From: Richard Huxton <dev@archonet.com>
To: A. Kretschmer <andreas.kretschmer@schollglas.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: many 'OR' in WHERE-condition
Date: Fri, 20 Apr 2007 12:59:01 +0100
Message-ID: <4628AB05.6000400@archonet.com> (raw)
In-Reply-To: <20070420112930.GE15322@a-kretschmer.de>
References: <20070420051341.GA15322@a-kretschmer.de>
<46289E10.9060302@archonet.com>
<20070420112930.GE15322@a-kretschmer.de>
A. Kretschmer wrote:
>
> It's not my problem - i found it in a forum (german)
> http://pg-forum.de/showthread.php?t=1332
>
> If the list contains up to 195 entrys -> up to 195 bitmap index scans
> and BitmapOr -> 7.839ms
>
> If the list contains 196 entrys -> seq-scan -> 5591.567ms
It looks like it's getting the row estimate badly wrong.
"Seq Scan on t_datasets_searchindices_rel (cost=0.00..129053.50
rows=159277 width=4) (actual time=0.213..5590.435 rows=325 loops=1)
Probably worth increasing the statistics estimate for that column (ALTER
TABLE ... ALTER COLUMN ... SET STATISTICS=N)
It also looks like it's getting the cost estimates badly wrong. Probably
worth asking the original poster to read the tuning guide.
--
Richard Huxton
Archonet Ltd
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To: pgsql-sql@postgresql.org
Cc: dev@archonet.com, andreas.kretschmer@schollglas.com
Subject: Re: many 'OR' in WHERE-condition
In-Reply-To: <4628AB05.6000400@archonet.com>
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