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https://issues.apache.org/jira/browse/MAPREDUCE-4464?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Clint Heath updated MAPREDUCE-4464:
-----------------------------------
Hadoop Flags: Reviewed
Status: Patch Available (was: Open)
> Reduce tasks failing with NullPointerException in ConcurrentHashMap.get()
> -------------------------------------------------------------------------
>
> Key: MAPREDUCE-4464
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4464
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: task
> Affects Versions: 1.0.0
> Reporter: Clint Heath
> Assignee: Clint Heath
> Priority: Minor
> Attachments: MAPREDUCE-4464_new.patch, MAPREDUCE-4464.patch
>
> Original Estimate: 1h
> Remaining Estimate: 1h
>
> If DNS does not resolve hostnames properly, reduce tasks can fail with a very
> misleading exception.
> as per my peer Ahmed's diagnosis:
> In ReduceTask, it seems that event.getTaskTrackerHttp() returns a malformed
> URI, and so host from:
> {code}
> String host = u.getHost();
> {code}
> is evaluated to null and the NullPointerException is thrown afterwards in the
> ConcurrentHashMap.
> I have written a patch to check for a null hostname condition when getHost is
> called in the getMapCompletionEvents method and print an intelligible warning
> message rather than suppressing it until later when it becomes confusing and
> misleading.
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