Re: Odd system-column handling in postgres_fdw join pushdown patch

On 2016/03/19 4:51, Robert Haas wrote:
> On Thu, Mar 17, 2016 at 7:00 AM, Etsuro Fujita
> <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> So, I'd like to propose: (1) when tableoids are
>> requested from the remote server, postgres_fdw sets valid values for
>> them locally, instead (core should support that?)

> Sure.

>> and (2) when any of
>> xmins, xmaxs, cmins, and cmaxs are requested, postgres_fdw gives up
>> pushing down foreign joins. (We might be able to set appropriate values
>> for them locally the same way as for tableoids, but I'm not sure it's
>> worth complicating the code.) I think that would be probably OK,
>> because users wouldn't retrieve any such columns in practice.

> Now that seems like the wrong reaction. I mean, aren't these just
> going to be 0 or something? Refusing to push the join down seems
> strange.

OK, I'll modify the patch so that the join is pushed down even if any of
xmins, xmaxs, cmins, and cmaxs are requested. Do you think which one
should set values for these as well as tableoids, postgres_fdw or core?

Best regards,
Etsuro Fujita