Re: Considering fractional paths in Append node

Hi, Andrei!

On Fri, Dec 6, 2024 at 10:13 AM Andrei Lepikhov <lepihov(at)gmail(dot)com> wrote:
>
> On 12/6/24 13:48, Andrei Lepikhov wrote:
> > On 11/2/24 01:18, Nikita Malakhov wrote:
> >> I've corrected failing test and created a patch at Commitfest:
> >> https://commitfest.postgresql.org/51/5361/ <https://
> >> commitfest.postgresql.org/51/5361/>
> > I have played around with this feature, which looks promising for such a
> > tiny change. It provides a 'bottom boundary' recommendation for
> > appending subpaths, participating in the 'fractional branch' of paths.
> > As I see it works consistently with the plans, created for plain tables
> > filled with similar data.
> > According to the proposal to change SeqScan logic, IMO, Andy is right.
> > But it is a separate improvement because it wouldn't work in the case of
> > LIMIT 10 or 100, as the newly added regression tests demonstrate.
> > I think this feature gives sensible profit for partitionwise paths.
> > Pushing this knowledge into subpaths could help postgres_fdw to reduce
> > network traffic.
> >
> See the attached patch: regression tests added; *_ext function removed -
> I think we wouldn't back-patch it into minor releases.

Thank you for revising this patch. I've a couple of questions for you.
1. You revise get_cheapest_fractional_path() to reject parametrized
paths in all the cases. Are you sure this wouldn't affect other
callers of this function?
2. As usage of root->tuple_fraction RelOptInfo it has been criticized,
do you think we could limit this to some simple cases? For instance,
check that RelOptInfo is the final result relation for given root.

Links.
https://www.postgresql.org/message-id/871q0fvbje.fsf%40163.com

------
Regards,
Alexander Korotkov
Supabase