java - MapReduce不产生输出

Question

我想在文本文件上执行一个简单的MapReduce，但它没有输出。这是我的代码:

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.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;

public class WordCount {

  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;
      for (IntWritable val : values) {
        sum += val.get();
      }
      result.set(sum) ;
      context.write(key, result);
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(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(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

我在执行jar文件的过程中收到以下错误消息:

17/05/07 23:10:53 WARN mapred.LocalJobRunner: job_local973452829_0001
java.lang.Exception:     org.apache.hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in localfetcher#1
at org.apache.hadoop.mapred.LocalJobRunner$Job.runTasks(LocalJobRunner.java:462)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:529)
Caused by: org.apache.hadoop.mapreduce.task.reduce.Shuffle$ShuffleError: error in shuffle in localfetcher#1
at org.apache.hadoop.mapreduce.task.reduce.Shuffle.run(Shuffle.java:134)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:376)
at org.apache.hadoop.mapred.LocalJobRunner$Job$ReduceTaskRunnable.run(LocalJobRunner.java:319)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.io.FileNotFoundException: /app/hadoop/tmp%20/mapred/local/localRunner/hduser/jobcache/job_local973452829_0001/attempt_local973452829_0001_m_000000_0/output/file.out.index
at org.apache.hadoop.fs.RawLocalFileSystem.open(RawLocalFileSystem.java:193)
at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:764)
at org.apache.hadoop.io.SecureIOUtils.openFSDataInputStream(SecureIOUtils.java:156)
at org.apache.hadoop.mapred.SpillRecord.<init>(SpillRecord.java:70)
at org.apache.hadoop.mapred.SpillRecord.<init>(SpillRecord.java:62)
at org.apache.hadoop.mapred.SpillRecord.<init>(SpillRecord.java:57)
at org.apache.hadoop.mapreduce.task.reduce.LocalFetcher.copyMapOutput(LocalFetcher.java:123)
at org.apache.hadoop.mapreduce.task.reduce.LocalFetcher.doCopy(LocalFetcher.java:101)
at org.apache.hadoop.mapreduce.task.reduce.LocalFetcher.run(LocalFetcher

我的代码有什么问题？我在Hadoop 14.04和Hadoop 2.4下

Answer 1

这是您的错误的一部分:
Caused by: java.io.FileNotFoundException: /app/hadoop/tmp%20/mapred/local/localRunner/hduser/jobcache/job_local973452829_0001/attempt_local973452829_0001_m_000000_0/output/file.out.index
我猜这是hadoop.tmp.dir中的配置属性core-site.xml的问题，因为Hadoop无法将临时输出文件(来自Mapper)存储到磁盘上。

您可以删除该属性，以便hadoop创建其自己的临时目录来存储中间输出，或将其设置为具有适当权限的某个目录。