Question

我只是想更好地理解使用多个映射器和reducer。我想尝试使用一个简单的hadoop mapreduce字数计数作业。我想为这个wordcount作业运行两个mapper和两个reducer。就是那个我需要手动配置配置文件，或者只是对WordCount.java文件进行更改。

我在单个节点上运行此作业。我正在运行此作业

$ hadoop jar job.jar输入输出

我已经开始了

$ hadoop namenode -format
$ hadoop namenode

$ hadoop datanode

sbin $ ./yarn-daemon.sh启动resourcemanager sbin $ ./yarn-daemon.sh start resourcemanager

我正在运行hadoop-2.0.0-cdh4.0.0

我的WordCount.java文件是

package org.apache.hadoop.examples;

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.IntWritable;
import org.rg.apache.hadoop.fs.Path;
import oapache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class WordCount {
private static final Log LOG = LogFactory.getLog(WordCount.class);

  public static class TokenizerMapper
       extends Mapper<Object, Text, Text, IntWritable>{

    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    public void map(Object key, Text value, Context context
                    ) throws IOException, InterruptedException {
      StringTokenizer itr = new StringTokenizer(value.toString());
      while (itr.hasMoreTokens()) {
        word.set(itr.nextToken());
        context.write(word, one);
      }
    }
  }

  public static class IntSumReducer
       extends Reducer<Text,IntWritable,Text,IntWritable> {
    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable<IntWritable> values,
                       Context context
                       ) throws IOException, InterruptedException {
      int sum = 0;
      //printKeyAndValues(key, values);

      for (IntWritable val : values) {
        sum += val.get();
      LOG.info("val = " + val.get());
      }
      LOG.info("sum = " + sum + " key = " + key);
      result.set(sum);
      context.write(key, result);
      //System.err.println(String.format("[reduce] word: (%s), count: (%d)", key, result.get()));
    }


  // a little method to print debug output
    private void printKeyAndValues(Text key, Iterable<IntWritable> values)
    {
      StringBuilder sb = new StringBuilder();
      for (IntWritable val : values)
      {
        sb.append(val.get() + ", ");
      }
      System.err.println(String.format("[reduce] key: (%s), value: (%s)", key, sb.toString()));
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    if (otherArgs.length != 2) {
      System.err.println("Usage: wordcount <in> <out>");
      System.exit(2);
    }
    Job job = new Job(conf, "word count");
    job.setJarByClass(WordCount.class);
    job.setMapperClass(TokenizerMapper.class);
    job.setCombinerClass(IntSumReducer.class);
    job.setReducerClass(IntSumReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);
    FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
    FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));

    System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}

你们中的任何人现在可以帮我运行两个映射器和减少器吗？

Answer 1

Gladnick：如果您打算使用默认的 TextInputFormat ，那么输入文件数量上将至少有多个映射器（或者更多，具体取决于文件大小）。所以只需将2个文件放入输入目录，这样就可以运行2个映射器。（建议此解决方案，因为您计划将其作为测试用例运行）。

既然您已经要求2个减速器，那么您需要做的就是提交作业的主要原因是 job.setNumReduceTasks（2）。

之后，只需准备一个应用程序的jar并在 hadoop伪群集中运行它。

如果您需要指定哪个单词去哪个reducer，您可以在Partitioner类中指定。

            Configuration configuration = new Configuration();
        // create a configuration object that provides access to various
        // configuration parameters
        Job job = new Job(configuration, "Wordcount-Vowels & Consonants");
        // create the job object and set job name as Wordcount-Vowels &
        // Consonants
        job.setJarByClass(WordCount.class);
        // set the main class
        job.setNumReduceTasks(2);
        // set the number of reduce tasks required
        job.setMapperClass(WordCountMapper.class);
        // set the map class for the job
        job.setCombinerClass(WordCountCombiner.class);
        // set the combiner class for the job
        job.setPartitionerClass(VowelConsonantPartitioner.class);
        // set the partitioner class for the job
        job.setReducerClass(WordCountReducer.class);
        // set the reduce class for the job
        job.setOutputKeyClass(Text.class);
        // set the output type of key (the word) expected from the job, Text
        // analogous to String
        job.setOutputValueClass(IntWritable.class);
        // set the output type of value (the count) expected from the job,
        // IntWritable analogous to int
        FileInputFormat.addInputPath(job, new Path(args[0]));
        // set the input directory for fetching the input files
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

这应该是主程序的结构。如果需要，您可以包括组合器和分区器。

Answer 2

对于映射器设置

mapred.max.split.size

是文件大小的一半。

对于reducers，将它们明确地设置为2

 mapred.reduce.tasks=2

为简单的hadoop mapreduce作业运行两个映射器和两个reducer

2 个答案: