Re: Tuning for PostGreSQL Database

From: Jim C. Nasby (jim_at_nasby.net)
Date: 07/21/03

  • Next message: Sean Chittenden: "Re: Tuning for PostGreSQL Database" 
    Date: Mon, 21 Jul 2003 14:45:19 -0500
To: Sean Chittenden <sean@chittenden.org>

    On Mon, Jul 21, 2003 at 12:26:45PM -0700, Sean Chittenden wrote:
    > > > 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.
     
    So are you saying that softupdates on whatever partition contains the
    database transaction logs is dangerous?

    Luckily, the metadata for these files is changed very infrequently
    (normally), so this shouldn't prove to be much of a performance impact. 

    -- 
Jim C. Nasby, Database Consultant                  jim@nasby.net
Member: Triangle Fraternity, Sports Car Club of America
Give your computer some brain candy! www.distributed.net Team #1828
Windows: "Where do you want to go today?"
Linux: "Where do you want to go tomorrow?"
FreeBSD: "Are you guys coming, or what?"
_______________________________________________
freebsd-performance@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-performance
To unsubscribe, send any mail to "freebsd-performance-unsubscribe@freebsd.org"
  • Next message: Sean Chittenden: "Re: Tuning for PostGreSQL Database"

    Relevant Pages

    • Re: Tuning for PostGreSQL Database
      ... Softupdates is just a better async. ... If you have a file system (such as the root file ...
      (freebsd-performance)
    • Re: Tuning for PostGreSQL Database
      ... >> determining whether to use it on a file system. ... >> softupdates guarantees file system consistency in the case of ... > the database transaction logs is dangerous? ... volatle backed buffer increases the danger of data loss. ...
      (freebsd-performance)
    • Re: Disabling background fsck; disabling softupdates; defaulting to "fsck -y"
      ... I have encountered problems where key system services ... start reading garbage from the file system before fsck completes. ... corruption, should I turn off softupdates? ...
      (comp.unix.bsd.freebsd.misc)
    • Re: UNEXPECTED SOFTUPDATES INCONSISTENCY
      ... > in case of crash, but thousands of lost files tell a different story. ... Or should i disable softupdates for important data? ...
      (freebsd-questions)