Comments on: Linux IO Schedulers and MySQL http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/ Everything about MySQL Performance Wed, 19 Nov 2008 23:36:14 +0000 http://wordpress.org/?v=2.5.1 By: veridicus http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41826 veridicus Fri, 02 Feb 2007 16:08:46 +0000 http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41826 Very interesting article. Thanks for pointing us to it! Very interesting article. Thanks for pointing us to it!

]]> By: peter http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41814 peter Fri, 02 Feb 2007 14:22:03 +0000 http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41814 Yes, I've seen that paper. The problem is it is rather old... the IO schedulers are changing quickly as you can read in original article. Yeah it is a pity CentOS/RHEL only allow scheduler to be changed on boot. I think it is just because it is based on older kernel. version 5 hopefully will not have this problem. I guess CFQ vs Deadline depends on applications I've seen mixed results. Yes, I’ve seen that paper. The problem is it is rather old… the IO schedulers are changing quickly as you can read in original article.

Yeah it is a pity CentOS/RHEL only allow scheduler to be changed on boot. I think it is just because it is based on older kernel. version 5 hopefully will not have this problem.

I guess CFQ vs Deadline depends on applications I’ve seen mixed results.

]]> By: Jason Frisvold http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41813 Jason Frisvold Fri, 02 Feb 2007 14:16:25 +0000 http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41813 The comment system happily ate part of the filename I posted above.. it should be : /sys/block/DEVICENAME/queue/scheduler And example would be something like : /sys/block/hda/queue/scheduler The comment system happily ate part of the filename I posted above.. it should be :

/sys/block/DEVICENAME/queue/scheduler

And example would be something like :

/sys/block/hda/queue/scheduler

]]> By: Jason Frisvold http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41812 Jason Frisvold Fri, 02 Feb 2007 14:15:01 +0000 http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-41812 I did some brief research on the four available schedulers and came across this page : http://www.redhat.com/magazine/008jun05/features/schedulers/ Redhat also claims that the CFQ scheduler is the best overall for database applications. But it also looks like deadline may be an option as well. Am I correct in stating that the deadline scheduler offers better long-term performance compared to CFQ? Or am I misreading that graph? At any rate, the scheduler can be selected on the fly for many distributions by changing the value of /sys/block//queue/scheduler to one of the four scheduler names. In Fedora, if you cat this file it will display the four available schedulers and the current one is listed in brackets. Redhat Enterprise, and thus CentOS, only allow scheduler changes on bootup. This stems from an older 2.6 kernel being used. Fun stuff. Worth running some benchmarks on... I did some brief research on the four available schedulers and came across this page :

http://www.redhat.com/magazine/008jun05/features/schedulers/

Redhat also claims that the CFQ scheduler is the best overall for database applications. But it also looks like deadline may be an option as well. Am I correct in stating that the deadline scheduler offers better long-term performance compared to CFQ? Or am I misreading that graph?

At any rate, the scheduler can be selected on the fly for many distributions by changing the value of /sys/block//queue/scheduler to one of the four scheduler names. In Fedora, if you cat this file it will display the four available schedulers and the current one is listed in brackets.

Redhat Enterprise, and thus CentOS, only allow scheduler changes on bootup. This stems from an older 2.6 kernel being used.

Fun stuff. Worth running some benchmarks on…

]]> By: peter http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-40485 peter Wed, 31 Jan 2007 14:38:16 +0000 http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-40485 That is good to hear each threads gets its own queue. I remember in 2.4 times there were compatibility issues with threads and read-ahead which was tracked per process not per thread. Regarding ionice it is tough to use with database as there can be priority inversion due to lock held by the thread etc. What would be great to see implemented is per request priorities so log flushes for example would get high priority while background dirty pages flush low priority. That is good to hear each threads gets its own queue. I remember in 2.4 times there were compatibility issues with threads and read-ahead which was tracked per process not per thread.

Regarding ionice it is tough to use with database as there can be priority inversion due to lock held by the thread etc.

What would be great to see implemented is per request priorities so log flushes for example would get high priority while background dirty pages flush low priority.

]]> By: n http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-40450 n Wed, 31 Jan 2007 11:37:07 +0000 http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-40450 Each thread gets its own queue. You can also do ionice per thread. However it doesn't quite work for AIO which gets submitted from other threads. I think it's pretty important to always measure latencies too, not just aggregate throughput Each thread gets its own queue. You can also do ionice per thread.

However it doesn’t quite work for AIO which gets submitted from other threads.

I think it’s pretty important to always measure latencies too, not just aggregate throughput

]]> By: UNIX-WORLD NEWS : Linux IO schedulers and MySQL http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-39878 UNIX-WORLD NEWS : Linux IO schedulers and MySQL Tue, 30 Jan 2007 19:00:52 +0000 http://www.mysqlperformanceblog.com/2007/01/30/linux-io-schedulers-and-mysql/#comment-39878 [...] Read more [...] [...] Read more [...]

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