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From "Devaraj Das (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3236) Reduce task failed at shuffling time, throwing null pointer exception
Date Fri, 11 Apr 2008 19:38:04 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3236?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12588089#action_12588089

Devaraj Das commented on HADOOP-3236:

Actually, whenever there is an error in the merge, the InMemoryFileSystem is left in a state
where other threads using the InMemoryFileSystem would encounter NPEs. This needs to be fixed.
But it's not a correctness issue since if there is a merge exception the task will die for

So yes the NPEs are due to the other merge exceptions as you pointed out. But I am not sure
why so many reducers are seeing corrupted map outputs.

> Reduce task failed at shuffling time, throwing null pointer exception
> ---------------------------------------------------------------------
>                 Key: HADOOP-3236
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3236
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Runping Qi
> This happened for 0.17.0 branch.
> Here is the stack trace:
> 2008-04-11 13:45:54,171 ERROR org.apache.hadoop.mapred.ReduceTask: Map output copy failure:
> 	at org.apache.hadoop.fs.InMemoryFileSystem$RawInMemoryFileSystem.getFileStatus(InMemoryFileSystem.java:302)
> 	at org.apache.hadoop.fs.FilterFileSystem.getFileStatus(FilterFileSystem.java:242)
> 	at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.copyOutput(ReduceTask.java:853)
> 	at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.run(ReduceTask.java:777)

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