admit

Admits server, which reported identifier, if that is the cluster this catalog belongs to - which the first server admitted decides.

The catalog maps types by OID, and only a physical standby is sure to have its primary's: it replays the primary's WAL, and PostgreSQL will not stream to a standby whose system identifier differs. So the identifier tells a server this catalog describes from one it would mistranslate - a logical replica, another node of a multi-master set, an unrelated server listed by mistake.

Runs under lock, so the first two servers asked cannot both decide.