org.apache.hadoop.mapreduce.lib.partition
Class KeyFieldBasedPartitioner<K2,V2>

java.lang.Object
  org.apache.hadoop.mapreduce.Partitioner<K2,V2>
      org.apache.hadoop.mapreduce.lib.partition.KeyFieldBasedPartitioner<K2,V2>

All Implemented Interfaces:

Configurable

@InterfaceAudience.Public
@InterfaceStability.Stable
public class KeyFieldBasedPartitioner<K2,V2>
extends Partitioner<K2,V2>
implements Configurable

Defines a way to partition keys based on certain key fields (also see KeyFieldBasedComparator. The key specification supported is of the form -k pos1[,pos2], where, pos is of the form f[.c][opts], where f is the number of the key field to use, and c is the number of the first character from the beginning of the field. Fields and character posns are numbered starting with 1; a character position of zero in pos2 indicates the field's last character. If '.c' is omitted from pos1, it defaults to 1 (the beginning of the field); if omitted from pos2, it defaults to 0 (the end of the field).

Field Summary

static String

PARTITIONER_OPTIONS

Constructor Summary

KeyFieldBasedPartitioner()

Method Summary

Configuration	getConf() Return the configuration used by this object.
String	getKeyFieldPartitionerOption(JobContext job) Get the KeyFieldBasedPartitioner options
protected int	getPartition(int hash, int numReduceTasks)
int	getPartition(K2 key, V2 value, int numReduceTasks) Get the partition number for a given key (hence record) given the total number of partitions i.e.
protected int	hashCode(byte[] b, int start, int end, int currentHash)
void	setConf(Configuration conf) Set the configuration to be used by this object.
void	setKeyFieldPartitionerOptions(Job job, String keySpec) Set the KeyFieldBasedPartitioner options used for Partitioner

Methods inherited from class java.lang.Object

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

Field Detail

PARTITIONER_OPTIONS

public static String PARTITIONER_OPTIONS

Constructor Detail

KeyFieldBasedPartitioner

public KeyFieldBasedPartitioner()

Method Detail

setConf

public void setConf(Configuration conf)

Description copied from interface: Configurable

Set the configuration to be used by this object.

Specified by:

setConf in interface Configurable

getConf

public Configuration getConf()

Description copied from interface: Configurable

Return the configuration used by this object.

Specified by:

getConf in interface Configurable

getPartition

public int getPartition(K2 key,
                        V2 value,
                        int numReduceTasks)

Description copied from class: Partitioner

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.

Specified by:

getPartition in class Partitioner<K2,V2>

Parameters:

key - the key to be partioned.

value - the entry value.

numReduceTasks - the total number of partitions.

Returns:

the partition number for the key.

hashCode

protected int hashCode(byte[] b,
                       int start,
                       int end,
                       int currentHash)

getPartition

protected int getPartition(int hash,
                           int numReduceTasks)

setKeyFieldPartitionerOptions

public void setKeyFieldPartitionerOptions(Job job,
                                          String keySpec)

Set the KeyFieldBasedPartitioner options used for Partitioner

Parameters:

keySpec - the key specification of the form -k pos1[,pos2], where, pos is of the form f[.c][opts], where f is the number of the key field to use, and c is the number of the first character from the beginning of the field. Fields and character posns are numbered starting with 1; a character position of zero in pos2 indicates the field's last character. If '.c' is omitted from pos1, it defaults to 1 (the beginning of the field); if omitted from pos2, it defaults to 0 (the end of the field).

getKeyFieldPartitionerOption

public String getKeyFieldPartitionerOption(JobContext job)

Get the KeyFieldBasedPartitioner options