ab4bfad206
* Log rows in online_alter_binlog. * Table online data is replicated within dedicated binlog file * Cached data is written on commit. * Versioning is fully supported. * Works both wit and without binlog enabled. * For now savepoints setup is forbidden while ONLINE ALTER goes on. Extra support is required. We can simply log the SAVEPOINT query events and replicate them together with row events. But it's not implemented for now. * Cache flipping: We want to care for the possible bottleneck in the online alter binlog reading/writing in advance. IO_CACHE does not provide anything better that sequential access, besides, only a single write is mutex-protected, which is not suitable, since we should write a transaction atomically. To solve this, a special layer on top Event_log is implemented. There are two IO_CACHE files underneath: one for reading, and one for writing. Once the read cache is empty, an exclusive lock is acquired (we can wait for a currently active transaction finish writing), and flip() is emitted, i.e. the write cache is reopened for read, and the read cache is emptied, and reopened for writing. This reminds a buffer flip that happens in accelerated graphics (DirectX/OpenGL/etc). Cache_flip_event_log is considered non-blocking for a single reader and a single writer in this sense, with the only lock held by reader during flip. An alternative approach by implementing a fair concurrent circular buffer is described in MDEV-24676. * Cache managers: We have two cache sinks: statement and transactional. It is important that the changes are first cached per-statement and per-transaction. If a statement fails, then only statement data is rolled back. The transaction moves along, however. Turns out, there's no guarantee that TABLE well persist in thd->open_tables to the transaction commit moment. If an error occurs, tables from statement are purged. Therefore, we can't store te caches in TABLE. Ideally, it should be handlerton, but we cut the corner and store it in THD in a list. |
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Code status:
MariaDB: The open source relational database
MariaDB was 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 and the MariaDB Corporation. 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 Corporation, the MariaDB Foundation 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-compatibility/
https://mariadb.com/kb/en/new-and-old-releases/
Help
More help is available from the Maria Discuss mailing list https://launchpad.net/~maria-discuss, MariaDB's Zulip instance, https://mariadb.zulipchat.com/
Live QA for beginner contributors
MariaDB has a dedicated time each week when we answer new contributor questions live on Zulip. From 8:00 to 10:00 UTC on Mondays, and 10:00 to 12:00 UTC on Thursdays, anyone can ask any questions they’d like, and a live developer will be available to assist.
New contributors can ask questions any time, but we will provide immediate feedback during that interval.
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 our security-policy.
The code for MariaDB, including all revision history, can be found at: https://github.com/MariaDB/server