@Override
    public RecordPointerAndKeyPrefix getKey(LongArray data, int pos, RecordPointerAndKeyPrefix reuse) {
        reuse.recordPointer = data.get(pos * 2);
        reuse.keyPrefix = data.get(pos * 2 + 1);
        return reuse;
    }
Supports sorting an array of (record pointer, key prefix) pairs.
Used in {@link UnsafeInMemorySorter}.

Within each long[] buffer, position {@code 2 * i} holds a pointer pointer to the record at
index {@code i}, while position {@code 2 * i + 1} in the array holds an 8-byte key prefix.
indexr-query-opt/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSortDataFormat.java