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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