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  • 1.  Clearing File System Cache on AIX

    Posted Thu November 05, 2009 04:22 PM

    Originally posted by: SystemAdmin


    I have a relatively unique situation where a group of testers that are accessing various files for testing software are running into an issue where our AIX servers are being too efficient. They are running tests that reference files, after the test are done they will make modifications to the application parameters and re-test, the problem is that the files are being read from the cache and returning very good performance numbers, as one would expect/desire....except for my testers. They want it to run like the server has never seen the files before.
    Is there a way to clear the file system cache on an AIX server short of rebooting it? On a Linux server I would just use drop_cache, but I haven't been able to find much in regard to a comparable tool on AIX. Anyone ran into this kind of a need before? Thank you.


  • 2.  Re: Clearing File System Cache on AIX

    Posted Thu November 05, 2009 08:22 PM

    Originally posted by: dukessd


    AFAIK no.
    reboot
    Sorry.


  • 3.  Re: Clearing File System Cache on AIX

    Posted Fri November 06, 2009 01:28 AM

    Originally posted by: The_Doctor


    Haven't tried this myself, but have a look at the mount command.

    mount -p

    or

    mount -o rbrw

    looks like it might do what you want.


  • 4.  Re: Clearing File System Cache on AIX

    Posted Fri November 06, 2009 11:23 AM

    Originally posted by: SystemAdmin


    Thank you, I completely blanked on looking at the file systems themselves. These options probably will work, but the testers would like to take advantage of the caching while they are running the jobs on a first run basis...so while this would work it's not ideal because it would impair the performance at all times.


  • 5.  Re: Clearing File System Cache on AIX

    Posted Fri November 06, 2009 04:07 AM

    Originally posted by: j.gann


    more options: umount the fs between tests
    or use direct io (dio mount parameter)


  • 6.  Re: Clearing File System Cache on AIX

    Posted Fri November 06, 2009 11:24 AM

    Originally posted by: SystemAdmin


    This did exactly what we were looking for...unmount and remount the file systems that data was on and the cache dumps....thank you, this will save me lots of time in rebooting!


  • 7.  Re: Clearing File System Cache on AIX

    Posted Fri November 06, 2009 07:43 PM

    Originally posted by: dukessd


    Nice one, of course an unmount would dump the cache, now why wasn't that obvious at 01:30 after so much beer....
    Well done j.gann, no wonder you are a VC.


  • 8.  Re: Clearing File System Cache on AIX

    Posted Sat November 07, 2009 01:43 AM

    Originally posted by: Kosala


    The way I see direct IO (dio) is a good option or you can try playing with minfree, maxfree, minperm and maxperm.

    http://publib.boulder.ibm.com/infocenter/tsminfo/v6/index.jsp?topic=/com.ibm.itsm.perf.doc/c_aix_vmo_ioo.html
    http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.cmds/doc/aixcmds6/vmo.htm


  • 9.  Re: Clearing File System Cache on AIX

    Posted Tue November 10, 2009 02:14 PM

    Originally posted by: SystemAdmin


    Just following up on the dio option. In our situation where we are thrashing through lots of records\and referencing data on the file system in question, losing the caching during the run was indeed a huge hit on the performance. A basic test that took two hours to run with the fs caching was only 20% after three hours with the file system mounted in dio mode(we pulled the plug there so I don't have a true end to end test result). I wasn't expecting the impact to be that dramatic, but it was. We'll stick with yanking the rug out from under....of course now I'll need to script something that will enable the engineers to do it at will via sudo....