org.apache.hadoop.hbase.mapreduce

Class IdentityTableReducer

java.lang.Object

org.apache.hadoop.mapreduce.Reducer<KEYIN,VALUEIN,KEYOUT,Mutation>

org.apache.hadoop.hbase.mapreduce.TableReducer<org.apache.hadoop.io.Writable,Mutation,org.apache.hadoop.io.Writable>

org.apache.hadoop.hbase.mapreduce.IdentityTableReducer

@InterfaceAudience.Public
@InterfaceStability.Stable
public class IdentityTableReducer
extends TableReducer<org.apache.hadoop.io.Writable,Mutation,org.apache.hadoop.io.Writable>

Convenience class that simply writes all values (which must be Put or Delete instances) passed to it out to the configured HBase table. This works in combination with TableOutputFormat which actually does the writing to HBase.

Keys are passed along but ignored in TableOutputFormat. However, they can be used to control how your values will be divided up amongst the specified number of reducers.

You can also use the TableMapReduceUtil class to set up the two classes in one step:

TableMapReduceUtil.initTableReducerJob("table", IdentityTableReducer.class, job);

This will also set the proper TableOutputFormat which is given the table parameter. The Put or Delete define the row and columns implicitly.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.mapreduce.Reducer

org.apache.hadoop.mapreduce.Reducer.Context

Constructor Summary

Constructors

Constructor and Description
IdentityTableReducer()

Method Summary

Methods

Modifier and Type	Method and Description
void	reduce(org.apache.hadoop.io.Writable key, Iterable<Mutation> values, org.apache.hadoop.mapreduce.Reducer.Context context) Writes each given record, consisting of the row key and the given values, to the configured OutputFormat.

Methods inherited from class org.apache.hadoop.mapreduce.Reducer

cleanup, run, setup

Methods inherited from class java.lang.Object

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

Constructor Detail

IdentityTableReducer

public IdentityTableReducer()

Method Detail

reduce

public void reduce(org.apache.hadoop.io.Writable key,
          Iterable<Mutation> values,
          org.apache.hadoop.mapreduce.Reducer.Context context)
            throws IOException,
                   InterruptedException

Writes each given record, consisting of the row key and the given values, to the configured OutputFormat. It is emitting the row key and each Put or Delete as separate pairs.

Overrides:

reduce in class org.apache.hadoop.mapreduce.Reducer<org.apache.hadoop.io.Writable,Mutation,org.apache.hadoop.io.Writable,Mutation>

Parameters:

key - The current row key.

values - The Put or Delete list for the given row.

context - The context of the reduce.

Throws:

IOException - When writing the record fails.

InterruptedException - When the job gets interrupted.