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https://issues.apache.org/jira/browse/MAPREDUCE-2489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13033129#comment-13033129
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Allen Wittenauer commented on MAPREDUCE-2489:
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Ah, ok, the non-repeating hostnames wasn't clear in the description.
> Jobsplits with random hostnames can make the queue unusable
> -----------------------------------------------------------
>
> Key: MAPREDUCE-2489
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-2489
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: jobtracker
> Reporter: Jeffrey Naisbitt
> Assignee: Jeffrey Naisbitt
>
> We saw an issue where a custom InputSplit was returning invalid hostnames for
> the splits that were then causing the JobTracker to attempt to excessively
> resolve host names. This caused a major slowdown for the JobTracker. We
> should prevent invalid InputSplit hostnames from affecting everyone else.
> I propose we implement some verification for the hostnames to try to ensure
> that we only do DNS lookups on valid hostnames (and fail otherwise). We
> could also fail the job after a certain number of failures in the resolve.
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