Message-ID: <4D4C4E15.20401@agliodbs.com>
Date: Fri, 04 Feb 2011 11:05:57 -0800
From: Josh Berkus <josh@agliodbs.com>
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To: pgsql-performance@postgresql.org
Subject: Write-heavy pg_stats_collector on mostly idle server
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All,

Seeing an issue which is new on me.  On a mostly idle PostgreSQL server,
the stats collector is rewriting the entire stats file twice per second.

Version: 8.4.4
Server: Ubuntu, kernel 2.6.32
Server set up: ApacheMQ server.  25 databases, each of which hold 2-3
tables.
Filesystem: Ext4, defaults
Active connections: around 15
Autovacuum settings: defaults

Symptoms: on a server which gets around 20 reads and 15 writes per
minute, we are seeing average 500K/second writes by the stats collector
to pg_stat.tmp.  pg_stat.tmp is around 270K.

An strace of the stats collector process shows that the stats collector
is, in fact, rewriting the entire stats file twice per second.

Anyone seen anything like this before?

-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com