| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>, Karim A Nassar <Karim(dot)Nassar(at)NAU(dot)EDU>, Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Delete query takes exorbitant amount of time |
| Date: | 2005-03-29 16:01:27 |
| Message-ID: | 1112112087.11750.984.camel@localhost.localdomain |
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| Lists: | pgsql-performance |
On Tue, 2005-03-29 at 10:31 -0500, Tom Lane wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)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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