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.
