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uncache!

this is source code for a tiny program I just wrote that traverses specified directories and removes them from file system cache.

There are few use cases for it. One is for all these people who benchmark stuff and want selective OS cache purges, another is for those who run high performance databases. Remember the O_DIRECT serialization everywhere? Well, XFS does direct I/O in parallel, unless there are cached pages (and they can happen because of any random outside-of-database activity, like ‘file’ command). Once you ‘uncache’ the files, XFS will be very much parallel again \o/ \o/

This entry was posted on Friday, June 26th, 2009 at 13:40 and is filed under mysql. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

5 Responses to “uncache!”

  1. Partha Dutta says:
    June 26, 2009 at 18:11

    In new versions of linux, (and RHEL 4u6 and higher), you can also remove entries from the file system cache using /proc/sys/vm/drop_caches

  2. Domas Mituzas says:
    June 26, 2009 at 18:42

    Partha, I know, but not individually.. ;-)

  3. Uncaching bits in filesystem cache says:
    July 9, 2009 at 20:17

    [...] Domas makes something more useful than I bet most would think: http://mituzas.lt/2009/06/26/uncache/ [...]

  4. Remova arquivos do cache de disco | George Guimarães on Tech says:
    July 14, 2009 at 03:06

    [...] Porém às vezes o cache do seu file system atrapalha. Em procedimentos de benchmark (principalmente de DB), no qual você quer analisar apenas uma das camadas de software, o ideal é desativar o cache. Você pode fazer isso setando algumas opções no /proc, desativando o cache pelo /etc/fstab ou melhor ainda: use o uncache! [...]

  5. links for 2009-07-14 « Dan Creswell’s Linkblog says:
    July 14, 2009 at 14:04

    [...] uncache! « domas mituzas: vaporware, inc. There are few use cases for it. One is for all these people who benchmark stuff and want selective OS cache purges, another is for those who run high performance databases. Remember the O_DIRECT serialization everywhere? Well, XFS does direct I/O in parallel, unless there are cached pages (and they can happen because of any random outside-of-database activity, like ‘file’ command). Once you ‘uncache’ the files, XFS will be very much parallel again o/ o/ (tags: linux filesystem cache management) [...]