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Date: Fri, 13 May 2011 16:34:47 +0000 (UTC)
From: "Jeffrey Naisbitt (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
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Subject: [jira] [Commented] (MAPREDUCE-2489) Jobsplits with random hostnames
 can make the queue unusable
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-2489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13033116#comment-13033116 ] 

Jeffrey Naisbitt commented on MAPREDUCE-2489:
---------------------------------------------

Honestly, I'm not sure what caching was enabled at the time.  How would caching have helped in this case though - where we have basically tons of lookups on garbage hostnames?  (none of these strings are repeated)

> 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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