@Override
    public String toString() {
        return "Rate(" +
            "unit=" + unit +
            ", stat=" + stat +
            ')';
    }
The rate of the given quantity. By default this is the total observed over a set of samples from a sampled statistic
divided by the elapsed time over the sample windows. Alternative {@link SampledStat} implementations can be provided,
however, to record the rate of occurrences (e.g. the count of values measured over the time interval) or other such
values.
clients/src/main/java/org/apache/kafka/common/metrics/stats/Rate.java