Re: pg_plan_advice

On Thu, Jan 8, 2026 at 2:14 PM Lukas Fittl <lukas@fittl.com> wrote:
> On Thu, Jan 8, 2026 at 10:22 AM Robert Haas <robertmhaas@gmail.com> wrote:
> > 0004: Comment update, bug fix to cost_index() per comment from Lukas.
>
> Thanks! I've tested this and this works as expected on current master
> with the updated pg_hint_plan code, and checking for tablesample in
> the code that sets the mask.

Nice!

> > How about checking rte->tablesample, as set_rel_pathlist does?
>
> Yeah, that works - its a bit inconvenient for two reasons, but I don't
> think that warrants a redesign:
>
> 1) get_relation_info_hook doesn't get a RangeTblEntry passed (like
> set_rel_pathlist_hook), but that's solvable by looking it up via
> simple_rte_array

That's a pretty normal thing to have to do in this kind of code, IMHO.

> 2) It requires maintaining a special case in the logic that says "make
> it parallel", vs the planner that is authoritative (i.e. if we add
> more special cases in the future, each extension will have to be
> updated to reflect that)

IMHO, this is a policy decision by the extension and so the logic
belongs in the extension. pg_plan_advice has no similar exception,
because it made a different policy decision.

Overall, I feel that your experiment here is a pretty compelling
argument for committing 0004 (the pgs_mask stuff). I'm not sure it's
quite time to do that yet, because maybe there are still some design
changes we want to consider for it, or maybe somebody else wants to
review first. But even if that patch did nothing other than get rid of
lots of complexity and copy-paste in pg_hint_plan, that would be
enough to justify this infrastructure. The fact that basically works
as intended for both pg_plan_advice and pg_hint_plan, despite them
having no common code, is a really good sign, IMHO.

--
Robert Haas
EDB: http://www.enterprisedb.com