@Override
  public void decGauge(String gaugeName, long delta) {
    MutableGaugeLong gaugeInt = metricsRegistry.getGauge(gaugeName, 0L);
    gaugeInt.decr(delta);
  }
Decrease the value of a named gauge.
@param gaugeName The name of the gauge.
@param delta     the ammount to subtract from a gauge value.
hbase-hadoop-compat/src/main/java/org/apache/hadoop/hbase/metrics/BaseSourceImpl.java