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https://issues.apache.org/jira/browse/MAHOUT-326?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chad Chen updated MAHOUT-326:
-----------------------------
Attachment: mahout_bug.png
I am attaching an image to show that the map task failed twice before it
succeeded on the third attempt. Second and third attempts are on the same node
so the node itself should not be the problem. It's more likely that the cluster
output file was ready only on the third attempt.
> 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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