Re: Foreign join pushdown vs EvalPlanQual

On Wed, Dec 9, 2015 at 3:22 AM, Etsuro Fujita
<fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> Sorry, my explanation might be not enough, but I'm not saying to hide the
> subplan. I think it would be better to show the subplan somewhere in the
> EXPLAIN outout, but I'm not sure that it's a good idea to show that in the
> current form. We have two plan trees; one for normal query execution and
> another for EvalPlanQual testing. I think it'd be better to show the
> EXPLAIN output the way that allows users to easily identify each of the plan
> trees.

It's hard to do that because we don't identify that internally
anywhere. Like I said before, the possibility of a ForeignScan having
an outer subplan is formally independent of the new EPQ stuff, and I'd
prefer to maintain that separation and just address this with
documentation.

Getting this bug fixed has been one of the more exhausting experiences
of my involvement with PostgreSQL, and to be honest, I think I'd like
to stop spending too much time on this now and work on getting the
feature that this is intended to support working. Right now, the only
people who can have an opinion on this topic are those who are
following this thread in detail, and there really aren't that many of
those. If we get the feature - join pushdown for postgres_fdw -
working, then we might get some feedback from users about what they
like about it or don't, and certainly if this is a frequent complaint
then that bolsters the case for doing something about it, and possibly
also helps us figure out what that thing should be. On the other
hand, if we don't get the feature because we're busy debating
interface details related to this patch, then none of these details
matter anyway because nobody except developer is actually running the
code in question.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company