@Override
  public void stop() {
    for (DataRegion dataRegion : dataRegionMap.values()) {
      if (dataRegion != null) {
        CompactionScheduleTaskManager.getInstance().unregisterDataRegion(dataRegion);
      }
    }
    syncCloseAllProcessor();
    ThreadUtils.stopThreadPool(
        seqMemtableTimedFlushCheckThread, ThreadName.TIMED_FLUSH_SEQ_MEMTABLE);
    ThreadUtils.stopThreadPool(
        unseqMemtableTimedFlushCheckThread, ThreadName.TIMED_FLUSH_UNSEQ_MEMTABLE);
    if (cachedThreadPool != null) {
      cachedThreadPool.shutdownNow();
    }
    dataRegionMap.clear();
  }
get StorageGroup -> DataRegionIdList map from data/system directory.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/StorageEngine.java