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Re: postgresql meltdown on

From: Manfred Koizar <mkoi-pg(at)aon(dot)at>
To: "Kendrick C(dot) Wilson" <kendrick_wilson(at)hotmail(dot)com>
Cc: chriskl(at)familyhealth(dot)com(dot)au, pgsql-performance(at)postgresql(dot)org
Subject: Re: postgresql meltdown on
Date: 2003-03-19 19:52:21
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Tue, 18 Mar 2003 09:19:44 -0600, "Kendrick C. Wilson"
<kendrick_wilson(at)hotmail(dot)com> wrote:
>If there are multiple values, the location of the first record is found in 
>the indexFile.
>Then dataFile is scanned until this != 'whatever';

Nice, but unfortunately not true for Postgres.  When you do the first
UPDATE after CLUSTER the new version of the changed row(s) are written
to the end of the dataFile (heap relation in Postgres speech).  So the
*index* has to be scanned until this != 'whatever'.

>Clustering is good for queries that return multiple [rows with the same search] values.

Yes.  With clustering you can expect that most of the tuples you want
are near to each other and you find several of them in the same page.


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