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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-969) NullPointerException during reduce freezes job
Date Thu, 10 Sep 2009 23:45:57 GMT
NullPointerException during reduce freezes job
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                 Key: MAPREDUCE-969
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-969
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: jobtracker, task, tasktracker
    Affects Versions: 0.20.2
            Reporter: Todd Lipcon
            Assignee: Todd Lipcon


We experienced several jobs stuck in Reduce on a cluster. All of the stuck reduce tasks had
a similar were stuck at "Need another 2 map output(s) where 0 is already in progress" despite
all of the mappers having completed, and 0 scheduled. The stuck reducers had experienced the
following exception early in the shuffle:

java.lang.NullPointerException
	at java.util.concurrent.ConcurrentHashMap.get(ConcurrentHashMap.java:768)
	at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2747)
	at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2670)

Will attach more information and logs momentarily.

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