Partitioner (Apache Hadoop Main 3.4.1 API) (original) (raw)

• All Superinterfaces:
  JobConfigurable
  All Known Implementing Classes:
  BinaryPartitioner, HashPartitioner, KeyFieldBasedPartitioner, TotalOrderPartitioner

@InterfaceAudience.Public
@InterfaceStability.Stable
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.
Note: A Partitioner is created only when there are multiple reducers.
See Also:
Reducer

• • Method Summary

  All Methods Instance Methods Abstract Methods

  Modifier and Type	Method and Description
  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.

     * ### Methods inherited from interface org.apache.hadoop.mapred.[JobConfigurable](../../../../org/apache/hadoop/mapred/JobConfigurable.html "interface in org.apache.hadoop.mapred")  
     `[configure](../../../../org/apache/hadoop/mapred/JobConfigurable.html#configure-org.apache.hadoop.mapred.JobConf-)`

• • Method Detail

     * #### getPartition  
     int getPartition([K2](../../../../org/apache/hadoop/mapred/Partitioner.html "type parameter in Partitioner") key,  
                      [V2](../../../../org/apache/hadoop/mapred/Partitioner.html "type parameter in Partitioner") 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.  
     Parameters:  
     `key` \- the key to be paritioned.  
     `value` \- the entry value.  
     `numPartitions` \- the total number of partitions.  
     Returns:  
     the partition number for the `key`.