private String getWalThrottleThreshold(TrimProperties prop) throws IOException {
    String old_throttleThreshold = prop.getProperty(DEFAULT_WAL_THRESHOLD_NAME[0], null);
    if (old_throttleThreshold != null) {
      LOGGER.warn(
          "The throttle threshold params: {} is deprecated, please use {}",
          DEFAULT_WAL_THRESHOLD_NAME[0],
          DEFAULT_WAL_THRESHOLD_NAME[1]);
      return old_throttleThreshold;
    }
    return prop.getProperty(
        DEFAULT_WAL_THRESHOLD_NAME[1],
        ConfigurationFileUtils.getConfigurationDefaultValue(DEFAULT_WAL_THRESHOLD_NAME[1]));
  }
load a property file and set TsfileDBConfig variables.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/conf/IoTDBDescriptor.java