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Message-ID: <1360154987.89420.YahooMailNeo@web162901.mail.bf1.yahoo.com>
Date: Wed, 6 Feb 2013 04:49:47 -0800 (PST)
From: Kevin Grittner <kgrittn@ymail.com>
Reply-To: Kevin Grittner <kgrittn@ymail.com>
Subject: Re: postgresql.conf recommendations
To: "ac@hsk.hk" <ac@hsk.hk>, Josh Krupka <jkrupka@gmail.com>,
	Johnny Tan <johnnydtan@gmail.com>
Cc: Alex Kahn <alex@paperlesspost.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
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"ac@hsk.hk" <ac@hsk.hk> wrote:
> Johnny Tan <johnnydtan@gmail.com> wrote:

>>shared_buffers =3D 48GB# min 128kB

> From the postgresql.conf, I can see that the shared_buffers is
> set to 48GB which is not small,=A0 it would be possible that the
> large buffer cache could be "dirty", when a checkpoint starts, it
> would cause a checkpoint I/O spike.
>
>
> I would like to suggest you about using pgtune to get recommended
> conf for postgresql.

I have seen symptoms like those described which were the result of
too many dirty pages accumulating inside PostgreSQL shared_buffers.
It might be something else entirely in this case, but it would at
least be worth trying a reduced shared_buffers setting combined
with more aggressive bgwriter settings.=A0 I might try something like
the following changes, as an experiment:

shared_buffers =3D 8GB
bgwriter_lru_maxpages =3D 1000
bgwriter_lru_multiplier =3D 4

-Kevin


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