From: Janning Vygen <vygen@gmx.de>
To: Marc G. Fournier <scrappy@postgresql.org>
Cc: pgsql-sql@postgresql.org
Subject: Re: How do FKs work?
Date: Sun, 10 Oct 2004 14:24:32 +0200
Message-ID: <200410101424.32846.vygen@gmx.de> (raw)
In-Reply-To: <20041009214318.V54093@ganymede.hub.org>
References: <20041009145332.D54093@ganymede.hub.org>
<6093.1097367833@sss.pgh.pa.us>
<20041009214318.V54093@ganymede.hub.org>
Am Sonntag, 10. Oktober 2004 02:43 schrieb Marc G. Fournier:
> On Sat, 9 Oct 2004, Tom Lane wrote:
> > "Marc G. Fournier" <scrappy@hub.org> writes:
> >> Have a table with two FKs on it ... 2 different fields in the table
> >> point to the same field in another table ...
> >>
> >> When I do an 'EXPLAIN ANALYZE DELETE FROM table WHERE field = #;', it
> >> never comes back ... or, at lesat, takes a *very* long time ...
> >
> > Do you have indexes on the referencing columns? Are they exactly the
> > same datatype as the referenced column? You can get really awful plans
> > for the FK-checking queries if not.
>
> Yup, that was my first thought ... running SELECT's joining the two tables
> on the FK fields shows indices being used, and fast times ...
Why dont you try EXPLAIN DELETE ... (without ANALYZE). it shows you the plan
without executing it and shows you which index is missing.
janning
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-sql@postgresql.org
Cc: vygen@gmx.de, scrappy@postgresql.org
Subject: Re: How do FKs work?
In-Reply-To: <200410101424.32846.vygen@gmx.de>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox