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Message-ID: <46F7C9F1.1080805@enterprisedb.com>
Date: Mon, 24 Sep 2007 15:30:09 +0100
From: "Heikki Linnakangas" <heikki@enterprisedb.com>
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To: =?iso-8859-1?Q?G=E1bor_Farkas?= <gabor@nekomancer.net>
Cc: <pgsql-performance@postgresql.org>
Subject: Re: select count(*) performance (vacuum did not help)
References: <46F7C494.1050604@nekomancer.net>
In-Reply-To: <46F7C494.1050604@nekomancer.net>
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Gábor Farkas wrote:
> - this table has a lot of updates and inserts, it works very similarly
> to a session-table for a web-application

Make sure you run VACUUM often enough.

> - there is a cron-job that deletes all the old entries, so it's size is
> rougly between 15000 and 35000 entries (it's run daily, and every day
> deletes around 10000 entries)

Running vacuum after these deletes to immediately reclaim the dead space
would also be a good idea.

> - but in the past, the cron-job was not in place, so the table's size
> grew to around 800000 entries (in around 80 days)

That bloated your table, so that there's still a lot of empty pages in
it. VACUUM FULL should bring it back to a reasonable size. Regular
normal non-FULL VACUUMs should keep it in shape after that.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com