Question

Anyone have any idea why I would be getting this error? I have looked at alot of other similar posts but most of them did not apply to me, I also tried the few solutions that were posted that did apply to me but they did not work, I’m sure I’m just missing something stupid, thanks for the help

chris@chrisUHadoop:/usr/local/hadoop-1.0.3/build$ hadoop MaxTemperature 1901 output4
12/07/03 17:23:08 WARN mapred.JobClient: Use GenericOptionsParser for parsing the     arguments. Applications should implement Tool for the same.
12/07/03 17:23:08 INFO input.FileInputFormat: Total input paths to process : 1
12/07/03 17:23:08 INFO util.NativeCodeLoader: Loaded the native-hadoop library
12/07/03 17:23:08 WARN snappy.LoadSnappy: Snappy native library not loaded
12/07/03 17:23:09 INFO mapred.JobClient: Running job: job_201207031642_0005
12/07/03 17:23:10 INFO mapred.JobClient:  map 0% reduce 0%
12/07/03 17:23:28 INFO mapred.JobClient: Task Id : attempt_201207031642_0005_m_000000_0, Status : FAILED
java.io.IOException: Type mismatch in key from map: expected org.apache.hadoop.io.Text, recieved org.apache.hadoop.io.LongWritable
at org.apache.hadoop.mapred.MapTask$MapOutputBuffer.collect(MapTask.java:1014)
at org.apache.hadoop.mapred.MapTask$NewOutputCollector.write(MapTask.java:691)
at org.apache.hadoop.mapreduce.TaskInputOutputContext.write(TaskInputOutputContext.java:80)
at org.apache.hadoop.mapreduce.Mapper.map(Mapper.java:124)
at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:764)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.Child$4.run(Child.java:255)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121)
at org.apache.hadoop.mapred.Child.main(Child.java:249)

Program:

import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class MaxTemperatureMapper extends Mapper<LongWritable, Text, Text, IntWritable>{

private static final int MISSING = 9999;

@Override
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException
{
    String line = value.toString();
    String year = line.substring(15,19);
    int airTemperature;
    if (line.charAt(87) == '+')
    {
        airTemperature = Integer.parseInt(line.substring(88,92));
    }
    else
    {
        airTemperature = Integer.parseInt(line.substring(87,92));
    }
    String quality = line.substring(92,93);
    if (airTemperature != MISSING && quality.matches("[01459]"))
    {
        context.write(new Text(year), new IntWritable(airTemperature));
    }
}

}

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class MaxTemperatureReducer extends Reducer<Text, IntWritable, Text, IntWritable>
{
@Override
public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException
{
    int maxValue = Integer.MIN_VALUE;
    for (IntWritable value : values)
    {
        maxValue = Math.max(maxValue, value.get());
    }
    context.write(key, new IntWritable(maxValue));
}
}

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.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MaxTemperature 
{

public static void main(String[] args) throws Exception 
{
    if (args.length != 2)
    {
        System.out.println("Usage: MaxTemperature <input path> <output path>");
        System.exit(-1);
    }

    Job job = new Job();
    job.setJarByClass(MaxTemperature.class);
    job.setJobName("Max temperature");

    FileInputFormat.addInputPath(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

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

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

}
}

Answer 1

You appear to be missing a number of configuration properties:

• Mapper and Reducer classes? – if not defined, you’ll be defaulted to the ‘Identity’ Mapper / Reducer

Your specific error message is because the identity mapper just outputs the same key / value types it was passed in, in this case probably a key of type LongWritable and value of type Text (as you haven’t defined an Input format, the default is probably TextInputFormat). In your configuration you have defined the output key type as Text, but the mapper is outputting LongWritable, hence the error message.