MapReduce v2 (MRv2/YARN) is designed to address which two issues?
The default partitioner computes a hash value for the key and assigns the partition based on this result.
The default Partitioner implementation is called HashPartitioner. It uses the hashCode() method of the key objects modulo the number of partitions total to determine which partition to send a given (key, value) pair to.
In Hadoop, the default partitioner is HashPartitioner, which hashes a record's key to determine which partition (and thus which reducer) the record belongs in.The number of partition is then equal to the number of reduce tasks for the job.
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