Re: pg_plan_advice

On Sat, Apr 4, 2026 at 5:34 AM Andrei Lepikhov <lepihov(at)gmail(dot)com> wrote:
> As you work on the code, please keep the pg_plan_advice issue [1] in
> mind. I came across it while designing the optimisation in [2]. Even if
> [2] is not added to the Postgres core, this still looks like a valid
> query plan and may be proposed by an extension. So, the hinting module
> should avoid conflicts with other extensions, just as pg_hint_plan does.
>
> [1] pg_plan_advice fails when NestLoop outer side is Sort over FunctionScan
> https://www.postgresql.org/message-id/78dd9572-7569-4025-984d-e07d7f381b6e@gmail.com
> [2] Try a presorted outer path when referenced by an ORDER BY prefix
> https://www.postgresql.org/message-id/19a9265c-c441-4a43-bc0d-dac533438da0%40gmail.com

I'll take a look at that issue when I have a free moment. We certainly
cannot promise in general that pg_plan_advice will be able to make
sense of plans that PostgreSQL's own planner does not produce; that
would require magical code. But there might be something that can be
done to ameliorate this particular instance.

By the way, I'm really glad you hit that error. That particular error
check is there precisely to find plans that pg_plan_advice isn't able
to understand, and it sounds like it is doing its job as intended.
Having problems isn't great, but knowing that you have problems is a
lot better than still having them but not knowing about it.

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