java - Hadoop MapReduce 总排序字数

Question

我想在mapreduce字数统计中进行总排序。

public int run(String[] args) throws Exception {
  Job job = Job.getInstance(getConf(), "wordcount");
  job.setJarByClass(this.getClass());
  FileInputFormat.addInputPath(job, new Path(args[0]));
  FileOutputFormat.setOutputPath(job, new Path(args[1]));
  job.setMapperClass(Map.class);

  //Total Sort
  job.setPartitionerClass(TotalOrderPartitioner.class);
  InputSampler.Sampler<Text, IntWritable> sampler = new InputSampler.RandomSampler<Text, IntWritable>(0.1, 10000, 10);
  InputSampler.writePartitionFile(job, sampler);
  Path inputDir = new Path(args[2] + "/_tmp");
  Path partitionFile = new Path(inputDir, "_partitioning");
  TotalOrderPartitioner.setPartitionFile(job.getConfiguration(),partitionFile);
  InputSampler.writePartitionFile(job, sampler);

  job.setReducerClass(Reduce.class);
  job.setOutputKeyClass(Text.class);
  job.setOutputValueClass(IntWritable.class);  

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

但是我遇到了类似 java.io.IOException: 错误的关键类: org.apache.hadoop.io.Text 不是类 org.apache.hadoop.io.LongWritable

的错误

我不明白 InputSampler.RandomSampler 是如何工作的。

Answer 1

上面的代码中没有 InputFormat为作业设置，因此将采用默认值 TextInputFormat<LongWritable,Text> .

对于InputSampler.RandomSampler<Text, IntWritable>它已被配置为文本，IntWritable，与 TextInputFormat 不匹配.

由于 InputFormat 之间存在类型不匹配和InputSampler抛出错误。