public void updateGaugeValues(double percentile) {
    Snapshot values = histogram.getSnapshot();
    gauges.get(percentile).set(values.getValue(percentile / 100));
  }
Creates a {@link Histogram} metric using {@link ExponentiallyDecayingReservoir}
Keeps a {@link Gauge} for each percentile
samza-api/src/main/java/org/apache/samza/metrics/SamzaHistogram.java