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Re: CPU and RAM

From: "Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: CPU and RAM
Date: 2005-12-23 04:29:42
Message-ID: dofudn$1t0a$ (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
"Greg Stark" <gsstark(at)mit(dot)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.


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