Re: Queries taking ages in PG 8.1, have been much faster in PG<=8.0

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Markus Wollny" <Markus(dot)Wollny(at)computec(dot)de>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Queries taking ages in PG 8.1, have been much faster in PG<=8.0
Date: 2005-12-01 16:26:04
Message-ID: 11568.1133454364@sss.pgh.pa.us
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"Markus Wollny" <Markus(dot)Wollny(at)computec(dot)de> writes:
> My current problem is that rewriting hundreds of queries, some of them
> quite a bit more complex than this one, but all of them using the same
> general scheme, would take quite a lot of time - and I'm expected to
> hand over the survey results ASAP. So I will obviously have to do a
> rewrite if there's just no other way, but I wondered if there might be
> some other option that would allow me to point the planner in the right
> direction so it would behave the same as in the previous versions,
> namely 8.0?

It looks like "set enable_nestloop = 0" might be a workable hack for
the immediate need. Once you're not under deadline, I'd like to
investigate more closely to find out why 8.1 does worse than 8.0 here.

regards, tom lane

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