| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.hadoop.mapreduce.lib.chain; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.hadoop.conf.Configuration; |
| import org.apache.hadoop.mapreduce.Job; |
| import org.apache.hadoop.mapreduce.Mapper; |
| import org.apache.hadoop.mapreduce.Reducer; |
| import org.apache.hadoop.mapreduce.lib.chain.Chain.ChainBlockingQueue; |
| |
| import java.io.IOException; |
| |
| /** |
| * The ChainReducer class allows to chain multiple Mapper classes after a |
| * Reducer within the Reducer task. |
| * |
| * <p> |
| * For each record output by the Reducer, the Mapper classes are invoked in a |
| * chained (or piped) fashion. The output of the reducer becomes the input of |
| * the first mapper and output of first becomes the input of the second, and so |
| * on until the last Mapper, the output of the last Mapper will be written to |
| * the task's output. |
| * </p> |
| * <p> |
| * The key functionality of this feature is that the Mappers in the chain do not |
| * need to be aware that they are executed after the Reducer or in a chain. This |
| * enables having reusable specialized Mappers that can be combined to perform |
| * composite operations within a single task. |
| * </p> |
| * <p> |
| * Special care has to be taken when creating chains that the key/values output |
| * by a Mapper are valid for the following Mapper in the chain. It is assumed |
| * all Mappers and the Reduce in the chain use matching output and input key and |
| * value classes as no conversion is done by the chaining code. |
| * </p> |
| * </p> Using the ChainMapper and the ChainReducer classes is possible to |
| * compose Map/Reduce jobs that look like <code>[MAP+ / REDUCE MAP*]</code>. And |
| * immediate benefit of this pattern is a dramatic reduction in disk IO. </p> |
| * <p> |
| * IMPORTANT: There is no need to specify the output key/value classes for the |
| * ChainReducer, this is done by the setReducer or the addMapper for the last |
| * element in the chain. |
| * </p> |
| * ChainReducer usage pattern: |
| * <p/> |
| * |
| * <pre> |
| * ... |
| * Job = new Job(conf); |
| * .... |
| * <p/> |
| * Configuration reduceConf = new Configuration(false); |
| * ... |
| * ChainReducer.setReducer(job, XReduce.class, LongWritable.class, Text.class, |
| * Text.class, Text.class, true, reduceConf); |
| * <p/> |
| * ChainReducer.addMapper(job, CMap.class, Text.class, Text.class, |
| * LongWritable.class, Text.class, false, null); |
| * <p/> |
| * ChainReducer.addMapper(job, DMap.class, LongWritable.class, Text.class, |
| * LongWritable.class, LongWritable.class, true, null); |
| * <p/> |
| * ... |
| * <p/> |
| * job.waitForCompletion(true); |
| * ... |
| * </pre> |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public class ChainReducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT> extends |
| Reducer<KEYIN, VALUEIN, KEYOUT, VALUEOUT> { |
| |
| /** |
| * Sets the {@link Reducer} class to the chain job. |
| * |
| * <p> |
| * The key and values are passed from one element of the chain to the next, by |
| * value. For the added Reducer the configuration given for it, |
| * <code>reducerConf</code>, have precedence over the job's Configuration. |
| * This precedence is in effect when the task is running. |
| * </p> |
| * <p> |
| * IMPORTANT: There is no need to specify the output key/value classes for the |
| * ChainReducer, this is done by the setReducer or the addMapper for the last |
| * element in the chain. |
| * </p> |
| * |
| * @param job |
| * the job |
| * @param klass |
| * the Reducer class to add. |
| * @param inputKeyClass |
| * reducer input key class. |
| * @param inputValueClass |
| * reducer input value class. |
| * @param outputKeyClass |
| * reducer output key class. |
| * @param outputValueClass |
| * reducer output value class. |
| * @param reducerConf |
| * a configuration for the Reducer class. It is recommended to use a |
| * Configuration without default values using the |
| * <code>Configuration(boolean loadDefaults)</code> constructor with |
| * FALSE. |
| */ |
| public static void setReducer(Job job, Class<? extends Reducer> klass, |
| Class<?> inputKeyClass, Class<?> inputValueClass, |
| Class<?> outputKeyClass, Class<?> outputValueClass, |
| Configuration reducerConf) { |
| job.setReducerClass(ChainReducer.class); |
| job.setOutputKeyClass(outputKeyClass); |
| job.setOutputValueClass(outputValueClass); |
| Chain.setReducer(job, klass, inputKeyClass, inputValueClass, |
| outputKeyClass, outputValueClass, reducerConf); |
| } |
| |
| /** |
| * Adds a {@link Mapper} class to the chain reducer. |
| * |
| * <p> |
| * The key and values are passed from one element of the chain to the next, by |
| * value For the added Mapper the configuration given for it, |
| * <code>mapperConf</code>, have precedence over the job's Configuration. This |
| * precedence is in effect when the task is running. |
| * </p> |
| * <p> |
| * IMPORTANT: There is no need to specify the output key/value classes for the |
| * ChainMapper, this is done by the addMapper for the last mapper in the |
| * chain. |
| * </p> |
| * |
| * @param job |
| * The job. |
| * @param klass |
| * the Mapper class to add. |
| * @param inputKeyClass |
| * mapper input key class. |
| * @param inputValueClass |
| * mapper input value class. |
| * @param outputKeyClass |
| * mapper output key class. |
| * @param outputValueClass |
| * mapper output value class. |
| * @param mapperConf |
| * a configuration for the Mapper class. It is recommended to use a |
| * Configuration without default values using the |
| * <code>Configuration(boolean loadDefaults)</code> constructor with |
| * FALSE. |
| */ |
| public static void addMapper(Job job, Class<? extends Mapper> klass, |
| Class<?> inputKeyClass, Class<?> inputValueClass, |
| Class<?> outputKeyClass, Class<?> outputValueClass, |
| Configuration mapperConf) throws IOException { |
| job.setOutputKeyClass(outputKeyClass); |
| job.setOutputValueClass(outputValueClass); |
| Chain.addMapper(false, job, klass, inputKeyClass, inputValueClass, |
| outputKeyClass, outputValueClass, mapperConf); |
| } |
| |
| private Chain chain; |
| |
| protected void setup(Context context) { |
| chain = new Chain(false); |
| chain.setup(context.getConfiguration()); |
| } |
| |
| public void run(Context context) throws IOException, InterruptedException { |
| setup(context); |
| |
| // if no reducer is set, just do nothing |
| if (chain.getReducer() == null) { |
| return; |
| } |
| int numMappers = chain.getAllMappers().size(); |
| // if there are no mappers in chain, run the reducer |
| if (numMappers == 0) { |
| chain.runReducer(context); |
| return; |
| } |
| |
| // add reducer and all mappers with proper context |
| ChainBlockingQueue<Chain.KeyValuePair<?, ?>> inputqueue; |
| ChainBlockingQueue<Chain.KeyValuePair<?, ?>> outputqueue; |
| // add reducer |
| outputqueue = chain.createBlockingQueue(); |
| chain.addReducer(context, outputqueue); |
| // add all mappers except last one |
| for (int i = 0; i < numMappers - 1; i++) { |
| inputqueue = outputqueue; |
| outputqueue = chain.createBlockingQueue(); |
| chain.addMapper(inputqueue, outputqueue, context, i); |
| } |
| // add last mapper |
| chain.addMapper(outputqueue, context, numMappers - 1); |
| |
| // start all threads |
| chain.startAllThreads(); |
| |
| // wait for all threads |
| chain.joinAllThreads(); |
| } |
| } |