Tom Lane wrote:
> Andrew Dunstan <andrew@dunslane.net> writes:
> > On 03/11/2014 09:37 PM, Tom Lane wrote:
> >> In particular, I'd like to see an exclusion that prevents local users
> >> from having the same name as any global user, so that we don't have
> >> ambiguity in GRANT and similar commands. This doesn't seem simple to
> >> enforce (if we supported partial indexes on system catalogs, it would
> >> be ...) but surely this representation is more amenable to enforcing it
> >> than the existing one.
>
> > Should be workable if you're creating a local name - just check against
> > the list of global roles.
>
> Concurrent creations won't be safe without some sort of locking scheme.
> A unique index would be a lot better way of plugging that hole than a
> system-wide lock on user creation. But not sure how to define a unique
> index that allows (joe, db1) to coexist with (joe, db2) but not with
> (joe, 0).
Isn't this just a case of creating a suitable operator and an exclusion
constraint? Defining the constraint in BKI might require extra
infrastructure, but it should be possible.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services