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https://issues.apache.org/jira/browse/HADOOP-10794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14068948#comment-14068948
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Colin Patrick McCabe commented on HADOOP-10794:
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Let's move this to YARN since that's where the issue is (and the solution too, 
hopefully.) :)

Also, YARN != MR.  YARN runs a lot of other stuff.

> A hadoop cluster needs clock synchronization
> --------------------------------------------
>
>                 Key: HADOOP-10794
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10794
>             Project: Hadoop Common
>          Issue Type: Bug
>            Reporter: Zhijie Shen
>
> As a distributed system, a hadoop cluster wants the clock on all the 
> participating hosts synchronized. Otherwise, some problems might happen. For 
> example, in YARN-2251, due to the clock on the host for the task container 
> falls behind that on the host of the AM container, the computed elapsed time 
> (the diff between the timestamps produced on two hosts) becomes negative.
> In YARN-2251, we tried to mask the negative elapsed time. However, we should 
> seek for a decent long term solution, such as providing mechanism to do and 
> check clock synchronization.



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