Date: Sat, 29 Oct 2005 09:49:47 -0500
From: Bruno Wolff III <bruno@wolff.to>
To: Michael Fuhr <mike@fuhr.org>
Cc: Martin Lesser <ml-pgsql@bettercom.de>,
	pgsql-performance@postgresql.org
Subject: Re: Effects of cascading references in foreign keys
Message-ID: <20051029144947.GB21068@wolff.to>
Mail-Followup-To: Bruno Wolff III <bruno@wolff.to>,
	Michael Fuhr <mike@fuhr.org>, Martin Lesser <ml-pgsql@bettercom.de>,
	pgsql-performance@postgresql.org
References: <87acgszihk.fsf@nb-aspire.bettercom.de>
	<20051029142432.GA79557@winnie.fuhr.org>
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On Sat, Oct 29, 2005 at 08:24:32 -0600,
  Michael Fuhr <mike@fuhr.org> wrote:
> > Does an UPDATE of e.g. m_fld1 in t_master cause a 'lookup' in all tables
> > which have a cascading update-rule or is this 'lookup' only triggered if
> > the referenced column in t_master is explicitly updated?
> 
> My tests suggest that a lookup on the referring key is done only
> if the referenced key is changed.  Here's an example from 8.1beta4;
> I used this version because EXPLAIN ANALYZE shows triggers and the
> time spent in them, but I see similar performance characteristics
> in earlier versions.  I've intentionally not put an index on the
> referring column to make lookups on it slow.

It looks like this feature was added last May, so I think it only applies
to 8.1.