org.apache.hadoop.mapreduce
Class OutputCommitter

java.lang.Object
  org.apache.hadoop.mapreduce.OutputCommitter

Direct Known Subclasses:

FileOutputCommitter, OutputCommitter

public abstract class OutputCommitter
extends Object

OutputCommitter describes the commit of task output for a Map-Reduce job.

The Map-Reduce framework relies on the OutputCommitter of the job to:

1. Setup the job during initialization. For example, create the temporary output directory for the job during the initialization of the job.
2. Cleanup the job after the job completion. For example, remove the temporary output directory after the job completion.
3. Setup the task temporary output.
4. Check whether a task needs a commit. This is to avoid the commit procedure if a task does not need commit.
5. Commit of the task output.
6. Discard the task commit.

See Also:

FileOutputCommitter, JobContext, TaskAttemptContext

Constructor Summary

OutputCommitter()

Method Summary

abstract void	abortTask(TaskAttemptContext taskContext) Discard the task output
abstract void	cleanupJob(JobContext jobContext) For cleaning up the job's output after job completion
abstract void	commitTask(TaskAttemptContext taskContext) To promote the task's temporary output to final output location The task's output is moved to the job's output directory.
abstract boolean	needsTaskCommit(TaskAttemptContext taskContext) Check whether task needs a commit
abstract void	setupJob(JobContext jobContext) For the framework to setup the job output during initialization
abstract void	setupTask(TaskAttemptContext taskContext) Sets up output for the task.

Methods inherited from class java.lang.Object

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

Constructor Detail

OutputCommitter

public OutputCommitter()

Method Detail

setupJob

public abstract void setupJob(JobContext jobContext)
                       throws IOException

For the framework to setup the job output during initialization

Parameters:

jobContext - Context of the job whose output is being written.

Throws:

IOException - if temporary output could not be created

cleanupJob

public abstract void cleanupJob(JobContext jobContext)
                         throws IOException

For cleaning up the job's output after job completion

Parameters:

jobContext - Context of the job whose output is being written.

Throws:

IOException

setupTask

public abstract void setupTask(TaskAttemptContext taskContext)
                        throws IOException

Sets up output for the task.

Parameters:

taskContext - Context of the task whose output is being written.

Throws:

IOException

needsTaskCommit

public abstract boolean needsTaskCommit(TaskAttemptContext taskContext)
                                 throws IOException

Check whether task needs a commit

Parameters:

taskContext -

Returns:

true/false

Throws:

IOException

commitTask

public abstract void commitTask(TaskAttemptContext taskContext)
                         throws IOException

To promote the task's temporary output to final output location The task's output is moved to the job's output directory.

Parameters:

taskContext - Context of the task whose output is being written.

Throws:

IOException - if commit is not

abortTask

public abstract void abortTask(TaskAttemptContext taskContext)
                        throws IOException

Discard the task output

Parameters:

taskContext -

Throws:

IOException