org.apache.hadoop.hbase.mapred
Class TableReduce<K extends WritableComparable,V extends Writable>
java.lang.Object
org.apache.hadoop.mapred.MapReduceBase
org.apache.hadoop.hbase.mapred.TableReduce<K,V>
- All Implemented Interfaces:
- Closeable, JobConfigurable, Reducer<K,V,Text,MapWritable>
- Direct Known Subclasses:
- IdentityTableReduce
public abstract class TableReduce<K extends WritableComparable,V extends Writable>
- extends MapReduceBase
- implements Reducer<K,V,Text,MapWritable>
Write a table, sorting by the input key
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
TableReduce
public TableReduce()
initJob
public static void initJob(String table,
Class<? extends TableReduce> reducer,
JobConf job)
- Use this before submitting a TableReduce job. It will
appropriately set up the JobConf.
- Parameters:
table
- reducer
- job
-
reduce
public abstract void reduce(K key,
Iterator<V> values,
OutputCollector<Text,MapWritable> output,
Reporter reporter)
throws IOException
- Description copied from interface:
Reducer
- Reduces values for a given key.
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. Typically all values are combined into zero or one value.
Output pairs are collected with calls to
OutputCollector.collect(WritableComparable,Writable)
.
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).
- Specified by:
reduce
in interface Reducer<K extends WritableComparable,V extends Writable,Text,MapWritable>
- Parameters:
key
- values
- output
- reporter
-
- Throws:
IOException
Copyright © 2006 The Apache Software Foundation