public MetricSnapshot createSnapshot() {
        Map<MetricDimensions, MetricSet> newData = new HashMap<>();
        for (Map.Entry<MetricDimensions, MetricSet> entry : data.entrySet()) {
            MetricSet newSet = entry.getValue().partialClone();
            if ( ! newSet.isEmpty()) {
                newData.put(entry.getKey(), newSet);
            }
        }
        return createWithMetrics(newData);
    }
Create a new snapshot instance where Gauge metrics are preserved
with the last-values they have in this snapshot instance.
container-core/src/main/java/com/yahoo/container/jdisc/state/MetricSnapshot.java