Date: Fri, 26 Jul 2013 16:27:14 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: German Becker <german.becker@gmail.com>
Cc: "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
Subject: Re: Disk latency goes up during certaing pediods
Message-ID: <20130726202714.GK14652@eldon.alvh.no-ip.org>
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German Becker escribió:
> Hi list,
> 
> I am running Postgres 9.1 on Ubuntu 12.04. I have a dedicated disk for
> pg_xlog, using ext4 filesystem with journaling in writeback mode
> During high load times, the disk usage is arround 40%. The IO write time is
> constant at about 3ms. On certain occasions  roughly once in 15 days, the
> IO write time goes up to about 10ms. This makes the disk usage go up to
> almost 100%, probably saturation, and the INSERTS DELETES UPDATES run
> considerable slower than normal.This lasts for about 2 hours and then the
> latency goes back to 3ms and everything is normal again.
> Has anyone seen this behavior? What could be causing the increase in
> latency?

Can you correlate these episodes with autovacuum activity?  Or perhaps
backups are being taken (maybe a new base backup is taken every 15
days)?

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services


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