public double getAverageProbesPerLookup() {
        if (!enablePerfMetrics) {
            throw new IllegalStateException();
        }
        return (1.0 * numProbes) / numKeyLookups;
    }
Returns the average number of probes per key lookup.
indexr-query-opt/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java