From: Jeremy Harris <jgh@wizmail.org>
To: Pgsql-Performance <pgsql-performance@postgresql.org>
Subject: Re: sequence scan problem
Date: Sun, 29 Jun 2008 23:10:40 +0100
Message-ID: <48680860.2000300@wizmail.org> (raw)
In-Reply-To: <48680418.7030708@gmail.com>
References: <48680418.7030708@gmail.com>
John Beaver wrote:
> I'm having a strange problem with a query. The query is fairly simple,
> with a few constants and two joins. All relevant columns should be
> indexed, and I'm pretty sure there aren't any type conversion issues.
> But the query plan includes a fairly heavy seq scan. The only possible
> complication is that the tables involved are fairly large - hundreds of
> millions of rows each.
>
> Can anyone explain this? There should only ever be a maximum of about 50
> rows returned when the query is executed.
You didn't say when you last vacuumed?
If there should only be 50 rows returned then the estimates from the
planner are way out.
If that doesn't help, we'll need version info, and (if you can afford
the time) an "explain analyze"
Cheers,
Jeremy
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: jgh@wizmail.org
Subject: Re: sequence scan problem
In-Reply-To: <48680860.2000300@wizmail.org>
* 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