public void clearMaskOfStation(String stationName) {
   StationMeta stationMeta = getStationMeta(stationName, false);
   if (stationMeta == null) {
     // log.warn("station not found "+stationName);
     return;
   }
   BTreeMap<String, TimeSeriesMask> maskMap =
       db.getTreeMap(stationMeta.db_name_sensor_time_series_mask_map);
   maskMap.clear();
 }
  /** delete all content in db */
  public void clear() {
    for (StationMeta stationMeta : stationMetaMap.values()) {
      BTreeMap<String, SensorMeta> sensorMap = getSensorMap(stationMeta);
      for (SensorMeta sensorMeta : sensorMap.values()) {
        /*BTreeMap<Integer, ChunkMeta> chunkMetaMap = getSensorChunkMetaMap(sensorMeta);
        chunkMetaMap.clear();
        BTreeMap<Integer, Chunk> chunkMap = getSensorChunkMap(sensorMeta);
        chunkMap.clear();*/
        db.delete(sensorMeta.db_name_sensor_chunkmeta_map);
        db.delete(sensorMeta.db_name_sensor_chunk_map);
      }
      // sensorMap.clear();
      db.delete(stationMeta.db_name_sensor_map);

      db.delete(stationMeta.db_name_sensor_time_series_mask_map);
    }
    stationMetaMap.clear();
    commit();
    compact();
  }