Date: Thu, 25 Jan 2007 09:54:24 -0600
From: "Jim C. Nasby" <jim@nasby.net>
To: Tomas Vondra <tv@fuzzy.cz>
Cc: pgsql-performance@postgresql.org
Subject: Re: how to plan for vacuum?
Message-ID: <20070125155424.GG64372@nasby.net>
References: <45B6F0A8.1050705@oss.ntt.co.jp>
	<20070125033917.GD64372@nasby.net> <45B8602E.7000606@fuzzy.cz>
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Please cc the list so others can reply as well...

On Thu, Jan 25, 2007 at 08:45:50AM +0100, Tomas Vondra wrote:
> > On Wed, Jan 24, 2007 at 02:37:44PM +0900, Galy Lee wrote:
> >> 1.  How do we know if autovacuum is enough for my application, or should
> >>     I setup a vacuum manually from cron for my application?
> > 
> > Generally I trust autovac unless there's some tables where it's critical
> > that they be vacuumed frequently, such as a queue table or a web session
> > table.
> 
> You can tune thresholds and scale factors for that particular table
> using pg_autovacuum. If you lower them appropriately, the vacuum will be
> fired more often for that table - but don't lower them too much, just go
> step by step until you reach values that are fine for you.

That doesn't work well if autovac gets tied up vacuuming a very large
table. Granted, when that happens there are considerations about the
long-running vacuum transaction (prior to 8.2), but in many systems
you'll still get some use out of other vacuums.
-- 
Jim C. Nasby, Database Architect                   jim@nasby.net
512.569.9461 (cell)                         http://jim.nasby.net