private void timedFlushSeqMemTable() {
    for (DataRegion dataRegion : dataRegionMap.values()) {
      if (dataRegion != null) {
        dataRegion.timedFlushSeqMemTable();
      }
    }
  }
get StorageGroup -> DataRegionIdList map from data/system directory.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/StorageEngine.java