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Posted to mapreduce-issues@hadoop.apache.org by "Harsh J (JIRA)" <ji...@apache.org> on 2012/09/27 18:32:07 UTC
[jira] [Updated] (MAPREDUCE-4464) Reduce tasks failing with
NullPointerException in ConcurrentHashMap.get()
[ https://issues.apache.org/jira/browse/MAPREDUCE-4464?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Harsh J updated MAPREDUCE-4464:
-------------------------------
Attachment: MAPREDUCE-4464.patch
I improved the message in Clint's patch a slight bit to indicate what to look at.
And I could also successfully reproduce the issue on a forced bad hostname machine (devel_vm.vm):
{code}
12/09/27 21:52:16 INFO mapred.JobClient: Task Id : attempt_201209272149_0001_r_000000_2, Status : FAILED
Error: java.io.IOException: Invalid hostname found in tracker location: 'http://devel_vm.vm:50060'
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.getMapCompletionEvents(ReduceTask.java:2920)
at org.apache.hadoop.mapred.ReduceTask$ReduceCopier$GetMapEventsThread.run(ReduceTask.java:2845)
{code}
> 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, 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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