Re: Perfomance Tuning

Uh, the ext2 developers say it isn't 100% reliable --- at least that is
that was told.  I don't know any personally, but I mentioned it while I
was visiting Red Hat, and they didn't refute it.

Now, the failure window might be quite small, but I have seen it happen
myself, and have heard it from others.

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Reece Hart wrote:
> On Mon, 2003-08-11 at 15:16, Bruce Momjian wrote:
>
> > That _would_ work if ext2 was a reliable file system --- it is not.
>
>
> Bruce-
>
> I'd like to know your evidence for this. I'm not refuting it, but I'm a
> >7 year linux user (including several clusters, all of which have run
> ext2 or ext3) and keep a fairly close ear to kernel newsgroups,
> announcements, and changelogs. I am aware that there have very
> occasionally been corruption problems, but my understanding is that
> these are fixed (and quickly). In any case, I'd say that your assertion
> is not widely known and I'd appreciate some data or references.
>
> As for PostgreSQL on ext2 and ext3, I recently switched from ext3 to
> ext2 (Stephen Tweedy was insightful to facilitate this backward
> compatibility). I did this because I had a 45M row update on one table
> that was taking inordinate time (killed after 10 hours), even though
> creating the database from backup takes ~4 hours including indexing (see
> pgsql-perform post on 2003/07/22). CPU usage was ~2% on an otherwise
> unloaded, fast, SCSI160 machine. vmstat io suggested that PostgreSQL was
> writing something on the order of 100x as many blocks as being read. My
> untested interpretation was that the update bookkeeping as well as data
> update were all getting journalled, the journal space would fill, get
> sync'd, then repeat. In effect, all blocks were being written TWICE just
> for the journalling, never mind the overhead for PostgreSQL
> transactions. This emphasizes that journals probably work best with
> short burst writes and syncing during lulls rather than sustained
> writes.
>
> I ended up solving the update issue without really updating, so ext2
> timings aren't known. So, you may want to test this yourself if you're
> concerned.
>
> -Reece
>
>
> --
> Reece Hart, Ph.D.                       rkh@gene.com, http://www.gene.com/
> Genentech, Inc.                         650/225-6133 (voice), -5389 (fax)
> Bioinformatics and Protein Engineering
> 1 DNA Way, MS-93                        http://www.in-machina.com/~reece/
> South San Francisco, CA  94080-4990     reece@in-machina.com, GPG: 0x25EC91A0

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