public K getKey(Buffer data, int pos, K reuse) {
        return getKey(data, pos);
    }
Returns the sort key for the element at the given index and reuse the input key if possible.
The default implementation ignores the reuse parameter and invokes [[getKey(Buffer, INT]].
If you want to override this method, you must implement [[newKey()]].
indexr-query-opt/src/main/java/org/apache/spark/util/collection/SortDataFormat.java