Heikki Tuuri wrote:
Devanada,
normally you do not need to tune this option at all.
I introduced the option when certain Linux binaries showed 'thread thrashing' at high concurrency. Setting the option to 1 or 2 could in some cases alleviate the problem.
You can experiment by setting the option to 500 to disable restrictions on concurrent operations. I am considering changing the default value to 500, because we have not seen 'thread thrashing' on any platform for a long while.
We did see something that looked a lot like this about a year ago on Mac OS X 10.3.x running InnoDB 4.0.x. Queries that normally ran fine all of a sudden started running incredibly slowly. The CPU was pinned, but things just weren't finishing in any reasonable time. Eventually InnoDB noticed some long waits and intentionally crashed itself.
Thread concurrency was at 20-30 at the time, I think. We were running on a dual processor machine on a 6 drive RAID, so we followed the instructions in the InnoDB manual and set thread concurrency to 8. The problems immediately went away.
Haven't tried increasing it now that we're on a G5, a few revisions of the OS and a few revisions of InnoDB newer. Performance seems fine as is.
--Ware Adams
Best regards,
Heikki Innobase Oy InnoDB - transactions, row level locking, and foreign keys for MySQL InnoDB Hot Backup - a hot backup tool for InnoDB which also backs up MyISAM tables http://www.innodb.com/order.php
Order MySQL support from http://www.mysql.com/support/index.html
........................... Hi,
This is a question about optimization of mysql's InnoDB performance ... quoting the doc's
> "The default value is 8. If you have low performance and |SHOW INNODB STATUS| reveals many threads waiting for semaphores, > you may have thread thrashing and should try setting this parameter lower or higher..... The default value is 8. If you have low > performance and |SHOW INNODB STATUS| reveals many threads waiting for semaphores, you may have thread thrashing and > should try setting this parameter lower or higher."
What is a reasonable value for a dual Xeon 2.8Ghz with 6 disks? we are currently running with innodb_thread_concurrency=16. Each DB has 200-400 active php clients, and there appears to be quite a large backup within innodb, based on this. Any suggestions? Or experience with setting this option to 500?
Thanks :)
Devananda Neopets, Inc
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