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From: cluster <skrald@amossen.dk>
To: pgsql-performance@postgresql.org
Subject: Re: Query only slow on first run
Date: Wed, 28 Nov 2007 21:16:08 +0100
Message-ID: <fikia6$26ql$1@news.hub.org> (raw)
In-Reply-To: <474CBF98.6070508@amossen.dk>
References: <fihgt1$1mmh$1@news.hub.org>
	<20071127165543.GY11978@crankycanuck.ca>
	<23999.1196184368@sss.pgh.pa.us>
	<fihn7h$2jrn$1@news.hub.org>
	<056501c83128$55d58a90$8e00a8c0@tridecap.com>
	<fii71p$oc1$1@news.hub.org>
	<20071127233833.GA24031@uio.no>
	<15029.1196209554@sss.pgh.pa.us>
	<474CBF98.6070508@amossen.dk>

>> I'm wondering why --- doesn't seem like it should take 6400msec to fetch
>> 646 rows, unless perhaps the data is just horribly misordered relative
>> to the index.   Which may in fact be the case ...

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

In general, I don't understand why the query is so I/O dependant as it 
apparently is.

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