On Tue, Jan 09, 2007 at 09:10:51AM -0800, Jeff Frost wrote:
> On Tue, 9 Jan 2007, Jim C. Nasby wrote:
>
> >On Thu, Dec 28, 2006 at 02:15:31PM -0800, Jeff Frost wrote:
> >>When benchmarking various options for a new PG server at one of my
> >>clients,
> >>I tried ext2 and ext3 (data=writeback) for the WAL and it appeared to be
> >>fastest to have ext2 for the WAL. The winning time was 157m46.713s for
> >>ext2, 159m47.098s for combined ext3 data/xlog and 158m25.822s for ext3
> >>data=writeback. This was on an 8x150GB Raptor RAID10 on an Areca 1130 w/
> >>1GB BBU cache. This config benched out faster than a 6disk RAID10 + 2
> >>disk
> >>RAID1 for those of you who have been wondering if the BBU write back cache
> >>mitigates the need for separate WAL (at least on this workload). Those
> >>are
> >>the fastest times for each config, but ext2 WAL was always faster than the
> >>other two options. I didn't test any other filesystems in this go around.
> >
> >Uh, if I'm reading this correctly, you're saying that WAL on a separate
> >ext2 vs. one big ext3 with data=writeback saved ~39 seconds out of
> >~158.5 minutes, or 0.4%? Is that even above the noise for your
> >measurements? I suspect the phase of the moon might play a bigger role
> >;P
>
> That's what I thought too...cept I ran it 20 times and ext2 won by that
> margin every time, so it was quite repeatable. :-/
Even so, you've got to really be hunting for performance to go through
the hassle of different filesystems just to gain 0.4%... :)
--
Jim Nasby jim@nasby.net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)