Re: Tuning for PostGreSQL Database

From: Sean Chittenden (sean_at_chittenden.org)
Date: 07/21/03

  • Next message: Jim C. Nasby: "Re: Tuning for PostGreSQL Database" 
    Date: Mon, 21 Jul 2003 12:26:45 -0700
To: Jason Stone <freebsd-performance@dfmm.org>

    > > Softupdates on, async off. Softupdates is just a better async.
    >
    > postgresql fsync's all its files before returning from a commit in
    > order to ensure durability, right? Does softupdates interfere with
    > the functioning of sync(2)/fsync(2)?

    It can, yes, but that's the risk of soft updates. From tuning(7):

         Softupdates drastically improves meta-data performance, mainly
         file creation and deletion. We recommend enabling softupdates on
         most file systems; however, there are two limitations to
         softupdates that you should be aware of when determining whether
         to use it on a file system. First, softupdates guarantees file
         system consistency in the case of a crash but could very easily
         be several seconds (even a minute!) behind on pending write to
         the physical disk. If you crash you may lose more work than
         otherwise. Secondly, softupdates delays the freeing of file
         system blocks. If you have a file system (such as the root file
         system) which is close to full, doing a major update of it,
         e.g. ``make installworld'', can run it out of space and cause the
         update to fail. For this reason, softupdates will not be enabled
         on the root file system during a typical install.

    > > > I would recommend 4.8 over 5.1. Especially if you intend this
    > > > to be a production server. 5.1 is not ready for public
    > > > consumption.
    > >
    > > Public consumption, yes. Production consumption, no.
    >
    > I recently decided to take up the issue of migrating towards 5.1 at
    > my company. The way I dealt with it was to publish all of my
    > services to 5.1 boxes and run regression tests. For me, 5.1
    > provided adequate performance, and since 5.1 is on the branch where
    > all new dev work is going on and 4.x is going to be end-of-lifed in
    > the not-too-distant future, I decided to go with 5.1.
    >
    > Personally, I would only go with 4.8 if testing showed 5.1 to be
    > inadequate for your particular situation with your particular apps,
    > hardware, load, etc. But you can only tell that by testing.

    Glad to hear that 5.1 is getting used in the work place. Were there
    any places where your testing showed huge gaps in performance? -sc 

    -- 
Sean Chittenden
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  • Next message: Jim C. Nasby: "Re: Tuning for PostGreSQL Database"

    Relevant Pages

    • Re: Tuning for PostGreSQL Database
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      ... Softupdates is just a better async. ... > postgresql fsync's all its files before returning from a commit in order ...
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