Re: why not parallel seq scan for slow functions

On Wed, Aug 16, 2017 at 7:23 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Tue, Aug 15, 2017 at 7:15 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Sat, Aug 12, 2017 at 9:18 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>> I think skipping a generation of gather paths for scan node or top
>>> level join node generated via standard_join_search seems straight
>>> forward, but skipping for paths generated via geqo seems to be tricky
>>> (See use of generate_gather_paths in merge_clump). Assuming, we find
>>> some way to skip it for top level scan/join node, I don't think that
>>> will be sufficient, we have some special way to push target list below
>>> Gather node in apply_projection_to_path, we need to move that part as
>>> well in generate_gather_paths.
>>
>> I don't think that can work, because at that point we don't know what
>> target list the upper node wants to impose.
>>
>
> I am suggesting to call generate_gather_paths just before we try to
> apply projection on paths in grouping_planner (file:planner.c;
> line:1787; commit:004a9702). Won't the target list for upper nodes be
> available at that point?

Oh, yes. Apparently I misunderstood your proposal.

--
Robert Haas
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