MapReduce - Partition


Partitioner partitions the key space from the map-outputs to be sent to the reducer.

The total number of partitions is the same as the number of reduce tasks for the job

It controls which of the m reduce tasks the intermediate key (and hence the record) is sent to for reduction.


The key (or a subset of the key) is used to derive the partition, typically by a hash function. See default



HashPartitioner is the default Partitioner.

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