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POHadoop: Reducer writing Mapper output into Output File
 

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  1. POHadoop: Reducer writing Mapper output into Output File
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    <p>I met a very very strange problem. The reducers do work but if I check the output files, I only found the output from the mappers. When I was trying to debug, I found the same problem with the word count sample after I changed the mappers' output value type from Longwritable to Text </p> <pre><code> package org.myorg; import java.io.IOException; import java.util.*; import org.apache.hadoop.fs.Path; import org.apache.hadoop.conf.*; import org.apache.hadoop.io.*; import org.apache.hadoop.mapreduce.*; import org.apache.hadoop.mapreduce.lib.input.*; import org.apache.hadoop.mapreduce.lib.output.*; import org.apache.hadoop.util.*; public class WordCount extends Configured implements Tool { public static class Map extends Mapper&lt;LongWritable, Text, Text, Text&gt; { private final static IntWritable one = new IntWritable(1); private Text word = new Text(); public void map(LongWritable key, Text wtf, Context context) throws IOException, InterruptedException { String line = wtf.toString(); StringTokenizer tokenizer = new StringTokenizer(line); while (tokenizer.hasMoreTokens()) { word.set(tokenizer.nextToken()); context.write(word, new Text("frommapper")); } } } public static class Reduce extends Reducer&lt;Text, Text, Text, Text&gt; { public void reduce(Text key, Text wtfs, Context context) throws IOException, InterruptedException { /* int sum = 0; for (IntWritable val : wtfs) { sum += val.get(); } context.write(key, new IntWritable(sum));*/ context.write(key,new Text("can't output")); } } public int run(String [] args) throws Exception { Job job = new Job(getConf()); job.setJarByClass(WordCount.class); job.setJobName("wordcount"); job.setOutputKeyClass(Text.class); job.setMapOutputValueClass(Text.class); job.setOutputValueClass(Text.class); job.setMapperClass(Map.class); //job.setCombinerClass(Reduce.class); job.setReducerClass(Reduce.class); job.setInputFormatClass(TextInputFormat.class); job.setOutputFormatClass(TextOutputFormat.class); FileInputFormat.setInputPaths(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); boolean success = job.waitForCompletion(true); return success ? 0 : 1; } public static void main(String[] args) throws Exception { int ret = ToolRunner.run(new WordCount(), args); System.exit(ret); } } </code></pre> <p>here are the results </p> <pre><code>JobClient: Combine output records=0 12/06/13 17:37:46 INFO mapred.JobClient: Map input records=7 12/06/13 17:37:46 INFO mapred.JobClient: Reduce shuffle bytes=116 12/06/13 17:37:46 INFO mapred.JobClient: Reduce output records=7 12/06/13 17:37:46 INFO mapred.JobClient: Spilled Records=14 12/06/13 17:37:46 INFO mapred.JobClient: Map output bytes=96 12/06/13 17:37:46 INFO mapred.JobClient: Combine input records=0 12/06/13 17:37:46 INFO mapred.JobClient: Map output records=7 12/06/13 17:37:46 INFO mapred.JobClient: Reduce input records=7 </code></pre> <p>then I found the strange results in the outfile. This problem happened after I changed the output value type of map and input key type of reducer to Text no matter I changed the type of reduce output value or not. I was also forced to change job.setOutputValue(Text.class)</p> <pre><code>a frommapper a frommapper a frommapper gg frommapper h frommapper sss frommapper sss frommapper </code></pre> <p>Help!</p>
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    1. USChaos
    1. UStony marbo
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    1. COShould the signature of the reduce function be something like: reduce(KEYIN key, Iterable<VALUEIN> values, Reducer.Context context)? You do not have the Iterable<Text> part in there.
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      1. POHadoop: Reducer writing Mapper output into Output File
      1. USJeff Wu
 

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