From: Andres Freund <andres@2ndquadrant.com>
Organization: 2ndquadrant.com
To: Jeff Janes <jeff.janes@gmail.com>
Subject: Re: Massive I/O spikes during checkpoint
Date: Tue, 10 Jul 2012 15:41:18 +0200
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Cc: pgsql-performance@postgresql.org, Maxim Boguk <maxim.boguk@gmail.com>,
	David Kerr <dmk@mr-paradox.net>
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	<201207101444.14887.andres@2ndquadrant.com>
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On Tuesday, July 10, 2012 03:36:35 PM Jeff Janes wrote:
> On Tue, Jul 10, 2012 at 5:44 AM, Andres Freund <andres@2ndquadrant.com> 
wrote:
> > On Tuesday, July 10, 2012 08:14:00 AM Maxim Boguk wrote:
> >> So kernel doesn't start write any pages out in background before it has
> >> at least 13Gb dirty pages in kernel memory.
> >> And at end of the checkpoint kernel trying flush all dirty pages to
> >> disk.
> > 
> > Thast not entirely true. The kernel will also writeout pages which
> > haven't been written to for dirty_expire_centisecs.
> 
> There seems to be many situations in which it totally fails to do that.
Totally as in diry pages sitting around without any io activity? Or just not 
agressive enough?

Currently its a bit hard to speculate about all without specifying the kernel 
because there have been massive rewrites of all that stuff in several kernels 
in the last two years...

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