Re: Error-safe user functions

On Sat, Dec 10, 2022 at 9:20 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> > On 2022-Dec-09, Tom Lane wrote:
> >> ... So I think it might be
> >> okay to say "if you want soft error treatment for a domain,
> >> make sure its check constraints don't throw errors".
>
> > I think that's fine. If the user does, say "CHECK (value > 0)" and that
> > results in a soft error, that seems to me enough support for now. If
> > they want to do something more elaborate, they can write C functions.
> > Maybe eventually we'll want to offer some other mechanism that doesn't
> > require C, but let's figure out what the requirements are. I don't
> > think we know that, at this point.
>
> 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.
>
> regards, tom lane
>

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.