@Override
  public synchronized void snapshot(MetricsRecordBuilder metricsRecordBuilder, boolean all) {
    snapshot(name, desc, histogram, metricsRecordBuilder, all);
  }
A histogram implementation that runs in constant space, and exports to hadoop2's metrics2 system.
hbase-hadoop-compat/src/main/java/org/apache/hadoop/metrics2/lib/MutableHistogram.java