Re: Patch to support SEMI and ANTI join removal

David Rowley <dgrowleyml@gmail.com> writes:
> On Fri, Sep 12, 2014 at 3:35 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>> I haven't read the patch, but I think the question is why this needs
>> to be different than what we do for left join removal.

> I discovered over here ->
> http://www.postgresql.org/message-id/CAApHDvo5wCRk7uHBuMHJaDpbW-b_oGKQOuisCZzHC25=H3__fA@mail.gmail.com
> during the early days of the semi and anti join removal code that the
> planner was trying to generate paths to the dead rel. I managed to track
> the problem down to eclass members still existing for the dead rel. I guess
> we must not have eclass members for outer rels? or we'd likely have seen
> some troubles with left join removals already.

Mere existence of an eclass entry ought not cause paths to get built.
It'd be worth looking a bit harder into what's happening there.
        regards, tom lane