Re: Disk latency goes up during certaing pediods

"...like if the disk/filesystem gets slower during one hour or so"

What about a different scheduled task on the system, not necessarily
Postgres related?

On Mon, Jul 29, 2013 at 9:17 AM, German Becker <german(dot)becker(at)gmail(dot)com>wrote:

> 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
>>
>
>