Re: Error-safe user functions

Corey Huinker <corey(dot)huinker(at)gmail(dot)com> writes:
> On Sat, Dec 10, 2022 at 9:20 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> A fallback we can offer to anyone with such a problem is "write a
>> plpgsql function and wrap the potentially-failing bit in an exception
>> block". Then they get to pay the cost of the subtransaction, while
>> we're not imposing one on everybody else.

> That exception block will prevent parallel plans. I'm not saying it isn't
> the best way forward for us, but wanted to make that side effect clear.

Hmm. Apropos of that, I notice that domain_in is marked PARALLEL SAFE,
which seems like a bad idea if it could invoke not-so-parallel-safe
expressions. Do we need to mark it less safe, and if so how much less?

Anyway, assuming that people are okay with the Not Our Problem approach,
the patch is pretty trivial, as attached. I started to write an addition
to the CREATE DOMAIN man page recommending that domain CHECK constraints
not throw errors, but couldn't get past the bare recommendation. Normally
I'd want to explain such a thing along the lines of "For example, X won't
work" ... but we don't yet have any committed features that depend on
this. I'm inclined to leave it like that for now. If we don't remember
to fix it once we do have some features, I'm sure somebody will ask a
question about it eventually.

regards, tom lane