code: private void sendPipelineCheckMaster() throws IOException {
      if (urlParser.getHaMode() == HaMode.AURORA) {
        writer.startPacket(0);
        writer.write(COM_QUERY);
        writer.write(IS_MASTER_QUERY);
        writer.flush();
      }
    }
docs: Send query to identify if server is master.
  
  @throws IOException in case of socket error.