Re: Problem about postponing gathering partial paths for topmost scan/join rel

On Fri, Jul 15, 2022 at 5:00 PM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:

> On Fri, Jul 15, 2022 at 4:03 PM Richard Guo <guofenglinux(at)gmail(dot)com>
> wrote:
>
>> On Thu, Jul 14, 2022 at 10:02 PM Antonin Houska <ah(at)cybertec(dot)at> wrote:
>>
>>> I'd prefer a test that demonstrates that the Gather node at the top of
>>> the
>>> "subproblem plan" is useful purely from the *cost* perspective, rather
>>> than
>>> due to executor limitation.
>>
>>
>> This patch provides an additional path (Gather atop of subproblem) which
>> was not available before. But your concern makes sense that we need to
>> show this new path is valuable from competing on cost with other paths.
>>
>> How about we change to Nested Loop at the topmost? Something like:
>>
>
> Maybe a better example is that we use a small table 'c' to avoid the
> Gather node above scanning 'c', so that the path of parallel nestloop is
> possible to be generated.
>

Update the patch with the new test case.

Thanks
Richard