Re: search_plan_tree(): handling of non-leaf CustomScanState nodes causes segfault

David Geier <david(at)swarm64(dot)com> writes:
> On 18.01.21 19:46, Tom Lane wrote:
>> Hm. I agree that we shouldn't simply assume that ss_currentRelation
>> isn't null. However, we cannot make search_plan_tree() descend
>> through non-leaf CustomScan nodes, because we don't know what processing
>> is involved there. We need to find a scan that is guaranteed to return
>> rows that are one-to-one with the cursor output. This is why the function
>> doesn't descend through join or aggregation nodes, and I see no argument
>> by which we should assume we know more about what a customscan node will
>> do than we know about those.

> That makes sense. Thanks for the explanation.

OK, cool. I was afraid you'd argue that you really needed your CustomScan
node to be transparent in such cases. We could imagine inventing an
additional custom-scan-provider callback to embed the necessary knowledge,
but I'd rather not add the complexity until someone has a use-case.

> I updated the patch to match your proposal.

WFM, will push in a bit.

regards, tom lane