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From "Jothi Padmanabhan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-969) NullPointerException during reduce freezes job
Date Fri, 11 Sep 2009 03:23:59 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-969?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12753964#action_12753964

Jothi Padmanabhan commented on MAPREDUCE-969:

OK, from our earlier investigations, this was primarily caused by HADOOP-4744. We were never
really able to reproduce this consistently and evidently the work arounds in 4744 has not

GetMapEventsThread ignoring exceptions -- you are right. We probably should catch and bail
out. We did this change for MAPREDUCE-318. We probably should port it to 20 as well.

> 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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