How does HashPartitioner work?

Question

I read up on the documentation of HashPartitioner. Unfortunately nothing much was explained except for the API calls. I am under the assumption that HashPartitioner

Answer 1

The HashPartitioner.getPartition method takes a key as its argument and returns the index of the partition which the key belongs to. The partitioner has to know what the valid indices are, so it returns numbers in the right range. The number of partitions is specified through the numPartitions constructor argument.

The implementation returns roughly key.hashCode() % numPartitions. See Partitioner.scala for more details.