Re: warn if GUC set to an invalid shared library

On Fri, Jul 22, 2022 at 03:26:47PM -0400, Tom Lane wrote:
> Justin Pryzby <pryzby(at)telsasoft(dot)com> writes:
> > On Fri, Jul 22, 2022 at 03:00:23PM -0400, Tom Lane wrote:
> >> Shouldn't you be doing this when the source is PGC_S_TEST, instead?
>
> > That makes sense, but it doesn't work for ALTER SYSTEM, which uses PGC_S_FILE.
>
> Hmph. I wonder if we shouldn't change that, because it's a lie.

I think so, and I was going to raise this question some months ago when
I first picked up the patch.

The question is, which behavior do we want ?

postgres=# ALTER SYSTEM SET default_table_access_method=abc;
2022-07-22 15:24:55.445 CDT client backend[27938] psql ERROR: invalid value for parameter "default_table_access_method": "abc"
2022-07-22 15:24:55.445 CDT client backend[27938] psql DETAIL: Table access method "abc" does not exist.
2022-07-22 15:24:55.445 CDT client backend[27938] psql STATEMENT: ALTER SYSTEM SET default_table_access_method=abc;

That behavior differs from ALTER SYSTEM SET shared_preload_libraries,
which supports first seting the GUC and then installing the library. If
that wasn't supported, I think we'd just throw an error and avoid the
possibility that the server can't start.

It caused no issue when I changed:

/* Check that it's acceptable for the indicated parameter */
if (!parse_and_validate_value(record, name, value,
- PGC_S_FILE, ERROR,
+ PGC_S_TEST, ERROR,
&newval, &newextra))

I'm not sure where to go from here.

--
Justin