Re: BUG #17376: Adding unique column with a function() default results in "could not read block 0 in file" error

Japin Li <japinli(at)hotmail(dot)com> writes:
> On Fri, 21 Jan 2022 at 17:22, PG Bug reporting form <noreply(at)postgresql(dot)org> wrote:
>> The error message content returned is what I suspect of being a bug, not so
>> much that this SQL didn't work.

> +1. The error message makes user confused IMO, maybe we can fix it, but I have
> no idea for this. Any suggestion is welcomed.

Yeah. Ideally we'd throw an error along the lines of "can't access a
table that's in process of being altered". The SELECT inside the function
is not part of the ALTER TABLE machinery and ought to be locked out.
However, I fear we don't have adequate infrastructure to tell which
table accesses *are* part of the ALTER TABLE machinery and which aren't.
Maybe it'd be sufficient to check for an active ALTER TABLE in the
parser, but I'm not sure.

regards, tom lane