User-Agent: Microsoft-Entourage/11.2.1.051004
Date: Mon, 09 Jan 2006 13:29:30 -0800
Subject: Re: help tuning queries on large database
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "peter royal" <peter.royal@pobox.com>,
	pgsql-performance@postgresql.org
Message-ID: <BFE815BA.1A2F3%llonergan@greenplum.com>
Thread-Topic: [PERFORM] help tuning queries on large database
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Peter,

On 1/9/06 12:59 PM, "peter royal" <peter.royal@pobox.com> wrote:


> Overall, I got a 50% boost in the overall speed of my test suite by
> using XFS and the 16k read-ahead.

Yes, it all looks pretty good for your config, though it looks like you
might be adapter limited with the Areca - you should have seen a read time
with XFS of about 17 seconds.

OTOH - with RAID5, you are probably about balanced, you should see a read
time of about 19 seconds and instead you'll get your 22 which isn't too big
of a deal.
 
> Thanks for the help!

Sure - no problem!

BTW - I'm running tests right now with the 3Ware 9550SX controllers.  Two of
them on one machine running simultaneously with 16 drives and we're getting
800MB/s sustained read times.  That's a 32GB file read in 40 seconds (!!)

At that rate, we're only about 3x slower than memory access (practically
limited at around 2GB/s even though the system bus peak is 10GB/s). So, the
point is, if you want to get close to your "warm" speed, you need to get
your disk I/O as close to main memory speed as you can.  With parallel I/O
you can do that (see Bizgres MPP for more).

- Luke