Re: strange performance regression between 7.4 and 8.1

On 3/6/07, Ron <rjpeace@earthlink.net> wrote:
> At 10:25 AM 3/6/2007, Alex Deucher wrote:
> >On 3/5/07, Guido Neitzer <lists@event-s.net> wrote:
> >>On 05.03.2007, at 19:56, Alex Deucher wrote:
> >>
> >> > Yes, I started setting that up this afternoon.  I'm going to test that
> >> > tomorrow and post the results.
> >>
> >>Good - that may or may not give some insight in the actual
> >>bottleneck. You never know but it seems to be one of the easiest to
> >>find out ...
> >
> >Well, the SAN appears to be the limiting factor.  I set up the DB on
> >the local scsi discs (software RAID 1) and performance is excellent
> >(better than the old server).  Thanks for everyone's help.
> >
> >Alex
>
> What kind of SAN is it and how many + what kind of HDs are in it?
> Assuming the answers are reasonable...
>

It's a Hitachi WMS/Tagmastore.  105 hitachi SATA drives; 4 Gbps FC.

> Profile the table IO pattern your workload generates and start
> allocating RAID sets to tables or groups of tables based on IO pattern.
>
> For any table or group of tables that has a significant level of
> write IO, say >= ~25% of the IO mix, try RAID 5 or 6 first, but be
> prepared to go RAID 10 if performance is not acceptable.
>

Right now it's designed for max capacity: big RAID 5 groups.  I expect
I'll probably need RAID 10 for decent performance.

> Don't believe any of the standard "lore" regarding what tables to put
> where or what tables to give dedicated spindles to.
> Profile, benchmark, and only then start allocating dedicated resources.
> For instance, I've seen situations where putting pg_xlog on its own
> spindles was !not! the right thing to do.
>

Right.  Thanks for the advice.  I'll post my results when I get around
to testing some new SAN configurations.

Alex