Re: Worse perfomance on 8.2.0 than on 7.4.14

From: Rolf Østvik <rolfostvik(at)yahoo(dot)no>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Worse perfomance on 8.2.0 than on 7.4.14
Date: 2007-01-01 15:19:05
Message-ID: 20070101151905.55545.qmail@web26309.mail.ukl.yahoo.com
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--- Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> skrev:

> Rolf =?iso-8859-1?q?=D8stvik?= <rolfostvik(at)yahoo(dot)no>
> writes:
> > I have a simple query which uses 32ms on 7.4.14
> and 1015ms on 8.2.0.
>
> There's something awfully strange about that 8.2
> plan --- if it knew
> that it'd have to scan all of uut_result_subset
> (which it should have
> known, if the stats were up-to-date),

I can't really see the need for it to do an sequence
scan, but that is me not knowing how things work.

>why did it use
> an indexscan
> rather than a seqscan? Are you sure you haven't
> tweaked any parameters
> you didn't tell us about, such as setting
> enable_seqscan = off?

I haven't touched enable_seqscan.
It could be that i have forgotton to tell you about a
parameter i have tweaked, but i doubt it.

Best regards
Rolf Østvik

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