Hadoop mapper and reducer value type mismatch error

Question

I am new with hadoop and have encountered this problem. I am trying to change the default Text,Integer values for the reducer to Text, Text. I want to map Text,IntWritable then in the reducer I want to have 2 counters depending what the value is and then write those 2 counters in a Text for the collector.

public class WordCountMapper extends MapReduceBase
    implements Mapper<LongWritable, Text, Text, IntWritable> {

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

  public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable>
        output, Reporter reporter) throws IOException {

    String line = value.toString();
    String[] words = line.split(",");
    String[] date = words[2].split(" ");
      word.set(date[0]+" "+date[1]+" "+date[2]);
      if(words[0].contains("0"))
          one.set(0);
      else
          one.set(4);
      output.collect(word, one);

  }
}

-----------------------------------------------------------------------------------

public class WordCountReducer extends MapReduceBase
    implements Reducer<Text, IntWritable, Text, Text> {

  public void reduce(Text key,Iterator<IntWritable> values,
                  OutputCollector<Text, Text> output,
                  Reporter reporter) throws IOException {

    int sad = 0;
    int happy = 0;
    while (values.hasNext()) {
      IntWritable value = (IntWritable) values.next();
      if(value.get() == 0)
          sad++; // process value
      else
          happy++;
    }

    output.collect(key, new Text("sad:"+sad+", happy:"+happy));
  }
}
---------------------------------------------------------------------------------

public class WordCount {

  public static void main(String[] args) {
    JobClient client = new JobClient();
    JobConf conf = new JobConf(WordCount.class);

    // specify output types
    conf.setOutputKeyClass(Text.class);
    conf.setOutputValueClass(IntWritable.class);

    // specify input and output dirs
    FileInputFormat.addInputPath(conf, new Path("input"));
    FileOutputFormat.setOutputPath(conf, new Path("output"));

    // specify a mapper
    conf.setMapperClass(WordCountMapper.class);

    // specify a reducer
    conf.setReducerClass(WordCountReducer.class);
    conf.setCombinerClass(WordCountReducer.class);

    client.setConf(conf);
    try {
      JobClient.runJob(conf);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

I get this error:

14/12/10 18:11:01 INFO mapred.JobClient: Task Id : attempt_201412100143_0008_m_000000_0, Status : FAILED java.io.IOException: Spill failed at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:425) at WordCountMapper.map(WordCountMapper.java:31) at WordCountMapper.map(WordCountMapper.java:1) at org.apache.hadoop.mapred.MapRunner.run(MapRunner.java:47) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:227) at org.apache.hadoop.mapred.TaskTracker$Child.main(TaskTracker.java:2209) Caused by: java.io.IOException: wrong value class: class org.apache.hadoop.io.Text is not class org.apache.hadoop.io.IntWritable at org.apache.hadoop.mapred.IFile$Writer.append(IFile.java:143) at org.apache.hadoop.mapred.Task$CombineOutputCollector.collect(Task.java:626) at WordCountReducer.reduce(WordCountReducer.java:29) at WordCountReducer.reduce(WordCountReducer.java:1) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.combineAndSpill(MapTask.java:904) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.sortAndSpill(MapTask.java:785) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.access$1600(MapTask.java:286) at org.apache.hadoop.mapred.MapTask$MapOutputBuffer$SpillThread.run(MapTask.java:712)

The error repeats itself several times after this. Could someone explain why this error occurs? I searched similar errors as this one but all I found were mismatched key-value types for the mapper and the reducer, but as I can see I have matching key-value types for the mapper and reducer. Thank you in advance.

USB USB · Accepted Answer · 2014-12-11T10:29:01

Try commenting

conf.setCombinerClass(WordCountReducer.class);

and run.

It is because the Data buffer may get full.

Spill error

Also include

job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(IntWritable.class);

job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);

as Map and Reducer emits different Key-value datatypes.

If both are emitting same datatypes then

job.setOutputKeyClass();
job.setOutputValueClass();

is enough.

Hadoop mapper and reducer value type mismatch error

2 Answers