org.apache.hadoop.streaming

类 PipeReducer

java.lang.Object

org.apache.hadoop.streaming.PipeMapRed

org.apache.hadoop.streaming.PipeReducer

所有已实现的接口:

Closeable, AutoCloseable, JobConfigurable, Reducer

直接已知子类:

PipeCombiner

public class PipeReducer
extends PipeMapRed
implements Reducer

A generic Reducer bridge. It delegates operations to an external program via stdin and stdout.

字段概要

从类继承的字段 org.apache.hadoop.streaming.PipeMapRed

LOG, outerrThreadsThrowable

构造器概要

构造器

构造器和说明
PipeReducer()

方法概要

方法

限定符和类型	方法和说明
void	close()
void	configure(JobConf job) Initializes a new instance from a JobConf.
byte[]	getFieldSeparator() Returns the field separator to be used.
byte[]	getInputSeparator() Returns the input separator to be used.
int	getNumOfKeyFields() Returns the number of key fields.
void	reduce(Object key, Iterator values, OutputCollector output, Reporter reporter) Reduces values for a given key.

从类继承的方法 org.apache.hadoop.streaming.PipeMapRed

getClientInput, getClientOutput, getConfiguration, getContext, mapRedFinished

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

PipeReducer

public PipeReducer()

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

覆盖:

configure 在类中 PipeMapRed

参数:

job - the configuration

reduce

public void reduce(Object key,
          Iterator values,
          OutputCollector output,
          Reporter reporter)
            throws IOException

从接口复制的说明: Reducer

Reduces values for a given key.

The framework calls this method for each <key, (list of values)> pair in the grouped inputs. Output values must be of the same type as input values. Input keys must not be altered. The framework will reuse the key and value objects that are passed into the reduce, therefore the application should clone the objects they want to keep a copy of. In many cases, all values are combined into zero or one value.

Output pairs are collected with calls to OutputCollector.collect(Object,Object).

Applications can use the Reporter provided to report progress or just indicate that they are alive. In scenarios where the application takes an insignificant amount of time to process individual key/value pairs, this is crucial since the framework might assume that the task has timed-out and kill that task. The other way of avoiding this is to set mapred.task.timeout to a high-enough value (or even zero for no time-outs).

指定者:

reduce 在接口中 Reducer

参数:

key - the key.

values - the list of values to reduce.

output - to collect keys and combined values.

reporter - facility to report progress.

抛出:

IOException

close

public void close()

指定者:

close 在接口中 Closeable

指定者:

close 在接口中 AutoCloseable

getInputSeparator

public byte[] getInputSeparator()

从类复制的说明: PipeMapRed

Returns the input separator to be used.

指定者:

getInputSeparator 在类中 PipeMapRed

getFieldSeparator

public byte[] getFieldSeparator()

从类复制的说明: PipeMapRed

Returns the field separator to be used.

指定者:

getFieldSeparator 在类中 PipeMapRed

getNumOfKeyFields

public int getNumOfKeyFields()

从类复制的说明: PipeMapRed

Returns the number of key fields.

指定者:

getNumOfKeyFields 在类中 PipeMapRed