Re: Gather Merge

On Tue, Mar 14, 2017 at 9:56 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> Cool, thanks for the review. I'm not quite confident that we've found
>> all of the bugs here yet, but I think we're moving in the right
>> direction.
>
> I guess the real question here is why isn't Gather Merge more like
> Append and MergeAppend? That is, why did you complicate matters
> by making it projection capable? That seems like a pretty random
> decision from here.

Well, then it would be inconsistent with plain old Gather. I thought
about going that route - ripping whatever projection logic Gather has
out and teaching the system that it's not projection-capable - but I
don't see what that buys us. It's pretty useful to be able to project
on top of Gather-type nodes, because they will often be at the top of
the plan, just before returning the results to the user.

--
Robert Haas
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