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Re: PG 8.3 and large shared buffer settings

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: Greg Smith <gsmith(at)gregsmith(dot)com>
Cc: Dan Sugalski <dan(at)sidhe(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: PG 8.3 and large shared buffer settings
Date: 2009-09-26 19:16:52
Message-ID: f67928030909261216r4e3a1ad7r5821f02f583c3206@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Sat, Sep 26, 2009 at 8:19 AM, Greg Smith <gsmith(at)gregsmith(dot)com> wrote:
>
> Another problem spot are checkpoints.  If you dirty a very large buffer
> cache, that whole thing will have to get dumped to disk eventually, and on
> some workloads people have found they have to reduce shared_buffers
> specifically to keep this from being too painful.

Hi Greg,

Is this the case even if checkpoint_completion_target is set close to 1.0?

If you dirty buffers fast enough to dirty most of a huge
shared_buffers area between checkpoints, then it seems like lowering
the shared_buffers wouldn't reduce the amount of I/O needed, it would
just shift the I/O from checkpoints to the backends themselves.

It looks like checkpoint_completion_target was introduced in 8.3.0

Cheers,

Jeff

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Subject: Re: PG 8.3 and large shared buffer settings
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