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.html

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



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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