Re: warn if GUC set to an invalid shared library

On Tue, Feb 1, 2022 at 11:06 PM Maciek Sakrejda <m.sakrejda@gmail.com>
wrote:

> I tried running ALTER SYSTEM and got the warnings as expected:
>
> postgres=# alter system set shared_preload_libraries =
> no_such_library,not_this_one_either;
> WARNING:  could not access file "$libdir/plugins/no_such_library"
> WARNING:  could not access file "$libdir/plugins/not_this_one_either"
> ALTER SYSTEM
>
> I think this is great, but it would be really helpful to also indicate
> that at this point the server will fail to come back up after a restart. In
> my mind, that's a big part of the reason for having a warning here. Having
> made this mistake a couple of times, I would be able to read between the
> lines, as would many other users, but if you're not familiar with Postgres
> this might still be pretty opaque.


+1

I would at least consider having the UX go something like:

postgres=# ALTER SYSTEM SET shared_preload_libraries = not_such_library;
ERROR: <paraphrase: your system will not reboot in its current state as
that library is not present>.
HINT: to bypass the error please add FORCE before SET
postgres=# ALTER SYSTEM FORCE SET shared_preload_libraries =
no_such_library;
NOTICE: Error suppressed while setting shared_preload_libraries.

That is, have the user express their desire to leave the system in a
precarious state explicitly before actually doing so.

Upon startup, if the system already can track each separate location that
shared_preload_libraries is set, printing out those locations and current
values would be useful context.  Seeing ALTER SYSTEM in that listing would
be helpful.

David J.