From: A. Kretschmer <andreas.kretschmer@schollglas.com>
To: pgsql-sql@postgresql.org
Subject: Re: many 'OR' in WHERE-condition
Date: Fri, 20 Apr 2007 13:29:30 +0200
Message-ID: <20070420112930.GE15322@a-kretschmer.de> (raw)
In-Reply-To: <46289E10.9060302@archonet.com>
References: <20070420051341.GA15322@a-kretschmer.de>
<46289E10.9060302@archonet.com>
am Fri, dem 20.04.2007, um 12:03:44 +0100 mailte Richard Huxton folgendes:
> A. Kretschmer wrote:
> >in a SELECT with a condition 'WHERE foo IN (1,2,3,4,...)' with a large
> ...
> >But if the list increase the planner choose an seq-scan. The amount of
> >values in the list is about 200 and the table has about 250.000 rows.
> >
> >How can we avoid the seq-scan?
>
> Are you sure you'd want to? What plan have you found to be faster with
> 200 tests?
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
Andreas
--
Andreas Kretschmer
Kontakt: Heynitz: 035242/47150, D1: 0160/7141639 (mehr: -> Header)
GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: andreas.kretschmer@schollglas.com
Subject: Re: many 'OR' in WHERE-condition
In-Reply-To: <20070420112930.GE15322@a-kretschmer.de>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox