code: def session_info(self, session):
          
          _, sp_hkey = self._keygen(session)
          picked_event = self.r.hgetall(sp_hkey)
          event = {s(k): pickle.loads(v) for k, v in picked_event.items()}
          return event
docs: Return all session unique ids recorded in prepare phase.
  
          :param ts: timestamp, default to current timestamp
          :return: set of session unique ids