To: Uwe Bartels <uwe.bartels@gmail.com>
cc: pgsql-admin@postgresql.org
Subject: Re: blocking automatic vacuum 
In-reply-to: <AANLkTikICmG_zdZRULEsoBSvxzRuPxwPgomRUsAVWgWl@mail.gmail.com> 
References: <AANLkTikICmG_zdZRULEsoBSvxzRuPxwPgomRUsAVWgWl@mail.gmail.com>
Comments: In-reply-to Uwe Bartels <uwe.bartels@gmail.com>
	message dated "Tue, 22 Jun 2010 15:36:44 +0200"
Date: Tue, 22 Jun 2010 10:48:03 -0400
Message-ID: <1494.1277218083@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Uwe Bartels <uwe.bartels@gmail.com> writes:
> last ween i've seen a blocking "automatic vacuum".
> as i understood, this is not supposed to happen. in the past i saw vacuum
> processes disappear, in case of the need of a lock.

What that sounds like is it was an anti-wraparound vacuum.  Autovacuum
won't cancel those to avoid delaying other processes.

Now, RowExclusiveLock doesn't conflict with an autovacuum, so there is
more going on here than you've showed us.  The other obvious question is
how did you get to the point where an anti-wraparound vacuum became
necessary.

I speculate that you are doing something that does conflict with vacuum
(ie, SHARE UPDATE EXCLUSIVE lock or higher), and are doing it so often
that regular autovacuum runs on the table never manage to complete.
This is very bad, because you're going to have a serious bloat problem
if autovac keeps getting canceled.  You need to look at what sort of DDL
you are repetitively executing on that table, and find a way to do it a
lot less often.

			regards, tom lane