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. :-/
--
Jeff Frost, Owner <jeff@xxxxxxxxxxxxxxxxxxxxxx>
Frost Consulting, LLC http://www.frostconsultingllc.com/
Phone: 650-780-7908 FAX: 650-649-1954
