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https://issues.apache.org/jira/browse/MAHOUT-326?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844468#action_12844468
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Robin Anil commented on MAHOUT-326:
-----------------------------------
BTW, i hope you tried it with the latest trunk. I see that you have tagged this
issue to version 0.2. If thats the case, I would strongly suggest that you move
to the trunk
> a possible bug with the isConverged() method in KMeansDriver.java
> -----------------------------------------------------------------
>
> Key: MAHOUT-326
> URL: https://issues.apache.org/jira/browse/MAHOUT-326
> Project: Mahout
> Issue Type: Bug
> Components: Clustering
> Affects Versions: 0.2
> Reporter: Chad Chen
> Attachments: mahout_bug.png
>
>
> In one of my today's test runs using the clustering example from the book
> "Mahout in Action", I noticed the following exception thrown by
> KMeansClusterMapper:
> ----------------------------
> java.lang.RuntimeException: Error in configuring object at
> org.apache.hadoop.util.ReflectionUtils.setJobConf(ReflectionUtils.java:93) at
> org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:64) at
> org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:117)
> at org.apache.hadoop.mapred.MapTask.runOldMapper(MapTask.java:354) at
> org.apache.hadoop.mapred.MapTask.run(MapTask.java:307) at
> org.apache.hadoop.mapred.Child.main(Child.java:159) Caused by:
> java.lang.reflect.InvocationTargetException at
> sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597) at
> org.apache.hadoop.util.ReflectionUtils.setJobConf(ReflectionUtils.java:88)
> ... 5 more Caused by: java.lang.RuntimeException: Error in configuring object
> at org.apache.hadoop.util.ReflectionUtils.setJobConf(ReflectionUtils.java:93)
> at org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:64) at
> org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:117)
> at org.apache.hadoop.mapred.MapRunner.configure(MapRunner.java:34) ... 10
> more Caused by: java.lang.reflect.InvocationTargetException at
> sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597) at
> ***
> org.apache.hadoop.util.ReflectionUtils.setJobConf(ReflectionUtils.java:88)
> ... 13 more Caused by: java.lang.NullPointerException: Cluster is empty!!! at
> ***
> org.apache.mahout.clustering.kmeans.KMeansClusterMapper.configure(KMeansClusterMapper.java:63)
> ---------------------------
> which says that the runClustering method didn't see the cluster ouput. The
> same map task did finally succeed after a few failed attempts.
> After looking into KMeansDirver.java, I think may be a bug in the isConverged
> method. Basically, this method doesn't wait for the cluster output file to be
> fully populated. If the part-* file doesn't exist yet or has not been fully
> written, then this method can return true prematurally. I am not sure if this
> is a bug of hadoop itself because it may report successful job before the
> mapred output file is fully written. Meanwhile, a possible way to fix this
> problem is to force the isConverged method to wait for the existence of the
> cluster output file and make sure the file contains the 'converged' values
> for all the clusters.
> Please note, I saw this problem only once in many test runs I had so far. It
> may be a little bit difficult to reproduce. If you need any further
> information, please let me know.
> Thanks.
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