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Re: Query only slow on first run

From: "Steinar H(dot) Gunderson" <sgunderson(at)bigfoot(dot)com>
To: cluster <skrald(at)amossen(dot)dk>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Query only slow on first run
Date: 2007-11-28 20:34:42
Message-ID: 20071128203442.GB30600@uio.no (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, Nov 28, 2007 at 09:16:08PM +0100, cluster wrote:
> Hmm, actually I still don't understand why it takes 6400 ms to fetch the 
> rows. As far as I can see the index used is "covering" so that real row 
> lookups shouldn't be necessary.

The indexes don't contain visibility information, so Postgres has to look up
the row on disk to verify it isn't dead.

> Also, only the the random_numbers induces by questions with status = 1
> should be considered - and this part is a relatively small subset.

Again, you'll need to have a combined index if you want this to help you any.

/* Steinar */
-- 
Homepage: http://www.sesse.net/

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