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Re: Seq scans status update

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Seq scans status update
Date: 2007-05-30 22:23:58
Message-ID: 1180563838.26915.192.camel@dogma.v10.wvs (view raw or flat)
Thread:
Lists: pgsql-patches
On Wed, 2007-05-30 at 17:45 -0400, Tom Lane wrote:
> According to Heikki's explanation here
> http://archives.postgresql.org/pgsql-patches/2007-05/msg00498.php
> each backend doing a heapscan would collect its own ring of buffers.
> You might have a few backends that are always followers, never leaders,
> and so never actually fetch any pages --- but for each backend that
> actually did any I/O there would be a separate ring.  In practice I'd
> expect the lead would "change hands" pretty often and so you'd see all
> the backends accumulating their own rings.
> 

Oh, I see what you mean. The rings will actually become sparsely
populated with many concurrent scans, and therefore, extend outside of
L2 cache.

Regards,
	Jeff Davis


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