@Override
  public Map<IDeviceID, IWritableMemChunkGroup> getMemTableMap() {
    return memTableMap;
  }
check whether this memTable has been updated since last timed flush check, update updateTime
when changed
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/memtable/AbstractMemTable.java