How does MapReduce framework implement the sort phase?

sorting frameworks hadoop mapreduce implementation

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) enter image description here

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