Re: "could not find pathkey item to sort" for TPC-DS queries 94-96

On 4/15/21 2:21 AM, Robert Haas wrote:
> On Wed, Apr 14, 2021 at 8:20 PM James Coleman <jtc331(at)gmail(dot)com> wrote:
>>> Hmm, could be. Although, the stack trace at issue doesn't seem to show
>>> a call to create_incrementalsort_plan().
>>
>> The changes to gather merge path generation made it possible to use
>> those paths in more cases for both incremental sort and regular sort,
>> so by "incremental sort" I read Tomas as saying "the patches that
>> brought in incremental sort" not specifically "incremental sort
>> itself".
>
> I agree. That's why I said "hmm, could be" even though the plan
> doesn't involve one.
>

Yeah, that's what I meant. The difference to pre-13 behavior is that we
now call generate_useful_gather_paths, which also considers adding extra
sort (unlike plain generate_gather_paths).

So now we can end up with "Gather Merge -> Sort" paths that would not be
considered before.

regards

--
Tomas Vondra
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