public class PipeReducer extends PipeMapRed implements Reducer
LOG, outerrThreadsThrowable
Constructor and Description |
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PipeReducer() |
Modifier and Type | Method and Description |
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void |
close() |
void |
configure(JobConf job)
Initializes a new instance from a
JobConf . |
void |
reduce(Object key,
Iterator values,
OutputCollector output,
Reporter reporter)
Reduces values for a given key.
|
getContext, mapRedFinished
public void configure(JobConf job)
JobConfigurable
JobConf
.configure
in interface JobConfigurable
configure
in class PipeMapRed
job
- the configurationpublic void reduce(Object key, Iterator values, OutputCollector output, Reporter reporter) throws IOException
Reducer
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).
reduce
in interface Reducer
key
- the key.values
- the list of values to reduce.output
- to collect keys and combined values.reporter
- facility to report progress.IOException
public void close()
close
in interface Closeable
close
in interface AutoCloseable
Copyright © 2010 The Apache Software Foundation