synchronized public Map<MetricQuantile, Long> snapshot() throws IOException {
    // flush the buffer first for best results
    insertBatch();
    Map<MetricQuantile, Long> values = new HashMap<>(quantiles.length);
    for (int i = 0; i < quantiles.length; i++) {
      values.put(quantiles[i], query(quantiles[i].quantile));
    }

    return values;
  }
Get a snapshot of the current values of all the tracked quantiles.
@return snapshot of the tracked quantiles if no items have been added to the estimator
hbase-hadoop-compat/src/main/java/org/apache/hadoop/metrics2/util/MetricSampleQuantiles.java