Comments on: Innodb usability and ease of use. http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/ Everything about MySQL Performance Tue, 02 Dec 2008 20:02:21 +0000 http://wordpress.org/?v=2.5.1 By: Alexander Kjäll http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174987 Alexander Kjäll Fri, 05 Oct 2007 07:27:15 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174987 Kevin Thanks you for clearing that up, it was a good read. Kevin

Thanks you for clearing that up, it was a good read.

]]> By: Antony Curtis http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174859 Antony Curtis Thu, 04 Oct 2007 19:26:39 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174859 The plug-in system available in MySQL 5.1+ permits the declaration of system variables as an ENUM which would easily allow defining variables, such as innodb_flush_logs_at_trx_commit, in a more human friendly way instead of just a number. The plug-in system available in MySQL 5.1+ permits the declaration of system variables as an ENUM which would easily allow defining variables, such as innodb_flush_logs_at_trx_commit, in a more human friendly way instead of just a number.

]]> By: peter http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174777 peter Thu, 04 Oct 2007 10:12:35 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174777 Kevin, Alexander Indeed - O_DIRECT removes IO pressure and so can reduce swapping. But even if your OS VM is smart enough to keep cache size in control there is still the reason to use it, and you're actually stating it. With databases you're indeed sure you will not ever read the same block again - because it is in database buffer pool cache, which is typically larger than OS cache and so it will be most likely first removed from OS cache. Not to mention you likely want to keep your OS cache for things which really need it - like MyISAM tables, sort files etc. Kevin, Alexander

Indeed - O_DIRECT removes IO pressure and so can reduce swapping. But even if your OS VM is smart enough to keep cache size in control there is still the reason to use it, and you’re actually stating it.

With databases you’re indeed sure you will not ever read the same block again - because it is in database buffer pool cache, which is typically larger than OS cache and so it will be most likely first removed from OS cache.

Not to mention you likely want to keep your OS cache for things which really need it - like MyISAM tables, sort files etc.

]]> By: Kevin Burton http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174765 Kevin Burton Thu, 04 Oct 2007 08:37:37 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174765 Alexander, O_DIRECT can provide a huge performance boost since it can trick linux to NOT move the buffer pool into the page file. Here's my recent battle with innodb+linux http://feedblog.org/2007/09/29/using-o_direct-on-linux-and-innodb-to-fix-swap-insanity/ Alexander,

O_DIRECT can provide a huge performance boost since it can trick linux to NOT move the buffer pool into the page file.

Here’s my recent battle with innodb+linux

http://feedblog.org/2007/09/29/using-o_direct-on-linux-and-innodb-to-fix-swap-insanity/

]]> By: Alexander Kjäll http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174764 Alexander Kjäll Thu, 04 Oct 2007 08:19:29 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174764 As far as i have understood it O_DIRECT makes linux not cache the data read from disk, this is a very small performance improvement and only holds true if you either don't have any free memory to cache it in, or are sure you doesn't read it again. Here is an article with Linus Torvalds thoughts on O_DIRECT: http://kerneltrap.org/node/7563 As far as i have understood it O_DIRECT makes linux not cache the data read from disk, this is a very small performance improvement and only holds true if you either don’t have any free memory to cache it in, or are sure you doesn’t read it again.

Here is an article with Linus Torvalds thoughts on O_DIRECT:

http://kerneltrap.org/node/7563

]]> By: Kevin Burton http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174642 Kevin Burton Wed, 03 Oct 2007 19:57:51 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174642 Peter. Good point. So memlock + O_DIRECT seem to be required on Linux if you want to use all your memory and not page. I still have to track down whether this is a bug in 2.6.18 or whether this is expected behavior. Kevin Peter. Good point.

So memlock + O_DIRECT seem to be required on Linux if you want to use all your memory and not page.

I still have to track down whether this is a bug in 2.6.18 or whether this is expected behavior.

Kevin

]]> By: peter http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174547 peter Wed, 03 Oct 2007 10:15:00 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174547 Indeed. O_DIRECT can't be used with Log (on Linux) because it requires aligned IO while log can get writes of various sizes/alignment. Indeed. O_DIRECT can’t be used with Log (on Linux) because it requires aligned IO while log can get writes of various sizes/alignment.

]]> By: Jay Janssen http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174075 Jay Janssen Mon, 01 Oct 2007 17:00:19 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-174075 O_DIRECT doesn't seem to affect the trx log, it applies to how inno opens the data files. O_DIRECT doesn’t seem to affect the trx log, it applies to how inno opens the data files.

]]> By: Kevin Burton http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-173460 Kevin Burton Sat, 29 Sep 2007 04:52:22 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-173460 Hm... what's the downside of using O_DIRECT wrt the write ahead log? We're considering the switch so that innodb doesn't have to worry about the kernel pushing the buffer pool into the page file. Hm… what’s the downside of using O_DIRECT wrt the write ahead log?

We’re considering the switch so that innodb doesn’t have to worry about the kernel pushing the buffer pool into the page file.

]]> By: peter http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-173321 peter Fri, 28 Sep 2007 17:51:58 +0000 http://www.mysqlperformanceblog.com/2007/09/28/innodb-usability-and-ease-of-use/#comment-173321 Jay, I knew something would point that out :) It is simple in the sense of settings which are more or less self descriptive. The logic behind it can be not so simple, you're right. Indeed setting logs and data flush method separately would be better especially as even allowed modes differ between OS. For example O_DIRECT on Linux requires buffer alignment while on Solaris it is not required and so it should be possible to use it for logs as well. Jay,

I knew something would point that out :)

It is simple in the sense of settings which are more or less self descriptive. The logic behind it can be not so simple, you’re right.

Indeed setting logs and data flush method separately would be better especially as even allowed modes differ between OS. For example O_DIRECT on Linux requires buffer alignment while on Solaris it is not required and so it should be possible to use it for logs as well.

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