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From Frank Du <frank...@riskmetrics.com>
Subject Encountered NullPointerException with the WordCount example, hadoop common v0.20.1
Date Wed, 03 Feb 2010 20:34:33 GMT
Dear All,

Please help with the NullPointerException in the WordCount example. Sorry it’s the simple
code because I am new to hadoop. :-)

I am running v0.20.1 in Ubuntu 9.10.  The map task works perfectly. But there is NPE with
the reduce task. Is there anything wrong with the configuration or the Reduce.java code?

Below are the error messages from job tracker, and the attached are the source code. Thank
you so much!




Error: java.lang.NullPointerException

        at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:768)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2683)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2605)



Error: java.lang.NullPointerException

        at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:768)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2683)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2605)



Error: java.lang.NullPointerException

        at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:768)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2683)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2605)



Error: java.lang.NullPointerException

        at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:768)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2683)

        at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2605)




- Frank



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