From: Mark Lewis <mark.lewis@mir3.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Brian Choate <brianc@nimblefish.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Poor performance of delete by primary key
Date: Tue, 06 Sep 2005 10:04:38 -0700
Message-ID: <1126026278.3310.76.camel@archimedes> (raw)
In-Reply-To: <18162.1126020720@sss.pgh.pa.us>
References: <2F9239F5E316C54688FDA9814FF045D6EADACC@EXCHANGE.sf.nimblefish.com>
<18162.1126020720@sss.pgh.pa.us>
I had a similar problem, so I downloaded 8.1 from CVS, ran it on a
relatively gnarly dev workstation, imported a dump of my 8.0 database,
and ran my troublesome queries with the new EXPLAIN ANALYZE.
This process took about an hour and worked great, provided that you've
actually named your foreign key constraints. Otherwise, you'll find out
that there's a trigger for a constraint called $3 that's taking up all
of your time, but you won't know what table that constraint is on.
-- Mark
On Tue, 2005-09-06 at 11:32 -0400, Tom Lane wrote:
> "Brian Choate" <brianc@nimblefish.com> writes:
> > We are seeing a very strange behavior from postgres. For one of our very =
> > common tasks we have to delete records from a table of around 500,000 =
> > rows. The delete is by id which is the primary key. It seems to be =
> > consistently taking around 10 minutes to preform. This is totally out of =
> > line with the rest of the performance of the database.
>
> I'll bet this table has foreign-key references from elsewhere, and the
> referencing columns are either not indexed, or not of the same datatype
> as the master column.
>
> Unfortunately there's no very simple way to determine which FK is the
> problem. (In 8.1 it'll be possible to do that with EXPLAIN ANALYZE,
> but in existing releases EXPLAIN doesn't break out the time spent in
> each trigger ...) You have to just eyeball the schema :-(.
>
> regards, tom lane
>
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To: pgsql-performance@postgresql.org
Cc: mark.lewis@mir3.com, tgl@sss.pgh.pa.us, brianc@nimblefish.com
Subject: Re: Poor performance of delete by primary key
In-Reply-To: <1126026278.3310.76.camel@archimedes>
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