Jim,
I have to say Michael is onto something here to my surprise. I partitioned the RAID10 on the SmartArray 642 adapter into two parts, PGDATA formatted with XFS and pg_xlog as ext2. Performance jumped up to median of 98 TPS. I could reproduce the similar result with the LSI MegaRAID 2X adapter as well as with my own 4-disc drive array.
The problem lies with the HP SmartArray 6i adapter and/or the internal SCSI discs. Putting the pg_xlog on it kills the performance.
Steve
On 8/14/06, Jim C. Nasby <jnasby@pervasive.com> wrote: On Thu, Aug 10, 2006 at 07:09:38AM -0400, Michael Stone wrote:
> On Wed, Aug 09, 2006 at 08:29:13PM -0700, Steve Poe wrote:
> >I tried as you suggested and my performance dropped by 50%. I went from
> >a 32 TPS to 16. Oh well.
>
> If you put data & xlog on the same array, put them on seperate
> partitions, probably formatted differently (ext2 on xlog).
Got any data to back that up?
The problem with seperate partitions is that it means more head movement
for the drives. If it's all one partition the pg_xlog data will tend to
be interspersed with the heap data, meaning less need for head
repositioning.
Of course, if ext2 provided enough of a speed improvement over ext3 with
data=writeback then it's possible that this would be a win, though if
the controller is good enough to make putting pg_xlog on the same array
as $PGDATA a win, I suspect it would make up for most filesystem
performance issues associated with pg_xlog as well.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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