From: Richard Huxton <dev@archonet.com>
To: philippe <philippe@camailia.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Slow query with 'or' clause
Date: Thu, 15 Feb 2007 15:44:33 +0000
Message-ID: <45D47FE1.5010209@archonet.com> (raw)
In-Reply-To: <1171550213.45d470056249c@ssl0.ovh.net>
References: <1171550213.45d470056249c@ssl0.ovh.net>
philippe wrote:
> explain analyse
> select count(*) from client_contact
> left join client_company using(cli_id)
> where (cli_mail = 'xxx@xxx.xx') OR
> (lower(cli_nom) = 'xxxxxx' and zipcode = '10001');
>
> QUERY PLAN
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> Aggregate (cost=37523.98..37523.99 rows=1 width=0) (actual
> time=3871.086..3871.087 rows=1 loops=1)
> -> Merge Left Join (cost=0.00..36719.10 rows=321952 width=0) (actual
> time=3871.058..3871.058 rows=0 loops=1)
This is the root of the problem - it's expecting to match over 320000
rows rather than 0.
I'm guessing there's a lot of correlation between cli_mail and cli_nom
(you're expecting them to match the same clients) but the planner
doesn't know this.
If this is a common query, you could try an index on zipcode - that
might cut down the other side.
However, I have to ask why you're using a left-join? Do you really have
rows in client_contact without a matching cli_id in client_company?
--
Richard Huxton
Archonet Ltd
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-performance@postgresql.org
Cc: dev@archonet.com, philippe@camailia.com
Subject: Re: Slow query with 'or' clause
In-Reply-To: <45D47FE1.5010209@archonet.com>
* 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