org.apache.hadoop.mapred

接口 Partitioner<K2,V2>

所有超级接口:

JobConfigurable

所有已知实现类:

BinaryPartitioner, HashPartitioner, IndexUpdatePartitioner, KeyFieldBasedPartitioner, SleepJob, TotalOrderPartitioner

public interface Partitioner<K2,V2>
extends JobConfigurable

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

方法概要

方法

限定符和类型	方法和说明
int	getPartition(K2 key, V2 value, int numPartitions) Get the paritition number for a given key (hence record) given the total number of partitions i.e. number of reduce-tasks for the job.

从接口继承的方法 org.apache.hadoop.mapred.JobConfigurable

configure

方法详细资料

getPartition

int getPartition(K2 key,
               V2 value,
               int numPartitions)

Get the paritition 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 paritioned.

value - the entry value.

numPartitions - the total number of partitions.

返回:

the partition number for the key.