@Override
  public Set<String> getAllRpcClients() {
    return this.sessions.keySet().stream()
        .map(IClientSession::toString)
        .collect(Collectors.toSet());
  }
must be called after registerSession()) will mark the session login.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/session/SessionManager.java