Package org.apache.hadoop.mapreduce.lib.partition

Class RehashPartitioner<K,V>

java.lang.Object

org.apache.hadoop.mapreduce.Partitioner<K,V>

org.apache.hadoop.mapreduce.lib.partition.RehashPartitioner<K,V>

@Public
@Stable
public class RehashPartitioner<K,V>
extends Partitioner<K,V>

This partitioner rehashes values returned by Object.hashCode() to get smoother distribution between partitions which may improve reduce reduce time in some cases and should harm things in no cases. This partitioner is suggested with Integer and Long keys with simple patterns in their distributions.

Since:

2.0.3

Constructor Summary

Constructors

Constructor	Description
RehashPartitioner()

Method Summary

Modifier and Type	Method	Description
int	getPartition(K key, V value, int numReduceTasks)	Rehash Object.hashCode() to partition.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

RehashPartitioner

public RehashPartitioner()

Method Details

getPartition

public int getPartition(K key,
 V value,
 int numReduceTasks)

Rehash Object.hashCode() to partition.

Specified by:

getPartition in class Partitioner<K,V>

Parameters:

key - the key to be partioned.

value - the entry value.

numReduceTasks - the total number of partitions.

Returns:

the partition number for the key.