[DOC] Missing explanation for the innodb_thread_concurrency_timer_based variable

[Volans]

[In:Percona Server Documentation]

In the "InnoDB timer-based Concurrency Throttling" ( http://www.percona.com/doc/percona-server/5.5/performance/innodb_thread_concurrency_timer_based.html ) page the explanation of the variable "innodb_thread_concurrency_timer_based" is missing.

Is this variable used in some way, maybe the same explained in the MySQL 5.4 older documentation (see http://mysql.localhost.net.ar/doc/mysql-5.4-features/en/smp-improvements.html ) or it is not used anymore as indicated in bug #695911 ?

[Raghavendra D Prabhu (raghavendra-prabhu)]

That variable is still there (it was not removed in 695911) but its validity is slightly different from the 5.4 documentatation. Innodb_have_sync_atomic is no longer there, but Innodb_have_atomic_builtins is ON or OFF based on whether the InnoDB has been built with atomic builtins or not. If Innodb_have_atomic_builtins is OFF, then innodb_thread_concurrency_timer_based won't have any effect, otherwise turning it OFF / ON changes the algorithm when dealing with multiple threads in InnoDB kernel.

[Raghavendra D Prabhu (raghavendra-prabhu)]

The other detail about "The lock-free concurrency method also requires that innodb_thread_concurrency be set to a value greater than 0 (the default value in 5.4). " still holds though.

[Laurynas Biveinis (laurynas-biveinis)]

All interesting platforms do have the atomic builtins, we can only consider that case for performance. The explanation should be expanded what the variable actually does.

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-1930