How does MapReduce framework implement the sort phase?

Question

I am interested in the implementation of the MapReduce sort phase; it seems to be very efficient. Could someone provide some references about it please? Thanks!

Answer 1

This points to ReduceTask.java as the place where sort phase is coded. See lines 393-408 in ReduceTask.java. If you need more info, download the entire source and dig into it.

EDITED

"Sort" phase falls under ReduceTask as shown in this figure below from hadoop book. (Page no: 163)