To: Chris <lists@deksai.com>
cc: pgsql-performance@postgresql.org
Subject: Re: stats collector suddenly causing lots of IO 
In-reply-to: <20100413170105.GA29571@chris-laptop.a2hosting.com> 
References: <20100413170105.GA29571@chris-laptop.a2hosting.com>
Comments: In-reply-to Chris <lists@deksai.com>
	message dated "Tue, 13 Apr 2010 13:01:06 -0400"
Date: Thu, 15 Apr 2010 18:21:10 -0400
Message-ID: <25790.1271370070@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Chris <lists@deksai.com> writes:
> I have a lot of centos servers which are running postgres.  Postgres isn't used
> that heavily on any of them, but lately, the stats collector process keeps
> causing tons of IO load.  It seems to happen only on servers with centos 5.
> The versions of postgres that are running are:

> 8.1.18
> 8.2.6
> 8.3.1
> 8.3.5
> 8.3.6
> 8.3.7
> 8.3.8
> 8.3.9
> 8.4.2
> 8.4.3

Do these different server versions really all show the problem to the
same extent?  I'd expect 8.4.x in particular to be cheaper than the
older branches.  Are their pgstat.stat files all of similar sizes?
(Note that 8.4.x keeps pgstat.stat under $PGDATA/pg_stat_tmp/ whereas
in earlier versions it was under $PGDATA/global/.)

If your applications create/use/drop a lot of tables (perhaps temp
tables) then bloat of the pgstat.stat file is to be expected, but
it should get cleaned up by vacuum (including autovacuum).  What is
your vacuuming policy on these servers ... do you use autovacuum?

			regards, tom lane