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

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.

...Robert