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).