15e889c300
The old code in prev_record_reads() did give wrong estimates when a join_buffer was used or if the table was depending on more than one other tables. When join_cache is used, it will cause a re-order of row combinations, which causes more calls to the engine for tables that are depending on tables before the join_cached one. The new prev_records_read() code provides more exact estimates and should never give a 'too low estimate', assuming that the data to the function is correct The definition of prev_record_read() is also updated. The new definition is: "Estimate the number of engine ha_index_read_calls for EQ_REF tables when taking into account the one-row-cache in join_read_always_key()" The cost of using prev_record_reads() value is changed. The value is now used similar as before to calculate the cost of the storage engine calls. However the cost of the WHERE cost is changed to take into account the total number of row combinations as the WHERE has to be checked even if the one-row-cache is used. This makes the cost slightly higher than before (for the same prev_record_reads() value). Other things: - Cached return value of prev_record_read() in best_access_path() to avoid some function calls. - Fixed bug where position[].use_join_buffer was set in best_acess_path() when join buffer was not used. This confused the semi join optimizer to try to reoptimize plans that did not need to be reoptimized. The effect of the bug fix is that we avoid doing some re-optimziations with semi-joins when join_buffer is not used. In these cases the value shown for the 'Filtering' column in EXPLAIN EXTENDED may change. - Added 'prev_record.cc' that was used to verify the logic in prev_record_reads(). Changes in test suite: - EQ_REF tables are moved up to be earlier. This is because either the higher WHERE cost when EQ_REF is used with more row combination or change of cost when using join_cache. - Filtered has changed (to the better) for some cases using semi-joins subselect_sj.test subselect_sj_jcl6.test |
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Code status:
ci.appveyor.com
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: https://mariadb.org/about/security-policy/
The code for MariaDB, including all revision history, can be found at: https://github.com/MariaDB/server