Re: Pushdown target list below gather node (WAS Re: WIP: Upper planner pathification)

On Thu, Mar 17, 2016 at 7:10 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> writes:
> > While reading above code changes, it looks like it is assuming that
subpath
> > and subplan will always be same (as it is verifying projection
capability
> > of subpath and attaching the tlist to subplan), but I think it is
possible
> > that subpath and subplan correspond to different nodes when gating
Result
> > node is added on to top of scan plan by create_scan_plan().
>
> A little more thought will show you that that's not actually relevant,
> because the tlist computation would have happened (or not) below the
> gating Result. If gating Results had an impact on
> apply_projection_to_path's decisions we'd have had to do something about
> that before this.
>

I understand that gating Results won't impact it, but it was just not
apparent from looking at the code I had referred. If you think it is quite
obvious thing, then we can leave the comment as it is.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com