From: Qingqing Zhou <zhouqq@cs.toronto.edu>
To: pgsql-performance@postgresql.org
Subject: Re: CPU and RAM
Date: Thu, 22 Dec 2005 23:29:42 -0500
Message-ID: <dofudn$1t0a$1@news.hub.org> (raw)
References: <45b42ce40512211720t164ea389wa5bfd0cbae6c80e2@mail.gmail.com>
<878xuc8o6h.fsf@stark.xeocode.com>
"Greg Stark" <gsstark@mit.edu> wrote
>
> If the whole database is in RAM I wouldn't expect clustering to have any
> effect. Either you're doing a lot of merge joins or a few other cases
> where
> clustering might be helping you, or the cluster is helping you keep more
> of
> the database in ram avoiding the occasional disk i/o.
>
Hi Greg,
At first I think the same - notice that Tom has submitted a patch to scan a
whole page in one run, so if Harry tests against the cvs tip, he could see
the real benefits. For example, a index scan may touch 5000 tuples, which
involves 5000 pairs of lock/unlock buffer, no matter how the tuples are
distributed. After the patch, if the tuples belong to a few pages, then a
significant number of lock/unlock are avoided.
Regards,
Qingqing
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Subject: Re: CPU and RAM
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