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

On Thu, Mar 17, 2016 at 7:00 AM, Etsuro Fujita
<fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> BUT: we don't make any effort to ensure that local and remote values
> match, so system columns other than ctid and oid should not be retrieved
> from the remote server.

I agree.

> 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.

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