org.apache.hadoop.mapred.lib

类 KeyFieldBasedPartitioner<K2,V2>

java.lang.Object

org.apache.hadoop.mapred.lib.KeyFieldBasedPartitioner<K2,V2>

所有已实现的接口:

JobConfigurable, Partitioner<K2,V2>

public class KeyFieldBasedPartitioner<K2,V2>
extends Object
implements Partitioner<K2,V2>

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).

构造器概要

构造器

构造器和说明
KeyFieldBasedPartitioner()

方法概要

方法

限定符和类型	方法和说明
void	configure(JobConf job) Initializes a new instance from a JobConf.
protected int	getPartition(int hash, int numReduceTasks)
int	getPartition(K2 key, V2 value, int numReduceTasks) 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.
protected int	hashCode(byte[] b, int start, int end, int currentHash)

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

KeyFieldBasedPartitioner

public KeyFieldBasedPartitioner()

方法详细资料

configure

public void configure(JobConf job)

从接口复制的说明: JobConfigurable

Initializes a new instance from a JobConf.

指定者:

configure 在接口中 JobConfigurable

参数:

job - the configuration

getPartition

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

从接口复制的说明: Partitioner

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.

指定者:

getPartition 在接口中 Partitioner<K2,V2>

参数:

key - the key to be paritioned.

value - the entry value.

numReduceTasks - the total number of partitions.

返回:

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)