From: Gregory Stark <stark@enterprisedb.com>
To: Andrus <kobruleht2@hot.ee>
Cc: pgsql-performance@postgresql.org
Subject: Re: seq scan over 3.3 million rows instead of single key index access
Date: Sat, 22 Nov 2008 23:03:50 +0000
Message-ID: <87k5avz7l5.fsf@oxford.xeocode.com> (raw)
In-Reply-To: <gg9pg7$1edv$2@news.hub.org>
References: <gg9pg7$1edv$2@news.hub.org>
"Andrus" <kobruleht2@hot.ee> writes:
> There are indexes on rid(dokumnr) and dok(dokumnr) and dokumnr is int.
> Instead of using single key index, 8.1.4 scans over whole rid table.
> Sometimes idtelluued can contain more than single row so replacing join with
> equality is not possible.
>
> How to fix ?
Firstly the current 8.1 release is 8.1.15. Any of the bugs fixed in those 11
releases might be related to this.
Secondly:
> CREATE TEMP TABLE idtellUued(dokumnr INT) ON COMMIT DROP;
> INSERT INTO idtellUued VALUES(1249228);
> explain analyze select 1
> from dok JOIN rid USING(dokumnr)
> JOIN idtellUued USING(dokumnr)
>
> " -> Seq Scan on idtelluued (cost=0.00..31.40 rows=2140 width=4)
> (actual time=0.006..0.011 rows=1 loops=1)"
The planner thinks there are 2,140 rows in that temporary table so I don't
believe this is from the example posted. I would suggest running ANALYZE
idtellUued at some point before the problematic query.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
Ask me about EnterpriseDB's Slony Replication support!
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To: pgsql-performance@postgresql.org
Cc: stark@enterprisedb.com, kobruleht2@hot.ee
Subject: Re: seq scan over 3.3 million rows instead of single key index access
In-Reply-To: <87k5avz7l5.fsf@oxford.xeocode.com>
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