Date: Tue, 10 Feb 2009 11:07:42 -0300
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Stefano Nichele <stefano.nichele@gmail.com>
Cc: pgsql-admin@postgresql.org
Subject: Re: strange autovacuum behaviour
Message-ID: <20090210140742.GG3708@alvh.no-ip.org>
References: <49906B4F.5040509@gmail.com>
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Stefano Nichele escribió:
> Hi All,
> I have a couple of questions about autovacuum/vacuum behavior.
>
> On my production system, I set autovacuum ON since it's pretty hard to
> me find a good timeframe for vacuum (the system is pretty busy over the day)
> Last week the system was really slow and running vacuum manually the
> performance was really improved.
> So now I would like to understand why autovacuum did not work as
> expected (at least for me). Any ideas ?

Maybe the autovacuum naptime was set too high.  Or perhaps the threshold
and scale settings were too high.  Maybe the vacuum_cost_delay for
autovacuum was too high.

> Why autovacuum (that was OFF) started ?  For preventing transaction ID
> wraparound ? Is it right that in such case all the tables are
> (auto)vacuumed ?

Not necessarily all tables; only those that require a vacuum to prevent
xid wraparound.  (It was all tables in 8.1, but this changed in 8.2).