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Posted to mapreduce-issues@hadoop.apache.org by "Jothi Padmanabhan (JIRA)" <ji...@apache.org> on 2009/09/11 05:23:59 UTC
[jira] Commented: (MAPREDUCE-969) NullPointerException during
reduce freezes job
[ 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 helped...
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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