From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
---|---|
To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
Cc: | Janning <ml(at)planwerk6(dot)de>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: checkpoint spikes |
Date: | 2010-06-11 19:48:54 |
Message-ID: | 20100611194854.GA23114@svana.org |
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Lists: | pgsql-general |
On Thu, Jun 10, 2010 at 04:00:54PM -0400, Greg Smith wrote:
>> 5. Does anybody know if I can set dirty_background_ratio to 0.5? As we
>> have 12 GB RAM and rather slow disks 0,5% would result in a maximum of
>> 61MB dirty pages.
>
> Nope. Linux has absolutely terrible controls for this critical
> performance parameter. The sort of multi-second spikes you're seeing
> are extremely common and very difficult to get rid of.
Another relevent parameter is /proc/sys/vm/dirty_writeback_centisecs.
By default linux only wakes up once every 5 seconds to check if there
is stuff to write out. I have found that reducing this tends to smooth
out bursty spikes. However, see:
http://www.westnet.com/~gsmith/content/linux-pdflush.htm
which indicates that kernel may try to defeat you here...
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Patriotism is when love of your own people comes first; nationalism,
> when hate for people other than your own comes first.
> - Charles de Gaulle
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