Over the last months I’ve seen lots of customers trying to tune the thread concurrency inside MySQL with the variable thread_concurrency. Our advice is: stop wasting your time, it does nothing on GNU/Linux 🙂
Some of the biggest GNU/Linux distributions includes the variable thread_concurrency in their my.cnf file by default. One example is Debian and its variants. Furthermore the default my.cnf files of MySQL like my-large.cnf, my-innodb-heavy-4G.cnf and so on have the thread_concurrency enabled with a tune advice helping to spread the confusion:
# Try number of CPU's*2 for thread_concurrency
Don’t try it. The problems with thread_concurrency are two:
1- It’s deprecated and removed on 5.6.1
http://bugs.mysql.com/bug.php?id=55001
2- It only works on old Solaris versions https://www.percona.com/blog/2011/07/28/how-innodb-contention-may-manifest-itself/
https://www.percona.com/blog/2011/12/02/kernel_mutex-problem-cont-or-triple-your-throughput/
https://www.percona.com/blog/2010/05/24/tuning-innodb-concurrency-tickets/
innodb_thread_concurrency places a limit on the number of threads that can be running inside InnoDB. The default value in 5.5 is 0 which means “infinite number of threads” but in some workloads limiting the value can give use some performance benefits. As we always say, set up benchmark tests to identify which tuning parameters provide the most benefit to your workload.
thread_concurrency is causing lot of confusion and there are hundred of MySQL tuning howtos that explain how to tune the variable to get better performance. If you have the variable in your my.cnf don’t panic because it does nothing and you’ve only lost some of your valuable time tuning it.
+1! I see this every where on Serverfault. Every once and a while I double check
the docs because I think I’m going crazy for how often I see it …
Yep! That’s why there exists the acronym RTFM.
“This variable is specific to Solaris systems”
[http://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html#sysvar_thread_concurrency]
Good read 🙂
It was deprecated as soon as “alternate” thread library became default since Solaris9:
http://dimitrik.free.fr/db_STRESS_BMK_2008.html#note_5229
Rgds,
-Dimitri
Very clear. Shared this. Thanks!