-----Original Message----- From: MARK CALLAGHAN To: maria-developers@lists.launchpad.net Sent: Sat, 28 Feb 2009 10:41 pm Subject: [Maria-developers] safe patches to backport -- pool-of-threads One of the features listed here http://askmonty.org/wiki/index.php/MariaDB_versus_MySQL as a potential backport is support for pool-of-threads. I am not sure how safe this feature is today. http://mysqlha.blogspot.com/2009/01/no-new-global-mutexes-and-how-to-make.ht... describes some of the problems that might cause a server to hang when pool-of-threads is used. http://bugs.mysql.com/bug.php?id=42288 describes the performance overhead of pool-of-threads. The overhead is significant for workloads with fast queries such as sysbench. I think that pool-of-threads needs a lot of work before it can be considered safe. We backported this to our 5.0 branch at work and have begun to search for fixes. -- Mark Callaghan mdcallag@gmail.com _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : maria-developers@lists.launchpad.net Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp One way to deal with the overhead of the thread pool is to support multiple thread pools. The selection of which connection goes to which pool could be based more than just on listening port value. Ideally each pool would have its own connection listener/ request assembly thread, distinct from the connection manager thread(s) listening on ports. The thread pool selection could be based on some rules like 'everything from user X goes to pool Y'. The rules could be stored in a dictionary table. The documentation is wrong IMO in that pool-of-threads makes innodb_thread_concurrency control unnecessary. If the workload calls for setting innodb_thread_concurrency=4 then it has to be 4, thread pool or not. There's an obvious problem that in this case you may end up with all 20 threads in pool-of-threads either doing the innodb stuff or waiting on entering innodb, then new connections cannot be serviced even if they wouldn't use InnoDB. Again multiple thread pools could help here. Michael Izioumtchenko mizioumt@netscape.net The opinion(s) stated above, if any, are mine and don't necessarily reflect those of my employer