@Override
    public synchronized GcData clone() {
      try {
        return (GcData) super.clone();
      } catch (CloneNotSupportedException e) {
        throw new RuntimeException(e);
      }
    }
Returns the percentage (0..100) of time that the JVM spent in GC pauses
within the observation window of the associated GcTimeMonitor.
common/src/java/org/apache/hadoop/hive/common/GcTimeMonitor.java