OptimizedDataJoinReducerBase.java

/**
 * 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 hip.ch6.joins.repartition.impl;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * This abstract class serves as the base class for the reducer class of a data
 * join job. The reduce function will first group the values according to their
 * input tags, and then compute the cross product of over the groups. For each
 * tuple in the cross product, it calls the following method, which is expected
 * to be implemented in a subclass.
 * <p/>
 * protected abstract OptimizedTaggedMapOutput combine(String key, OptimizedTaggedMapOutput value1, OptimizedTaggedMapOutput value2);
 * <p/>
 * The above method is expected to produce one output value from an array of
 * records of different sources. The user code can also perform filtering here.
 * It can return null if it decides to the records do not meet certain
 * conditions.
 */
public abstract class OptimizedDataJoinReducerBase
    extends OptimizedJobBase {

  protected Reporter reporter = null;

  private long maxNumOfValuesPerGroup = 100;

  protected long largestNumOfValues = 0;

  protected long numOfValues = 0;

  protected long collected = 0;

  protected JobConf job;

  public void close() throws IOException {
    if (this.reporter != null) {
      this.reporter.setStatus(super.getReport());
    }
  }

  public void configure(JobConf job) {
    super.configure(job);
    this.job = job;
    this.maxNumOfValuesPerGroup =
        job.getLong("datajoin.maxNumOfValuesPerGroup", 100);
  }


  public void reduce(Object key, Iterator values,
                     OutputCollector output, Reporter reporter)
      throws IOException {
    if (this.reporter == null) {
      this.reporter = reporter;
    }

    CompositeKey k = (CompositeKey) key;

    System.out.println("K[" + k + "]");

    List<OutputValue> smaller =
        new ArrayList<OutputValue>();
    this.numOfValues = 0;

    while (values.hasNext()) {
      numOfValues++;

      Object value = values.next();

      System.out.println("  V[" + value + "]");

      if (this.numOfValues % 100 == 0) {
        reporter.setStatus("key: " + key.toString() + " numOfValues: "
            + this.numOfValues);
      }

      if (this.numOfValues > this.maxNumOfValuesPerGroup) {
        continue;
      }

      OutputValue cloned =
          ((OutputValue) value).clone(job);

      if (cloned.isSmaller().get()) {
        System.out.println("Adding to smaller coll");
        smaller.add(cloned);
      } else {
        System.out.println("Join/collect");
        joinAndCollect(k, smaller, cloned, output, reporter);
      }
    }

    if (this.numOfValues > this.largestNumOfValues) {
      this.largestNumOfValues = numOfValues;
      LOG.info("key: " + key.toString() + " this.largestNumOfValues: "
          + this.largestNumOfValues);
    }

    addLongValue("groupCount", 1);
  }

  /**
   * Join the list of the value lists, and collect the results.
   *
   * @param key
   * @param smaller
   * @param value
   * @param output
   * @param reporter
   * @throws java.io.IOException
   */
  private void joinAndCollect(CompositeKey key,
                              List<OutputValue> smaller,
                              OutputValue value,
                              OutputCollector output,
                              Reporter reporter)
      throws IOException {
    if (smaller.size() < 1) {
      OutputValue combined =
          combine(key.getKey(), null, value);
      collect(key, combined, output, reporter);
    } else {
      for (OutputValue small : smaller) {
        OutputValue combined =
            combine(key.getKey(), small, value);
        collect(key, combined, output, reporter);
      }
    }
  }

  private static Text outputKey = new Text();

  private void collect(CompositeKey key,
                       OutputValue combined,
                       OutputCollector output,
                       Reporter reporter) throws IOException {
    this.collected += 1;
    addLongValue("collectedCount", 1);
    if (combined != null) {
      outputKey.set(key.getKey());
      output.collect(outputKey, combined.getData());
      reporter.setStatus(
          "key: " + key.toString() + " collected: " + collected);
      addLongValue("actuallyCollectedCount", 1);
    }

  }

  /**
   * @param key
   * @param smallValue
   * @param largeValue
   * @return combined value derived from values of the sources
   */
  protected abstract OutputValue combine(String key,
                                         OutputValue smallValue,
                                         OutputValue largeValue);

  public void map(Object arg0, Object arg1, OutputCollector arg2,
                  Reporter arg3) throws IOException {
    throw new IOException("Unsupported operation");
  }
}