On 30/8/2025 23:51, Tom Lane wrote:
> PG Bug reporting form <noreply@postgresql.org> writes:
>> The following script:
> In some sense the "right" fix would be to do SubPlan generation
> later, when we have statistics available for the Vars of the
> parent query. But that seems like a rather large task, and
> we'd surely not wish to back-patch the results.
I'd vote to go this direction in the next version.
Implementing memoisation of subplans to reduce the number of subplan
evaluations, I encountered the same problem: the number of groups in the
parameter set can't be estimated during subplan planning.
I resolved this issue by employing upper_paths_hook to decide the
addition of Memoise nodes into subplans at the end of upper query planning.
But it is not an in-core solution and has a flaw with multi-level
references.
So, it would be better to prepare as much PlannerInfo's info, as
possible (base rels, maybe query tree?) before filling RelOptInfos with
potential paths.
--
regards, Andrei Lepikhov
