Re: Fix BUG #17335: Duplicate result rows in Gather node

Thanks for having a look at this.

On Fri, 4 Feb 2022 at 13:48, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> I think the actual rule is: every path under a Gather or GatherMerge
> must be parallel-safe.

I've adjusted the patch so that it counts parallel_aware and
parallel_safe Paths independently and verifies everything below a
Gather[Merge] is parallel_safe.

The diff stat currently looks like:

src/backend/optimizer/plan/createplan.c | 230
1 file changed, 230 insertions(+)

I still feel this is quite a bit of code for what we're getting here.
I'd be more for it if the path traversal function existed for some
other reason and I was just adding the callback functions and Asserts.

I'm keen to hear what others think about that.

David