From: Tom Lane <tgl@sss.pgh.pa.us>
To: ogjunk-pgjedan@yahoo.com
Cc: pgsql-sql@postgresql.org
Subject: Re: Help with a seq scan on multi-million row table
Date: Wed, 10 May 2006 21:53:49 -0400
Message-ID: <26129.1147312429@sss.pgh.pa.us> (raw)
In-Reply-To: <20060511013410.83818.qmail@web50307.mail.yahoo.com>
References: <20060511013410.83818.qmail@web50307.mail.yahoo.com>
<ogjunk-pgjedan@yahoo.com> writes:
> Aha! set hashjoin=off did the trick.
> -> Index Scan using ix_user_url_tag_user_url_id on user_url_tag userurltag0_ (cost=0.00..157.34 rows=103 width=14) (actual time=1.223..1.281 rows=5 loops=1666)
> Index Cond: (userurltag0_.user_url_id = "outer".id)
This seems to be the problem right here: the estimate of matching rows
is off by a factor of 20, and that inflates the overall cost estimate
for this plan about the same, causing the planner to think the other way
is cheaper.
What does the pg_stats row for user_url_tag.user_url_id contain?
Have you analyzed that table recently?
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, ogjunk-pgjedan@yahoo.com
Subject: Re: Help with a seq scan on multi-million row table
In-Reply-To: <26129.1147312429@sss.pgh.pa.us>
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