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POTwo equal combine keys do not get to the same reducer
 

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  1. POTwo equal combine keys do not get to the same reducer
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    <p>I'm making a Hadoop application in Java with the MapReduce framework.</p> <p>I use only Text keys and values for both input and output. I use a combiner to do an extra step of computations before reducing to the final output.</p> <p>But I have the problem that the keys do not go to the same reducer. I create and add the key/value pair like this in the combiner: </p> <pre><code>public static class Step4Combiner extends Reducer&lt;Text,Text,Text,Text&gt; { private static Text key0 = new Text(); private static Text key1 = new Text(); public void reduce(Text key, Iterable&lt;Text&gt; values, Context context) throws IOException, InterruptedException { key0.set("KeyOne"); key1.set("KeyTwo"); context.write(key0, new Text("some value")); context.write(key1, new Text("some other value")); } } public static class Step4Reducer extends Reducer&lt;Text,Text,Text,Text&gt; { public void reduce(Text key, Iterable&lt;Text&gt; values, Context context) throws IOException, InterruptedException { System.out.print("Key:" + key.toString() + " Value: "); String theOutput = ""; for (Text val : values) { System.out.print("," + val); } System.out.print("\n"); context.write(key, new Text(theOutput)); } } </code></pre> <p>In the main i creates the job like this:</p> <pre><code>Configuration conf = new Configuration(); String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs(); Job job4 = new Job(conf, "Step 4"); job4.setJarByClass(Step4.class); job4.setMapperClass(Step4.Step4Mapper.class); job4.setCombinerClass(Step4.Step4Combiner.class); job4.setReducerClass(Step4.Step4Reducer.class); job4.setInputFormatClass(TextInputFormat.class); job4.setOutputKeyClass(Text.class); job4.setOutputValueClass(Text.class); FileInputFormat.addInputPath(job4, new Path(outputPath)); FileOutputFormat.setOutputPath(job4, new Path(finalOutputPath)); System.exit(job4.waitForCompletion(true) ? 0 : 1); </code></pre> <p>The output in stdout printed from the reducer is this:</p> <pre><code>Key:KeyOne Value: ,some value Key:KeyTwo Value: ,some other value Key:KeyOne Value: ,some value Key:KeyTwo Value: ,some other value Key:KeyOne Value: ,some value Key:KeyTwo Value: ,some other value </code></pre> <p>Which makes no sense since the keys are the same, and therefore it should be 2 reducers with 3 of the same values in it's Iterable</p> <p>Hope you can help me get to the bottom of this :)</p>
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    1. USgreedybuddha
    1. USBjarkes
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      1. USThe_Agape
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    1. COIt would help if you get us the complete code ;) As seeing the code snippets here, it looks fine. Problem is somewhere else I believe.
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      1. USAmar
    2. COAre you using the same class as your combiner as well as reducer ?
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      1. USAmar
    3. COI added the whole combiner and reducer, that are all dummy just to show the problem at its minimum.
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      1. USBjarkes
 

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