From: Tom Lane <tgl@sss.pgh.pa.us>
To: Glenn Sullivan <glenn.sullivan@varianinc.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Performance of ORDER BY
Date: Tue, 05 Dec 2006 13:02:06 -0500
Message-ID: <7090.1165341726@sss.pgh.pa.us> (raw)
In-Reply-To: <4575A863.6040504@varianinc.com>
References: <4575A863.6040504@varianinc.com>
Glenn Sullivan <glenn.sullivan@varianinc.com> writes:
> I am wanting some ideas about improving the performance of ORDER BY in
> our use. I have a DB on the order of 500,000 rows and 50 columns.
> The results are always sorted with ORDER BY. Sometimes, the users end up
> with a search that matches most of the rows. In that case, I have a
> LIMIT 5000 to keep the returned results under control. However, the
> sorting seems to take 10-60 sec. If I do the same search without the
> ORDER BY, it takes about a second.
Does the ORDER BY match an index? If so, is it using the index?
(See EXPLAIN.)
> I am currently on version 8.0.1 on Windows XP using a Dell Optiplex 280
> with 1Gb of ram. I have set sort_mem=100000 set.
In 8.0 that might be counterproductively high --- we have seen cases
where more sort_mem = slower with the older sorting code. I concur
with Luke's advice that you should update to 8.2 (not 8.1) to get the
improved sorting code.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, glenn.sullivan@varianinc.com
Subject: Re: Performance of ORDER BY
In-Reply-To: <7090.1165341726@sss.pgh.pa.us>
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