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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-969) NullPointerException during reduce freezes job
Date Fri, 11 Sep 2009 03:34:57 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-969?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12753968#action_12753968

Todd Lipcon commented on MAPREDUCE-969:

Yea, I looked at HADOOP-4744 as well as a couple other JIRAs but wasn't able to figure it
out. If it keeps popping up, we will instrument the code with some debug logging and see if
we can track it down.

> NullPointerException during reduce freezes job
> ----------------------------------------------
>                 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
>         Attachments: bad_job_events, bad_job_jt_logs, reduce_task_logs
> 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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