private boolean loadCompactionSubTaskCountHotModifiedProps(TrimProperties properties)
      throws IOException {
    int newConfigSubtaskNum =
        Integer.parseInt(
            properties.getProperty(
                "sub_compaction_thread_count",
                ConfigurationFileUtils.getConfigurationDefaultValue(
                    "sub_compaction_thread_count")));
    if (newConfigSubtaskNum <= 0) {
      newConfigSubtaskNum = 1;
    }
    if (newConfigSubtaskNum == conf.getSubCompactionTaskNum()) {
      return false;
    }
    conf.setSubCompactionTaskNum(newConfigSubtaskNum);
    return true;
  }
load a property file and set TsfileDBConfig variables.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/conf/IoTDBDescriptor.java