Re: strange performance regression between 7.4 and 8.1

At 10:25 AM 3/6/2007, Alex Deucher wrote:
>On 3/5/07, Guido Neitzer <lists(at)event-s(dot)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...

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.

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.

Best Wishes,
Ron Peacetree