org.apache.hadoop.contrib.index.mapred
Class IndexUpdateReducer

java.lang.Object
  org.apache.hadoop.mapred.MapReduceBase
      org.apache.hadoop.contrib.index.mapred.IndexUpdateReducer

All Implemented Interfaces:

Closeable, JobConfigurable, Reducer<Shard,IntermediateForm,Shard,Text>

public class IndexUpdateReducer
extends MapReduceBase
implements Reducer<Shard,IntermediateForm,Shard,Text>

This reducer applies to a shard the changes for it. A "new version" of a shard is created at the end of a reduce. It is important to note that the new version of the shard is not derived from scratch. By leveraging Lucene's update algorithm, the new version of each Lucene instance will share as many files as possible as the previous version.

Constructor Summary

IndexUpdateReducer()

Method Summary

void	close() Default implementation that does nothing.
void	configure(JobConf job) Default implementation that does nothing.
static Class<? extends WritableComparable>	getOutputKeyClass() Get the reduce output key class.
static Class<? extends Writable>	getOutputValueClass() Get the reduce output value class.
void	reduce(Shard key, Iterator<IntermediateForm> values, OutputCollector<Shard,Text> output, Reporter reporter) Reduces values for a given key.

Methods inherited from class java.lang.Object

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

Constructor Detail

IndexUpdateReducer

public IndexUpdateReducer()

Method Detail

getOutputKeyClass

public static Class<? extends WritableComparable> getOutputKeyClass()

Get the reduce output key class.

Returns:

the reduce output key class

getOutputValueClass

public static Class<? extends Writable> getOutputValueClass()

Get the reduce output value class.

Returns:

the reduce output value class

reduce

public void reduce(Shard key,
                   Iterator<IntermediateForm> values,
                   OutputCollector<Shard,Text> 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. 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).

Specified by:

reduce in interface Reducer<Shard,IntermediateForm,Shard,Text>

Parameters:

key - the key.

values - the list of values to reduce.

output - to collect keys and combined values.

reporter - facility to report progress.

Throws:

IOException

configure

public void configure(JobConf job)

Description copied from class: MapReduceBase

Default implementation that does nothing.

Specified by:

configure in interface JobConfigurable

Overrides:

configure in class MapReduceBase

Parameters:

job - the configuration

close

public void close()
           throws IOException

Description copied from class: MapReduceBase

Default implementation that does nothing.

Specified by:

close in interface Closeable

Overrides:

close in class MapReduceBase

Throws:

IOException