public <T> Gauge<T> newGauge(String name, T value) {
    return registry.newGauge(groupName, new Gauge<T>((prefix + name).toLowerCase(), value));
  }
MetricGroup is a little helper class to make it easy to register and
manage a group of counters, gauges and timers.  It's shared between Java
and Scala
samza-core/src/main/java/org/apache/samza/metrics/MetricGroup.java