Date: Thu, 22 Feb 2007 21:29:20 +0100
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: Vacuum full very slow due to nonremovable dead rows...What makes
	the dead rows non-removable?
Message-ID: <20070222202920.GA1102@uio.no>
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On Thu, Feb 22, 2007 at 12:19:50PM -0800, Barbara Cosentino wrote:
> I have a table that gets many rows inserted, updated and then deleted,
> consistently throughout the day.  At any point in time this table should
> have no more than 50 actual rows and many times a direct select against
> this table produces no rows.  This table also has a VACUUM FULL ANALYZE
> performed against it about very 30 minutes.

You should not usually need VACUUM FULL; doing so all the time will probably
_decrease_ your performance.

> I noticed the vacuum was taking a considerable amount of time for a table
> with a small number of actual rows.  The output of the first vacuum full
> analyze verbose I performed showed that this table had 3,699,704 dead row
> versions that could not be removed.  This number of dead rows that could
> not be released increased with each vacuum full that was performed. The
> output of the last vacuum full is shown below.  

Do you have any long-running transactions going? Those are likely to make
rows nonremovable. Look for idle workers in a transaction.

/* Steinar */
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Homepage: http://www.sesse.net/