longer be protected by lock_sys_t::mutex, only by trx->mutex. This idea is by Sergey Vojtovich. (b) We detach the transaction from trx_sys before starting to release explicit locks. (c) All callers of trx_rw_is_active() and trx_rw_is_active_low() must recheck trx->state after acquiring trx->mutex. (d) Before releasing any explicit locks, we will ensure that any activity by other threads to convert implicit locks into explicit will have ceased, by checking !trx_is_referenced(trx). There was a glitch in this check when it was part of lock_trx_release_locks(); at the end we would release trx->mutex and acquire lock_sys->mutex and trx->mutex, and fail to recheck (trx_is_referenced() is protected by trx_t::mutex). (e) Explicit locks can be released in batches (LOCK_RELEASE_INTERVAL=1000) just like we did before. trx_t::state: Document that the transition to COMMITTED is only protected by trx_t::mutex, no longer by lock_sys_t::mutex. trx_rw_is_active_low(), trx_rw_is_active(): Document that the transaction state should be rechecked after acquiring trx_t::mutex. trx_t::commit_state(): New function to change a transaction to committed state, to release implicit locks. trx_t::release_locks(): New function to release the explicit locks after commit_state(). lock_trx_release_locks(): Move much of the logic to the caller (which must invoke trx_t::commit_state() and trx_t::release_locks() as needed), and assert that the transaction will have locks. trx_get_trx_by_xid(): Make the parameter a pointer to const. lock_rec_other_trx_holds_expl(): Recheck trx->state after acquiring trx->mutex, and avoid a redundant lookup of the transaction. lock_rec_queue_validate(): Recheck impl_trx->state while holding impl_trx->mutex. row_vers_impl_x_locked(), row_vers_impl_x_locked_low(): Document that the transaction state must be rechecked after trx_mutex_enter(). trx_free_prepared(): Adjust for the changes to lock_trx_release_locks(). |
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| BUILD | ||
| client | ||
| cmake | ||
| dbug | ||
| debian | ||
| Docs | ||
| extra | ||
| include | ||
| libmariadb@544b6f1d12 | ||
| libmysqld | ||
| libservices | ||
| man | ||
| mysql-test | ||
| mysys | ||
| mysys_ssl | ||
| pcre | ||
| plugin | ||
| randgen/conf | ||
| scripts | ||
| sql | ||
| sql-bench | ||
| sql-common | ||
| storage | ||
| strings | ||
| support-files | ||
| tests | ||
| unittest | ||
| vio | ||
| win | ||
| wsrep | ||
| zlib | ||
| .clang-format | ||
| .gitattributes | ||
| .gitignore | ||
| .gitmodules | ||
| .travis.compiler.sh | ||
| .travis.yml | ||
| appveyor.yml | ||
| BUILD-CMAKE | ||
| CMakeLists.txt | ||
| config.h.cmake | ||
| configure.cmake | ||
| COPYING | ||
| CREDITS | ||
| EXCEPTIONS-CLIENT | ||
| INSTALL-SOURCE | ||
| INSTALL-WIN-SOURCE | ||
| KNOWN_BUGS.txt | ||
| README.md | ||
| THIRDPARTY | ||
| VERSION | ||
Code status:
travis-ci.org (10.2 branch)ci.appveyor.com
MariaDB: drop-in replacement for MySQL
MariaDB is designed as a drop-in replacement of MySQL(R) with more features, new storage engines, fewer bugs, and better performance.
MariaDB is brought to you by the MariaDB Foundation. Please read the CREDITS file for details about the MariaDB Foundation, and who is developing MariaDB.
MariaDB is developed by many of the original developers of MySQL who now work for the MariaDB Foundation and the MariaDB Corporation, and by many people in the community.
MySQL, which is the base of MariaDB, is a product and trademark of Oracle Corporation, Inc. For a list of developers and other contributors, see the Credits appendix. You can also run 'SHOW authors' to get a list of active contributors.
A description of the MariaDB project and a manual can be found at:
https://mariadb.com/kb/en/mariadb-vs-mysql-features/
https://mariadb.com/kb/en/mariadb-versus-mysql-features/
https://mariadb.com/kb/en/mariadb-versus-mysql-compatibility/
As MariaDB is a full replacement of MySQL, the MySQL manual at http://dev.mysql.com/doc is generally applicable.
Help:
More help is available from the Maria Discuss mailing list https://launchpad.net/~maria-discuss and the #maria IRC channel on Freenode.
Licensing:
NOTE:
MariaDB is specifically available only under version 2 of the GNU General Public License (GPLv2). (I.e. Without the "any later version" clause.) This is inherited from MySQL. Please see the README file in the MySQL distribution for more information.
License information can be found in the COPYING file. Third party license information can be found in the THIRDPARTY file.
Bug Reports:
Bug and/or error reports regarding MariaDB should be submitted at: https://jira.mariadb.org
For reporting security vulnerabilities see: https://mariadb.org/about/security-policy/
Bugs in the MySQL code can also be submitted at: https://bugs.mysql.com
The code for MariaDB, including all revision history, can be found at: https://github.com/MariaDB/server
Code status:
- travis-ci.org (10.2 branch)