CODEWITHSUNDEEP
javahadoopmapreduce
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Reputation: 1695

MultipleOutputs Zero Reducer

My input folder has 200 files. I want MultipleOutputs to write my parsed inputs from each file(identified using "map.input.file") into an output file with the same name.Since, I don't have any aggregation to perform and so using 0 reducer option (conf.setNumReduceTasks(0)). Ideally, I should get 200 output files.

But, my output has around 5000+ files - each file containing only one line (of streaming output).Clearly, it is not aggregating.My assumption is, Ideally, in zero reducer - mapper output should be aggregated .

Help is appreciated. Thanks! 

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

JobConf conf = new JobConf(MultipleOutputEx.class);
conf.setJobName("Duration Count");

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

conf.setNumReduceTasks(0);
conf.setMapperClass(MultipleOutputExMapper.class);
conf.setReducerClass(MultipleOutputExReducer.class);
conf.setMapOutputKeyClass(NullWritable.class);            
MultipleOutputs.addMultiNamedOutput(conf,"mofiles", TextOutputFormat.class, NullWritable.class, Text.class);    
JobClient.runJob(conf);

}

And my Mapper class is, 

public class MultipleOutputExMapper extends MapReduceBase implements
    Mapper<LongWritable, Text, NullWritable, Text> {

MultipleOutputs mos = null;
Text fileKey = new Text();
String line = "";
private JobConf conf;

@Override
public void configure(JobConf conf) {
    this.conf = conf;
    mos = new MultipleOutputs(conf);
}

public void map(LongWritable key, Text value,
        OutputCollector<NullWritable, Text> output, Reporter reporter)
        throws IOException {
    try {
        String filename = conf.get("map.input.file");
        fileKey.set(filename);
        OutputCollector<NullWritable, Text> collector = mos.getCollector(
                "mofiles", key.toString(), reporter);
        collector.collect(NullWritable.get(), value);

    } catch (ArrayIndexOutOfBoundsException E) {
        E.printStackTrace();
    } catch (Exception E) {
        System.out.println(line);
        E.printStackTrace();
    }
}

@Override
public void close() throws IOException {
    mos.close();
}

Upvotes: 1

Views: 317

Answers (1)

Chris White
Chris White

Reputation: 30089

You're creating an output file for each unique key (as suggested by @climbage in his comment). Try amending to this (untested and uncompiled):

protected OutputCollector<NullWritable, Text> collector = null;
protected String filename = null;

@Override
public void configure(JobConf conf) {
    this.conf = conf;
    mos = new MultipleOutputs(conf);

    // get the filename (just the name, not the path)
    filename = new Path(conf.get("map.input.file")).getName();        
}

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

    try {
        if (collector == null) {
            // create an output collector for the file
            collector = mos.getCollector("mofiles", filename, reporter);
        }

        collector.collect(NullWritable.get(), value);
    } catch (ArrayIndexOutOfBoundsException E) {
        E.printStackTrace();
    } catch (Exception E) {
        System.out.println(line);
        E.printStackTrace();
    }
}

@Override
public void close() throws IOException {
    mos.close();
}

Upvotes: 2

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