Re: BUG #14505: explain verbose for postgresql_fdw

On Wed, Jan 18, 2017 at 5:27 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> jeff(dot)janes(at)gmail(dot)com writes:
> > The "Output:" line of explain verbose lists columns of foreign table that
> > are not actually output, or at least ought not be output.
>
> That's an optimization to avoid an unnecessary projection step. It has
> nothing to do with what's retrieved from the remote, and for that matter
> it's not specific to foreign tables.
>

Is all of that data actually being transferred from the foreign to the
local? If so, I don't think the optimization is a good choice in this
case. Do you know where can I find the relevant source code which decides
on this?

Cheers,

Jeff