private void updatePeakMemoryUsed() {
        long mem = getTotalMemoryConsumption();
        if (mem > peakMemoryUsedBytes) {
            peakMemoryUsedBytes = mem;
        }
    }
Returns the total amount of memory, in bytes, consumed by this map's managed structures.
indexr-query-opt/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java