From: Tom Lane <tgl@sss.pgh.pa.us>
To: Merlin Moncure <mmoncure@gmail.com>
cc: Atri Sharma <atri.jiit@gmail.com>, Greg Stark <stark@mit.edu>,
	Ants Aasma <ants@cybertec.at>, Amit Kapila <amit.kapila@huawei.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Page replacement algorithm in buffer cache
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Comments: In-reply-to Merlin Moncure <mmoncure@gmail.com>
	message dated "Fri, 22 Mar 2013 14:05:56 -0500"
Date: Fri, 22 Mar 2013 15:52:05 -0400
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Merlin Moncure <mmoncure@gmail.com> writes:
> On Fri, Mar 22, 2013 at 1:13 PM, Atri Sharma <atri.jiit@gmail.com> wrote:
>> What is the general thinking? Is it time to start testing again and
>> thinking about improvements to the current algorithm?

> well, what problem are you trying to solve exactly?  the main problems
> I see today are not so much in terms of page replacement but spinlock
> and lwlock contention.

Even back when we last hacked on that algorithm, the concerns were not
so much about which pages it replaced as how much overhead and
contention was created by the management algorithm.  I haven't seen any
reason to think we have a problem with the quality of the replacement
choices.  The proposal to increase the initial usage count would
definitely lead to more overhead/contention, though, because it would
result in having to circle around all the buffers more times (on
average) to get a free buffer.

			regards, tom lane


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