Hadoop MapReduce总排序字数

Question

I want to do a total sort in mapreduce Word Count.

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;
}

But i got error like java.io.IOException: wrong key class: org.apache.hadoop.io.Text is not class org.apache.hadoop.io.LongWritable

I don't understand how InputSampler.RandomSampler work.

Answer 1

In the above code there is no InputFormat set for the job, so default will be taken which is TextInputFormat<LongWritable,Text> .

For InputSampler.RandomSampler<Text, IntWritable> it has been configured as Text, IntWritable which doesn't match with TextInputFormat .

Since there is type mismatch between InputFormat and InputSampler the error is thrown.