d58734d781
There were two separate Atomic_counter<uint32_t>, purge_sys.m_SYS_paused and purge_sys.m_FTS_paused. In purge_sys.wait_FTS() we have to read both atomically. We used to use an overkill solution for this, acquiring purge_sys.latch and waiting 10 milliseconds between samples. To make matters worse, the 10-millisecond wait was unconditional, which would unnecessarily suspend the purge_coordinator_task every now and then. It turns out that we can fold both "reference counts" into a single Atomic_relaxed<uint32_t> and avoid the purge_sys.latch. To assess whether std::memory_order_relaxed is acceptable, we should consider the operations that read these "reference counts", that is, purge_sys_t::wait_FTS(bool) and purge_sys_t::must_wait_FTS(). Outside debug assertions, purge_sys.must_wait_FTS() is only invoked in trx_purge_table_acquire(), which is covered by a shared dict_sys.latch. We would increment the counter as part of a DDL operation, but before acquiring an exclusive dict_sys.latch. So, a purge_sys_t::close_and_reopen() loop could be triggered slightly prematurely, before a problematic DDL operation is actually executed. Decrementing the counter is less of an issue; purge_sys.resume_FTS() or purge_sys.resume_SYS() would mostly be invoked while holding an exclusive dict_sys.latch; ha_innobase::delete_table() does it outside that critical section. Still, this would only cause some extra wait in the purge_coordinator_task, just like at the start of a DDL operation. There are two calls to purge_sys_t::wait_FTS(bool): in the above mentioned purge_sys_t::close_and_reopen() and in purge_sys_t::clone_oldest_view(), both invoked by the purge_coordinator_task. There is also a purge_sys.clone_oldest_view<true>() call at startup when no DDL operation can be in progress. purge_sys_t::m_SYS_paused: Merged into m_FTS_paused, using a new multiplier PAUSED_SYS = 65536. purge_sys_t::wait_FTS(): Remove an unnecessary sleep as well as the access to purge_sys.latch. It suffices to poll purge_sys.m_FTS_paused. purge_sys_t::stop_FTS(): Do not acquire purge_sys.latch. Reviewed by: Debarun Banerjee |
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VERSION |
Code status:
MariaDB: The innovative open source 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/
Getting the code, building it and testing it
Refer to the following guide: https://mariadb.org/get-involved/getting-started-for-developers/get-code-build-test/ which outlines how to build the source code correctly and run the MariaDB testing framework, as well as which branch to target for your contributions.
Help
More help is available from the Maria Discuss mailing list https://lists.mariadb.org/postorius/lists/discuss.lists.mariadb.org/ and MariaDB's Zulip instance, https://mariadb.zulipchat.com/
Licensing
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