@InterfaceAudience.Private
  public MutableRate newRate(String name, String desc, boolean extended, boolean returnExisting) {
    if (returnExisting) {
      MutableMetric rate = metricsMap.get(name);
      if (rate != null) {
        if (rate instanceof MutableRate) {
          return (MutableRate) rate;
        }

        throw new MetricsException("Unexpected metrics type " + rate.getClass() + " for " + name);
      }
    }
    MutableRate ret = new MutableRate(name, desc, extended);
    return addNewMetricIfAbsent(name, ret, MutableRate.class);
  }
Create a mutable rate metric (for throughput measurement)
@param name     of the metric
@param desc     description
@param extended produce extended stat (stdev/min/max etc.) if true
@return a new mutable rate metric object
hbase-hadoop-compat/src/main/java/org/apache/hadoop/metrics2/lib/DynamicMetricsRegistry.java