Re: Postgresql Performance on an HP DL385 and

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(at)pervasive(dot)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(at)pervasive(dot)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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