org.apache.hadoop.streaming
Class PipeReducer

java.lang.Object
  org.apache.hadoop.streaming.PipeMapRed
      org.apache.hadoop.streaming.PipeReducer

All Implemented Interfaces:

Closeable, JobConfigurable, Reducer

public class PipeReducer
extends PipeMapRed
implements Reducer

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

Author:

Michel Tourn

Field Summary

Fields inherited from class org.apache.hadoop.streaming.PipeMapRed

LOG, mapOutputFieldSeparator, numOfMapOutputKeyFields, numOfMapOutputPartitionFields, numOfReduceOutputKeyFields, outerrThreadsThrowable, reduceOutFieldSeparator

Constructor Summary

PipeReducer()

Method Summary

void	close() Called after the last call to any other method on this object to free and/or flush resources.
void	reduce(WritableComparable key, Iterator values, OutputCollector output, Reporter reporter) Combines values for a given key.

Methods inherited from class org.apache.hadoop.streaming.PipeMapRed

configure, getContext, mapRedFinished

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.mapred.JobConfigurable

configure

Constructor Detail

PipeReducer

public PipeReducer()

Method Detail

reduce

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

Description copied from interface: Reducer

Combines values for a given key. Output values must be of the same type as input values. Input keys must not be altered. Typically all values are combined into zero or one value. Output pairs are collected with calls to OutputCollector.collect(WritableComparable,Writable).

Specified by:

reduce in interface Reducer

Parameters:

key - the key

values - the values to combine

output - to collect combined values

Throws:

IOException

close

public void close()

Description copied from interface: Closeable

Called after the last call to any other method on this object to free and/or flush resources. Typical implementations do nothing.

Specified by:

close in interface Closeable