Re: FOR UPDATE versus WITH --- change 8.4 too?

On Tuesday 27 October 2009 18:02:53 Robert Haas wrote:
> On Tue, Oct 27, 2009 at 10:50 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > In yesterday's discussions about FOR UPDATE there was some mention of
> > making it not propagate into WITH subqueries:
> > http://archives.postgresql.org/pgsql-hackers/2009-10/msg01540.php
> > That is, given
> > WITH w AS (SELECT * FROM foo) SELECT * FROM w, bar ... FOR UPDATE
> > should foo be locked FOR UPDATE or not? The current behavior is that
> > the code attempts to propagate FOR UPDATE into the WITH, and fails
> > (the parser rejects it in some cases, and the planner in others ---
> > AFAICT there is no case where it actually works). This is pretty
> > useless, and it's also at odds with the philosophy we adopted that WITH
> > queries execute independently of the primary query. So I think there
> > was consensus to change it to have FOR UPDATE ignore WITH references.
> >
> > What I'm wondering at the moment is if there's any objection to
> > back-patching the change into 8.4. Given the lack of any way to have a
> > working query depend on this behavior, it doesn't seem that there could
> > be a problem, but can anyone think of an objection I missed?
>
> If it doesn't have any effect anyway, what's the virtue of back-patching
> it?
>
> It seems like we might want to throw an error rather than silently
> ignoring it, but that obviously wouldn't be back-patchable.
Because it makes it impossible to use SELECT FOR UPDATE with a CTE atm? Which
very well can be considered a bug.

Andres