Hi, On 2021-09-15 16:51:37 -0400, Tom Lane wrote: > The other problem here is that a simple call-this-instead-of-that > top-level hook doesn't seem all that useful anyway, because it leaves > you with the task of duplicating a huge amount of functionality that > you're then going to make some tweaks within. That's already an issue > when you're just thinking about the grammar, and if you have to buy > into it for parse analysis too, I doubt that it's going to be very > practical. If, say, you'd like to support some weird function that > requires special parsing and analysis rules, I don't see how you get > that out of this without first duplicating a very large fraction of > src/backend/parser/.
We do have a small amount of infrastructure around this - the hackery that plpgsql uses. That's not going to help you with everything, but I think it should be be enough to recognize e.g. additional top-level statements. Obviously not enough to intercept parsing deeper into a statement, but at least something. And parse-analysis for some types of things will be doable with the current infrastructure, by e.g. handling the new top-level statement in the hook, and then passing the buck to the normal parse analysis for e.g. expressions in that. Obviously not going to get you that far... > (As a comparison point, we do have a top-level hook for replacing > the planner; but I have never heard of anyone actually doing so. > There are people using that hook to *wrap* the planner with some > before-and-after processing, which is quite a different thing.) Citus IIRC has some paths that do not end up calling into the standard planner, but only for a few simplistic cases. > I don't have any better ideas to offer :-( ... but I very much fear > that the approach proposed here is a dead end. I unfortunately don't see a good way forward without changing the way we do parsing on a more fundamental level :(. Greetings, Andres Freund