private void loadMqttProps(TrimProperties properties) {
    conf.setMqttDir(properties.getProperty("mqtt_root_dir", conf.getMqttDir()));

    if (properties.getProperty(IoTDBConstant.MQTT_HOST_NAME) != null) {
      conf.setMqttHost(properties.getProperty(IoTDBConstant.MQTT_HOST_NAME).trim());
    } else {
      LOGGER.info("MQTT host is not configured, will use dn_rpc_address.");
      conf.setMqttHost(properties.getProperty(IoTDBConstant.DN_RPC_ADDRESS, conf.getRpcAddress()));
    }

    if (properties.getProperty(IoTDBConstant.MQTT_PORT_NAME) != null) {
      conf.setMqttPort(
          Integer.parseInt(properties.getProperty(IoTDBConstant.MQTT_PORT_NAME).trim()));
    }

    if (properties.getProperty(IoTDBConstant.MQTT_HANDLER_POOL_SIZE_NAME) != null) {
      conf.setMqttHandlerPoolSize(
          Integer.parseInt(
              properties.getProperty(IoTDBConstant.MQTT_HANDLER_POOL_SIZE_NAME).trim()));
    }

    if (properties.getProperty(IoTDBConstant.MQTT_PAYLOAD_FORMATTER_NAME) != null) {
      conf.setMqttPayloadFormatter(
          properties.getProperty(IoTDBConstant.MQTT_PAYLOAD_FORMATTER_NAME).trim());
    }

    if (properties.getProperty(IoTDBConstant.MQTT_DATA_PATH) != null) {
      conf.setMqttDataPath(properties.getProperty(IoTDBConstant.MQTT_DATA_PATH).trim());
    }

    if (properties.getProperty(IoTDBConstant.ENABLE_MQTT) != null) {
      conf.setEnableMQTTService(
          Boolean.parseBoolean(properties.getProperty(IoTDBConstant.ENABLE_MQTT).trim()));
    }

    if (properties.getProperty(IoTDBConstant.MQTT_MAX_MESSAGE_SIZE) != null) {
      conf.setMqttMaxMessageSize(
          Integer.parseInt(properties.getProperty(IoTDBConstant.MQTT_MAX_MESSAGE_SIZE).trim()));
    }
  }
load a property file and set TsfileDBConfig variables.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/conf/IoTDBDescriptor.java