org.apache.hadoop.mapred

Class ReduceTask

java.lang.Object

org.apache.hadoop.mapred.Task

org.apache.hadoop.mapred.ReduceTask

All Implemented Interfaces:

Configurable, Writable

@InterfaceAudience.Private
@InterfaceStability.Unstable
public class ReduceTask
extends Task

A Reduce task.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.mapred.Task

Task.CombineOutputCollector<K,V>, Task.CombinerRunner<K,V>, Task.CombineValuesIterator<KEY,VALUE>, Task.Counter, Task.NewCombinerRunner<K,V>, Task.OldCombinerRunner<K,V>, Task.TaskReporter

Field Summary

Fields inherited from class org.apache.hadoop.mapred.Task

committer, conf, DEFAULT_COMBINE_RECORDS_BEFORE_PROGRESS, extraData, failedShuffleCounter, FILESYSTEM_COUNTER_GROUP, gcUpdater, jobCleanup, jobContext, jobRunStateForCleanup, jobSetup, lDirAlloc, mapOutputFile, MERGED_OUTPUT_PREFIX, mergedMapOutputsCounter, outputFormat, PROGRESS_INTERVAL, shuffleSecret, spilledRecordsCounter, taskCleanup, taskContext, tokenSecret, umbilical

Constructor Summary

Constructors

Constructor and Description
ReduceTask()
ReduceTask(String jobFile, TaskAttemptID taskId, int partition, int numMaps, int numSlotsRequired)

Method Summary

Methods

Modifier and Type	Method and Description
int	getNumMaps()
boolean	isMapTask()
void	localizeConfiguration(JobConf conf) Localize the given JobConf to be specific for this task.
void	readFields(DataInput in) Deserialize the fields of this object from in.
void	run(JobConf job, TaskUmbilicalProtocol umbilical) Run this task as a part of the named job.
void	write(DataOutput out) Serialize the fields of this object to out.

Methods inherited from class org.apache.hadoop.mapred.Task

createReduceContext, done, getConf, getFileSystemCounterNames, getFsStatistics, getJobFile, getJobID, getJobTokenSecret, getMapOutputFile, getNumSlotsRequired, getPartition, getPhase, getProgress, getShuffleSecret, getSkipRanges, getTaskID, initialize, isSkipping, keepTaskFiles, normalizeStatus, reportFatalError, reportNextRecordRange, runJobCleanupTask, runJobSetupTask, runTaskCleanupTask, setConf, setJobFile, setJobTokenSecret, setPhase, setShuffleSecret, setSkipping, setSkipRanges, setWriteSkipRecs, statusUpdate, toString, toWriteSkipRecs

Methods inherited from class java.lang.Object

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

Constructor Detail

ReduceTask

public ReduceTask()

ReduceTask

public ReduceTask(String jobFile,
          TaskAttemptID taskId,
          int partition,
          int numMaps,
          int numSlotsRequired)

Method Detail

isMapTask

public boolean isMapTask()

Specified by:

isMapTask in class Task

getNumMaps

public int getNumMaps()

localizeConfiguration

public void localizeConfiguration(JobConf conf)
                           throws IOException

Localize the given JobConf to be specific for this task.

Overrides:

localizeConfiguration in class Task

Throws:

IOException

write

public void write(DataOutput out)
           throws IOException

Description copied from interface: Writable

Serialize the fields of this object to out.

Specified by:

write in interface Writable

Overrides:

write in class Task

Parameters:

out - DataOuput to serialize this object into.

Throws:

IOException

readFields

public void readFields(DataInput in)
                throws IOException

Description copied from interface: Writable

Deserialize the fields of this object from in.

For efficiency, implementations should attempt to re-use storage in the existing object where possible.

Specified by:

readFields in interface Writable

Overrides:

readFields in class Task

Parameters:

in - DataInput to deseriablize this object from.

Throws:

IOException

run

public void run(JobConf job,
       TaskUmbilicalProtocol umbilical)
         throws IOException,
                InterruptedException,
                ClassNotFoundException

Description copied from class: Task

Run this task as a part of the named job. This method is executed in the child process and is what invokes user-supplied map, reduce, etc. methods.

Specified by:

run in class Task

umbilical - for progress reports

Throws:

IOException

InterruptedException

ClassNotFoundException