To: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Materializing a sequential scan 
In-reply-to: <20051019174544.GA32303@samfundet.no> 
References: <20051019174544.GA32303@samfundet.no>
Comments: In-reply-to "Steinar H. Gunderson" <sgunderson@bigfoot.com>
	message dated "Wed, 19 Oct 2005 19:45:44 +0200"
Date: Thu, 20 Oct 2005 00:37:25 -0400
Message-ID: <4248.1129783045@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
> I'm using PostgreSQL 8.1 beta 3 (packages from Debian experimental), and I
> have a (rather complex) query that seems to take forever -- when the database
> was just installed, it took about 1200ms (which is quite good, considering
> that the 7.4 system this runs on today uses about the same time, but has
> twice as much CPU power and runs sequential scans up to eight times as fast),
> but now I can never even get it to complete. I've tried running it for half
> an hour, but it still doesn't complete, so I'm a bit unsure what's going on.

That mdb_gruppekobling_transitiv_tillukning function looks awfully
grotty ... how many rows does it return, and how long does it take to
run by itself?  How often does its temp table get vacuumed?  A quick
band-aid might be to use TRUNCATE instead of DELETE FROM to clean the
table ... but if I were you I'd try to rewrite the function entirely.

			regards, tom lane