Re: pg_plan_advice

On Thu, Mar 26, 2026 at 9:55 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> Whoops. Obviously got the wrong thing stuck in my cut and paste buffer
> when I was writing that. Thanks for checking it. I'm going to go ahead
> and commit this, because I'm pretty confident that it's correct, and
> the rest of these patches are not going to fix the buildfarm
> instability without it, and I'm pretty sure multiple committers are
> pretty tired of seeing these test_plan_advice failures already.

Done.

> Right, the comment isn't quite correct. I don't think your rewording
> is quite right either, though, because there's really no reason to
> mention plan_name here at all. I'll adjust it.

Done and committed, after also adjusting the memory context handling
to avoid re-breaking GEQO.

> The dangling pointers are a good point; I agree that's bad. However,
> I'd be more inclined to fix it by nulling out the alternative_root
> pointers at the end of set_plan_references. I think that would just be
> the case where root->isAltSubplan[ndx] && root->isUsedSubplan[ndx].
> The reason I'm reluctant to just store the name is that there's not an
> easy way to find a PlannerInfo by name. I originally proposed an
> "allroots" list in PlannerGlobal, but we went with subplanNames on
> Tom's suggestion. I subsequently realized that this kind of stinks for
> code that is trying to use this infrastructure for anything, for
> exactly this reason, but Tom never responded and I never pressed the
> issue. But I think we're boxing ourselves into a corner if we just
> keep storing names that can't be looked up everywhere. It doesn't
> matter for the issue before us, so maybe doing as you say here is the
> right idea just so we can move forward, but I think we're probably
> kidding ourselves a little bit.

Here's a new version, where I've replaced alternative_root by
alternative_plan_name, serving the same function.

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