Re: our buffer replacement strategy is kind of lame

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: our buffer replacement strategy is kind of lame
Date: 2011-08-14 17:11:01
Message-ID: 28052.1313341861@sss.pgh.pa.us
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Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Sat, Aug 13, 2011 at 11:14 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I agree that something's missing.

> I'm quoting you completely out of context here, but yes, something is missing.

> We can't credibly do one test on usage count in shared buffers and
> then start talking about how buffer management is all wrong.

More generally: the originally presented facts suggest that there might
be value in improving the "buffer access strategy" code that keeps
particular operations from using all of shared_buffers. It seems to me
to be a giant and unsubstantiated leap from that to the conclusion that
there's anything wrong with the clock sweep algorithm. Moreover,
several of the proposed "fixes" amount to reversion to methods that
we already know are less good than the clock sweep, because we already
tried them years ago. So I've been quite unimpressed with the quality
of discussion in this thread.

regards, tom lane

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