private void updatePeakMemoryUsed() {
        long mem = getMemoryUsage();
        if (mem > peakMemoryUsedBytes) {
            peakMemoryUsedBytes = mem;
        }
    }
Return the total memory usage of this sorter, including the data pages and the sorter's pointer
array.
indexr-query-opt/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java