pg_auth_members
   The catalog pg_auth_members shows the membership
   relations between roles.  Any non-circular set of relationships is allowed.
  
   Because user identities are cluster-wide,
   pg_auth_members
   is shared across all databases of a cluster: there is only one
   copy of pg_auth_members per cluster, not
   one per database.
  
Table 52.9. pg_auth_members Columns