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https://issues.apache.org/jira/browse/MAPREDUCE-969?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Todd Lipcon updated MAPREDUCE-969:
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Attachment: reduce_task_logs
bad_job_jt_logs
bad_job_events
Attaching sanitized logs from this incident.
The event that seems to be a red flag is the lost task tracker xx05.
The null pointer exception is caused by u.getHost() being null - this URI is
the taskTrackerHttpAddress in a TaskTrackerStatus. The job event output doesn't
show any with a malformed URL, so I suspect some kind of race.
Aside from this issue, I find it odd that GetMapEventsThread ignores
exceptions. In cases like this it will cause the ReduceTask to spin forever
while still reporting progress until the user intervenes.
> 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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