From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Stephan Szabo <sszabo@megazone.bigpanda.com>
Cc: Karim A Nassar <Karim.Nassar@NAU.EDU>
Cc: Christopher Kings-Lynne <chriskl@familyhealth.com.au>
Cc: pgsql-performance@postgresql.org
Subject: Re: Delete query takes exorbitant amount of time
Date: Tue, 29 Mar 2005 17:01:27 +0100
Message-ID: <1112112087.11750.984.camel@localhost.localdomain> (raw)
In-Reply-To: <22527.1112110310@sss.pgh.pa.us>
References: <Pine.SOL.4.21.0503290120550.5642-100000@coruscant.cet.nau.edu>
<1112095776.11750.958.camel@localhost.localdomain>
<20050329054714.V50612@megazone.bigpanda.com>
<20050329061837.A51620@megazone.bigpanda.com>
<21616.1112108201@sss.pgh.pa.us>
<1112109880.11750.977.camel@localhost.localdomain>
<22527.1112110310@sss.pgh.pa.us>
On Tue, 2005-03-29 at 10:31 -0500, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > If action is NO ACTION or RESTRICT then
> > we need to SELECT at most 1 row that matches the criteria
> > which means we can use LIMIT 1
>
> > If action is CASCADE, SET NULL, SET DEFAULT then
> > we need to UPDATE or DELETE all rows that match the criteria
> > which means we musnt use LIMIT and need to use FOR UPDATE
>
> Huh? UPDATE/DELETE don't use FOR UPDATE. I think you have failed
> to break down the cases sufficiently. In particular it matters which
> side of the RI constraint you are working from ...
OK... too quick, sorry. I'll hand over to Stephan for a better and more
exhaustive explanation/analysis... but AFAICS we *can* always know the
correct formulation of the query prepare time, whether or not we do
currently.
Best Regards, Simon Riggs
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To: pgsql-performance@postgresql.org
Cc: simon@2ndquadrant.com, tgl@sss.pgh.pa.us, sszabo@megazone.bigpanda.com, Karim.Nassar@NAU.EDU, chriskl@familyhealth.com.au
Subject: Re: Delete query takes exorbitant amount of time
In-Reply-To: <1112112087.11750.984.camel@localhost.localdomain>
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