Re: Fwd: Identify system databases

Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> writes:
> On Wed, 2025-04-16 at 10:09 +0200, Dominique Devienne wrote:
>> Authentication is cluster-wide, not DB specific, so I'd welcome a way to connect
>> to the cluster, not a specific DB, and introspect shared-objects,
>> including databases
>> I'm allowed to connect to, which could be an empty list.

> It is deep in the DNA of PostgreSQL that you always have to connect to
> a database, unless you establish a replication connection.
> I am surprised that you perceive that as a problem or limitation.

That isn't going to change, and here's why not: a lot of the critical
catalogs are per-database not shared. You aren't going to get
anywhere "introspecting shared objects" when you don't have a copy of
pg_class with which to find the shared catalogs, nor a copy of pg_proc
with which to look up index access method support procedures, etc etc.

You could imagine making up some mini-database that is somehow
forbidden from gaining any user-defined objects and then using
that, but I fail to see why that's a better idea than the
approach we use now. Not being able to use any user-defined
functions or views seems like a pretty huge handicap. And this
hypothetical new mini-database *would* be a special snowflake
in a way that none of the existing ones are, in that the system
would have to prevent actions that are perfectly okay in any
other one. I don't perceive that as a good thing.

(You can, of course, speculate about some major rearchitecting
of the system catalogs that would make this situation different.
I doubt that's going to happen at this point, though. There's
too much stuff that's dependent on how things are now.)

regards, tom lane