Comments on: Should you have your swap file enabled while running MySQL ?

By: Hide-and-SQL » Blog Archive » observation with regard to the “swappiness” problem

Fri, 21 Nov 2008 00:12:42 +0000

[...] folks on Planet MySQL have encountered issues with mysql and linux going into swap (example 1,2,3). None of the easy solutions (sysctl -w swappiness=0, innodb_flush_method [...]

By: Linux Swap Issue « David’s Weblog

Linux Swap Issue « David’s Weblog — Tue, 05 Aug 2008 00:19:12 +0000

[...] Should you have your swap file enabled while running MySQL ? [...]

By: Blogvorstellung: MySQL Performance Blog at NETWAYS Blog

Blogvorstellung: MySQL Performance Blog at NETWAYS Blog — Fri, 27 Jun 2008 11:18:00 +0000

[...] ging es in letzter Zeit um einen Performancevergleich zwischen MySQL Replikation und DRBD, ob man Swap auf Datenbankservern besser deaktivierten sollte oder wie man am besten die MySQL Logs [...]

By: SmugBlog: Don MacAskill » Blog Archive » MySQL and the Linux swap problem

Fri, 02 May 2008 01:25:14 +0000

[...] since Peter over at Percona wrote about MySQL and swap, I’ve been meaning to write this post. But after I saw Dathan Pattishall’s post on the [...]

By: Log Buffer #92: a Carnival of the Vanities for DBAs

Log Buffer #92: a Carnival of the Vanities for DBAs — Fri, 11 Apr 2008 16:44:04 +0000

[...] has another question on his mind: should you have your swap file enabled while running MySQL? He wants to hear your approach to this matter, having himself experienced variable results. Lots of [...]

By: MySQL需要虚拟内存吗？

MySQL需要虚拟内存吗？ — Thu, 10 Apr 2008 06:19:35 +0000

[...] Should you have your swap file enabled while running MySQL ? [...]

By: Clint Byrum

Clint Byrum — Wed, 09 Apr 2008 18:29:25 +0000

Awesome. That worked well, thanks safari. Reboot was not necessary to test the setting btw, just had to run ‘ulimit -l xxxx’, though I rebooted to make sure it stuck. Somebody really should write the same kind of article for MySQL.

Are there any benchmarks published for large_pages? Seems like it would help a lot for a high degree of concurrency given MySQL’s history of memory allocation bottlenecks.

By: safari

safari — Wed, 09 Apr 2008 08:46:55 +0000

Set memlock (max locked memory) for mysql user in /etc/security/limits.conf to allow this user using such large of memory. After doing that and reboot the server, if you still get the error, try to restart mysqld then you can see it works.

You can find more information at http://www.puschitz.com/TuningLinuxForOracle.shtml#UsingVeryLargeMemory.

By: Clint Byrum

Clint Byrum — Wed, 09 Apr 2008 00:15:45 +0000

On our big central DB server, we only have swap enabled because of tmpfs usage for tmpdir. We use a 20G tmpfs partition for tmpdir, and while we generally do have about 20G of RAM available, making tempfiles go quite fast, it also must be used for connection buffers/etc… if the server gets a lot of concurrent connections, I’d rather have it swap out the tempfiles and service the requests, than crash MySQL, or lower max_connections and have to give a ‘max connects reached’ error.

On a somewhat OT note, I see a lot of mention of large_pages here. I’ve spent the last hour trying to make them work on our new server that has 64G RAM… I keep getting these when starting though..(innodb_buffer_pool_size=31G):

InnoDB: HugeTLB: Warning: Failed to allocate 33286012928 bytes. errno 12
InnoDB HugeTLB: Warning: Using conventional memory pool
Warning: Failed to allocate 440401920 bytes from HugeTLB memory. errno 12

/proc/sys/vm/nr_hugepages is 25000 (which is what I set it to at boot time, and equals about 48GB) , page size is 2MB .. /proc/sys/kernel/shmmax is 32GB, shmall is 42GB.

errno 12, btw, is just “cannot allocate memory”

If anyone has experience with large_pages like this, please email me or post here. Thanks!

By: Parvesh

Parvesh — Tue, 08 Apr 2008 17:35:45 +0000

I always prefer to have swap enabled on my boxes and just keep a check on it. I do believe that if swapping (or any other unwanted issue) is happening, the first place one should look is at the application and not the server.

As safari mentioned, large-pages always come handy.