org.apache.hadoop.mapreduce

类 Partitioner<KEY,VALUE>

java.lang.Object

org.apache.hadoop.mapreduce.Partitioner<KEY,VALUE>

直接已知子类:

BinaryPartitioner, HashPartitioner, KeyFieldBasedPartitioner, SecondarySort.FirstPartitioner, TotalOrderPartitioner

public abstract class Partitioner<KEY,VALUE>
extends Object

Partitions the key space.

Partitioner controls the partitioning of the keys of the intermediate map-outputs. The key (or a subset of the key) is used to derive the partition, typically by a hash function. The total number of partitions is the same as the number of reduce tasks for the job. Hence this controls which of the m reduce tasks the intermediate key (and hence the record) is sent for reduction.

另请参阅:

Reducer

构造器概要

构造器

构造器和说明
Partitioner()

方法概要

方法

限定符和类型	方法和说明
abstract int	getPartition(KEY key, VALUE value, int numPartitions) Get the partition number for a given key (hence record) given the total number of partitions i.e. number of reduce-tasks for the job.

从类继承的方法 java.lang.Object

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

构造器详细资料

Partitioner

public Partitioner()

方法详细资料

getPartition

public abstract int getPartition(KEY key,
               VALUE value,
               int numPartitions)

Get the partition number for a given key (hence record) given the total number of partitions i.e. number of reduce-tasks for the job.

Typically a hash function on a all or a subset of the key.

参数:

key - the key to be partioned.

value - the entry value.

numPartitions - the total number of partitions.

返回:

the partition number for the key.