Unambiguous identification of the cluster.

Hey all,

Is there are way to uniquely identify the cluster?
May be some identificator such as UUID?

PS.
I need to unambiguous identify the database.
There are current_catalog (and current_database())
function. There are also inet_server_addr() and
inet_server_port() functions, but these functions
returns NULL if the connection established via
socket. On the other hand, the server may be
configured to listen some port (not 5432) and
interface and if the connection established via
TCP/IP, these functions will returns non-NULL
values. So, it is not convenient (or even not
possible?) to unambiguous identify the cluster
on the client side (without knowledge about
default port and inteface which are listened
by particular Postgres server).

Any ideas?

--
// Dmitriy.