Re: query taking much longer since Postgres 8.4 upgrade

From: "Davenport, Julie" <JDavenport(at)ctcd(dot)edu>
To: "tv(at)fuzzy(dot)cz" <tv(at)fuzzy(dot)cz>
Cc: Merlin Moncure <mmoncure(at)gmail(dot)com>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: query taking much longer since Postgres 8.4 upgrade
Date: 2011-03-23 14:44:31
Message-ID: FC3C063A33946548BBC77657D3A2AF750F135E00@ctc385b.campus.ctcd.org
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Here is the explain plan of the new query (same as original but with changes to the Date subquery to use ::date instead of to_char to truncate the time portion), when it is run after doing these 2 sets first:

set work_mem='8MB';

set enable_nestloop = false;

explain plan (8.4): http://explain.depesz.com/s/tw8

thanks again for the help.
Julie

-----Original Message-----
From: tv(at)fuzzy(dot)cz [mailto:tv(at)fuzzy(dot)cz]
Sent: Monday, March 21, 2011 11:33 AM
To: Davenport, Julie
Cc: Merlin Moncure; Tomas Vondra; pgsql-general(at)postgresql(dot)org
Subject: RE: [GENERAL] query taking much longer since Postgres 8.4 upgrade

> Incredible! Setting enable_nestloop off temporarily for the run of this
> script made it run in less than a minute (had been running in 10 or 11
> minutes). I think you have found a solution for many of my slow running
> scripts that use these same type of joins. Thanks again.
> Julie

Nice. Can you post EXPLAIN ANALYZE again, so that we can see why this plan
was evaluated as as more expensive before disabling nested loops?

regards
Tomas

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