@Override
  public double getCompactionPressure() {
    double max = 0;
    for (Region region : onlineRegions.values()) {
      for (Store store : region.getStores()) {
        double normCount = store.getCompactionPressure();
        if (normCount > max) {
          max = normCount;
        }
      }
    }
    return max;
  }
May be null if this is a master which not carry table.
@return The cache for mob files used by the regionserver.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java