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. ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
