Re: Disk latency goes up during certaing pediods

Alvaro,

Thanks for your reply. I believe that the only possibility is autovacum
activity I will check that. Anyway what puzzles me is that
the throughput does not increase like i might expect if there where high
VACUUM activity, only the WAIT TIME and thus the UTILIZATION. Is like if
the disk/filesystem gets slower during one hour or so...

On Fri, Jul 26, 2013 at 5:27 PM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>wrote:

> 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
>