Re: Should consider materializing the cheapest inner path in consider_parallel_nestloop()

On Thu, Jul 18, 2024 at 4:00 PM Alexander Lakhin <exclusion(at)gmail(dot)com> wrote:
> Please look at a recent buildfarm failure [1], which shows some
> instability of that test addition:
> -- the joinrel is not parallel-safe due to the OFFSET clause in the subquery
> explain (costs off)
> select * from tenk1 t1, (select * from tenk2 t2 offset 0) t2 where t1.two > t2.two;
> - QUERY PLAN
> --------------------------------------------
> + QUERY PLAN
> +-------------------------------------------------
> Nested Loop
> Join Filter: (t1.two > t2.two)
> - -> Gather
> - Workers Planned: 4
> - -> Parallel Seq Scan on tenk1 t1
> + -> Seq Scan on tenk2 t2
> -> Materialize
> - -> Seq Scan on tenk2 t2
> + -> Gather
> + Workers Planned: 4
> + -> Parallel Seq Scan on tenk1 t1
> (7 rows)

Thank you for the report and investigation. Will have a look.

Thanks
Richard