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POinfinitely loop for org.apache.hadoop.mapred.TaskTracker
 

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    <p>I am running one simple hadoop application which collect information from a 64MB file, the map finished quickly, roughly in about 2 -5 minutes, then reduce also runs fast up to 16%, then it just stopped. </p> <p>This is the program output</p> <pre> 11/12/20 17:53:46 INFO input.FileInputFormat: Total input paths to process : 1 11/12/20 17:53:46 INFO mapred.JobClient: Running job: job_201112201749_0001 11/12/20 17:53:47 INFO mapred.JobClient: map 0% reduce 0% 11/12/20 17:54:06 INFO mapred.JobClient: map 4% reduce 0% 11/12/20 17:54:09 INFO mapred.JobClient: map 15% reduce 0% 11/12/20 17:54:12 INFO mapred.JobClient: map 28% reduce 0% 11/12/20 17:54:15 INFO mapred.JobClient: map 40% reduce 0% 11/12/20 17:54:18 INFO mapred.JobClient: map 53% reduce 0% 11/12/20 17:54:21 INFO mapred.JobClient: map 64% reduce 0% 11/12/20 17:54:24 INFO mapred.JobClient: map 77% reduce 0% 11/12/20 17:54:27 INFO mapred.JobClient: map 89% reduce 0% 11/12/20 17:54:30 INFO mapred.JobClient: map 98% reduce 0% 11/12/20 17:54:33 INFO mapred.JobClient: map 100% reduce 0% 11/12/20 17:54:54 INFO mapred.JobClient: map 100% reduce 8% 11/12/20 17:54:57 INFO mapred.JobClient: map 100% reduce 16% </pre> <p>In the data node log, I see tons of same message again and again, the following is there is starts, </p> <pre> 2011-12-20 17:54:51,353 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.083333336% reduce > copy (1 of 4 at 9.01 MB/s) > 2011-12-20 17:54:51,507 INFO org.apache.hadoop.mapred.TaskTracker.clienttrace: src: 127.0.1.1:50060, dest: 127.0.0.1:44367, bytes: 75623263, op: MAPRED_SHUFFLE, cliID: attempt_201112201749_0001_m_000000_0, duration: 2161793492 2011-12-20 17:54:54,389 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:54:57,433 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:55:40,359 INFO org.mortbay.log: org.mortbay.io.nio.SelectorManager$SelectSet@53d3cf JVM BUG(s) - injecting delay3 times 2011-12-20 17:55:40,359 INFO org.mortbay.log: org.mortbay.io.nio.SelectorManager$SelectSet@53d3cf JVM BUG(s) - recreating selector 3 times, canceled keys 72 times 2011-12-20 17:57:51,518 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:57:57,536 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:58:03,554 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > </pre> <p>...</p> <p>up to</p> <pre> 2011-12-20 17:54:51,353 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.083333336% reduce > copy (1 of 4 at 9.01 MB/s) > 2011-12-20 17:54:51,507 INFO org.apache.hadoop.mapred.TaskTracker.clienttrace: src: 127.0.1.1:50060, dest: 127.0.0.1:44367, bytes: 75623263, op: MAPRED_SHUFFLE, cliID: attempt_201112201749_0001_m_000000_0, duration: 2161793492 2011-12-20 17:54:54,389 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:54:57,433 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:55:40,359 INFO org.mortbay.log: org.mortbay.io.nio.SelectorManager$SelectSet@53d3cf JVM BUG(s) - injecting delay3 times 2011-12-20 17:55:40,359 INFO org.mortbay.log: org.mortbay.io.nio.SelectorManager$SelectSet@53d3cf JVM BUG(s) - recreating selector 3 times, canceled keys 72 times 2011-12-20 17:57:51,518 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:57:57,536 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > 2011-12-20 17:58:03,554 INFO org.apache.hadoop.mapred.TaskTracker: attempt_201112201749_0001_r_000000_0 0.16666667% reduce > copy (2 of 4 at 14.42 MB/s) > </pre> <p>Here is the code</p> <pre>package com.bluedolphin; import java.io.IOException; import java.util.Iterator; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.Path; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.Mapper; import org.apache.hadoop.mapreduce.Reducer; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat; import org.apache.hadoop.util.GenericOptionsParser; public class MyJob { private final static LongWritable one = new LongWritable(1); private final static Text word = new Text(); public static class MyMapClass extends Mapper&lt;LongWritable, Text, Text, LongWritable&gt; { public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException { String[] citation = value.toString().split(","); word.set(citation[0]); context.write(word, one); } } public static class MyReducer extends Reducer&lt;Text, LongWritable, Text, LongWritable&gt; { private LongWritable result = new LongWritable(); public void reduce( Text key, Iterator&lt;LongWritable&gt; values, Context context) throws IOException, InterruptedException { int sum = 0; while (values.hasNext()) { sum += values.next().get(); } result.set(sum); context.write(key, result); } } public static void main(String[] args) throws Exception { Configuration conf = new Configuration(); String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs(); if (otherArgs.length != 2) { System.err.println("Usage: myjob &lt;in&gt; &lt;out&gt;"); System.exit(2); } Job job = new Job(conf, "patent citation"); job.setJarByClass(MyJob.class); job.setMapperClass(MyMapClass.class); // job.setCombinerClass(MyReducer.class); // job.setReducerClass(MyReducer.class); job.setNumReduceTasks(0); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(LongWritable.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(LongWritable.class); FileInputFormat.addInputPath(job, new Path(otherArgs[0])); FileOutputFormat.setOutputPath(job, new Path(otherArgs[1])); System.exit(job.waitForCompletion(true) ? 0 : 1); } } </pre> <p>I don't know how to further troubleshooting. </p> <p>Thanks in advace.</p>
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    1. USBlueDolphin
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    1. COLooks like the reducers are breaking in the shuffle and sort phase. It would be better if you can tell what key value pair your mappers are emitting.
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      1. USNishant Nagwani
    2. COIs it eating up CPU?
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      1. USJoseph Shraibman
    3. COI uploaded code. The reducer is really simple, I don't see it could have infinite loop. And the CPU usage seems fine, I could do other work like browsing or even install and test mahout without any feeling of slow.
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      1. USBlueDolphin
 

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