MapReduce framework will sort the output of the processing result according to the key value. This default sort can meet part of the needs, but it is also very limited. In our actual needs Demand. For the realization of the secondary sorting, many people have been shared on the Internet, but the analysis of the implementation principle of the secondary sorting and the entire MapReduce framework is still very different, and some analysis has not been verified. This article will tell the implementation of second sorting and the entire processing process of MapReduce through a practical example of a second sort of MapReduce, and verify the correctness of the processing process described by results and the logs of the Map and Reduce.

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