Re: Bug: Buffer cache is not scan resistant

From: Hannu Krosing <hannu(at)skype(dot)net>
To: Luke Lonergan <LLonergan(at)greenplum(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Grzegorz Jaskiewicz <gj(at)pointblue(dot)com(dot)pl>, PGSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Doug Rady <drady(at)greenplum(dot)com>, Sherry Moore <sherry(dot)moore(at)sun(dot)com>
Subject: Re: Bug: Buffer cache is not scan resistant
Date: 2007-03-05 09:10:24
Message-ID: 1173085824.3279.1.camel@localhost.localdomain
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Ühel kenal päeval, E, 2007-03-05 kell 03:51, kirjutas Luke Lonergan:
> Hi Tom,
>
> > Even granting that your conclusions are accurate, we are not
> > in the business of optimizing Postgres for a single CPU architecture.
>
> I think you're missing my/our point:
>
> The Postgres shared buffer cache algorithm appears to have a bug. When
> there is a sequential scan the blocks are filling the entire shared
> buffer cache. This should be "fixed".
>
> My proposal for a fix: ensure that when relations larger (much larger?)
> than buffer cache are scanned, they are mapped to a single page in the
> shared buffer cache.

How will this approach play together with synchronized scan patches ?

Or should synchronized scan rely on systems cache only ?

> - Luke
>
>
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