On Tue, 29 Mar 2005, Simon Riggs wrote:

> On Tue, 2005-03-29 at 10:31 -0500, Tom Lane wrote:
> > Simon Riggs <[EMAIL PROTECTED]> 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.

We currently use FOR UPDATE on the NO ACTION check, because otherwise we
might get back a row that's already marked for deletion by a concurrent
transaction.  I think that's intended to wait and succeed, not fail.

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