Re: pg_plan_advice

On Thu, Mar 26, 2026 at 3:52 PM Lukas Fittl <lukas(at)fittl(dot)com> wrote:
> That said, reflecting on the change, I wonder if its odd that we're
> copying a string pointer instead of making an actual string copy. I
> think that's probably okay in practice?

Normally, all of planning happens in the same memory context. Under
GEQO, joins are planned in shorter-lived contexts that are reset, but
I don't think a new PlannerInfo can get created in one of those
short-lived contexts. At any rate, there's no point in having two
copies of the same string in the same memory context.

> I'm still 50/50 on the naming here, since we have the alternative sub
> plan that has an "alternative plan name" that's not that of the
> alternative itself, but rather the base plan that was utilized. But I
> see your concern regarding the naming being confusing in terms of what
> the "original" or "base" would actually refer to. I've also considered
> whether something like "alternative_plan_group" could make sense
> (since all alternative sub plans will have the same value), but maybe
> that conveys too much intent on what this is used for.

Let's go with this for now, and if a consensus emerges that I got it
wrong, we can always change it.

> That said, I think for now, to get the buildfarm happy again, v23/0001
> seems good.
>
> v23/0002 also looks good.

Thanks. Committed. Nothing has obviously broken so far, BUT even
machines like skink that were failing weren't failing on every run, so
it may be a while before we get a clear view of the situation --
unless of course this didn't fix it or even made things worse, in
which case we might find out a lot faster. Hopefully not, but then I
thought this was going to work the first time.

In the meanwhile, we should try to make a decision on what to do about
pg_collect_advice and pg_stash_advice.

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