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

On Fri, 8 Sept 2023 at 09:41, Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Tue, Sep 5, 2023 at 8:07 AM Richard Guo <guofenglinux@gmail.com> wrote:
> > Yeah, this seems an omission in commit 45be99f8.
>
> It's been a while, but I think I omitted this deliberately because I
> didn't really understand the value of it and wanted to keep the
> planning cost down.

I think the value is potentially not having to repeatedly execute some
expensive rescan to the nested loop join once for each outer-side
tuple.

The planning cost is something to consider for sure, but it seems
strange that we deemed it worthy to consider material paths for the
non-parallel input paths but draw the line for the parallel/partial
ones. It seems to me that the additional costs and the possible
benefits are the same for both.

David