From: Stephen Frost <sfrost@snowman.net>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jay Greenfield <jag@timberline.ca>
Cc: pgsql-performance@postgresql.org
Subject: Re: Postgres slower than MS ACCESS
Date: Tue, 14 Feb 2006 15:55:10 -0500
Message-ID: <20060214205510.GJ4474@ns.snowman.net> (raw)
In-Reply-To: <22347.1139949764@sss.pgh.pa.us>
References: <200602141551.k1EFpN6F020512@timberline.ca>
<20060214172022.GC4474@ns.snowman.net>
<22347.1139949764@sss.pgh.pa.us>
* Tom Lane (tgl@sss.pgh.pa.us) wrote:
> Stephen Frost <sfrost@snowman.net> writes:
> > While it's true that Access almost certainly takes some shortcuts, 24
> > minutes for an update across 1.2 millon rows seems an awefully long time
> > for Postgres.
>
> I did some experiments along this line with a trivial table (2 integer
> columns) of 1.28M rows. I used CVS tip with all parameters at defaults.
> With no indexes, an UPDATE took about 50 seconds. With one index, it
> took 628 seconds. It's not hard to believe you could get to Jay's
> figures with multiple indexes.
With multiple indexes, you might want to drop them and recreate them
when you're updating an entire table.
> Looking in the postmaster log, I see I was getting checkpoints every few
> seconds. Increasing checkpoint_segments to 30 (a factor of 10) brought
> it down to 355 seconds, and then increasing shared_buffers to 20000
> brought it down to 165 sec. Separating WAL and data onto different
> disks would have helped too, no doubt, but I'm too lazy to try it.
Sure, this was kind of my point, we need more information about the
database if we're going to have much of a chance of improving the
results he's seeing. 165 seconds is certainly a great deal better than
24 minutes. :)
Thanks,
Stephen
Attachments:
signature.asc (application/pgp-signature, 188B) download
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: sfrost@snowman.net, tgl@sss.pgh.pa.us, jag@timberline.ca
Subject: Re: Postgres slower than MS ACCESS
In-Reply-To: <20060214205510.GJ4474@ns.snowman.net>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox