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 43-9. pg_auth_members Columns
| Name | Type | References | Description | 
|---|
| roleid | oid | pg_authid.oid | ID of a role that has a member | 
| member | oid | pg_authid.oid | ID of a role that is a member of roleid | 
| grantor | oid | pg_authid.oid | ID of the role that granted this membership | 
| admin_option | bool |  | True if member may grant membership in
       roleid to others |