Funnily enough, you could replace "LLM query planner" with just "query planner" and this comment would still hold true
I've literally been saying "I can't believe the date is X and we still have to put up with this" for around 25 years now.
By people with a specific skill set. LLMs generation can also be fixed and verified by people with a certain skill set, and non-deterministic computing doesn't automatically mean unpredictable. When people say that the LLMs are a black box, it means unpredictability in unknown situations.
You do structured output, input validation, output validation, lower temperature, limit decisions, RL, etc. to increase predictability to near certainty. It's just statistics after all. Or you can as well generate the code to do the job.
It's just that the required skill set is a different one to do those things, and unusual in the context of DB administration.
I just find the "all llms are non dererministic and therefore unreliable" narrative a bit backwards. All software that has more than 0 users needs to deal with non-determinism anyway :)
From a completely technical perspective, we have a rough idea how the LLMs work, and improving a system requires measuring outcomes and you don't necessarily need to understand the mechanism.
EXPLAIN ANALYZE against data that's similar in size to prod checks a query written by an LLM as good as anything we can write... but, yes, you're right, we still didn't solve the halting problem - neither the LLMs.
Query planner feels pretty LLM-esque already
A bad query plan is not your typical kind of bug. I would definitely not call it fixable. Query planners are inherently dealing with estimations and approximations. If the query planners estimation is off, you're screwed.
Unless you come up with a way to cheaply determine exactly how many rows a query will return, bad query plans will still exist.