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https://issues.apache.org/jira/browse/MAPREDUCE-5940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14051345#comment-14051345
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Junping Du commented on MAPREDUCE-5940:
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bq. Silently making the elapsed time as 0 when it is negative may lead to 
hiding the bugs related to elapsed time. Adding a warning/info message before 
making it as 0 would help to diagnose/find out the issues if any.
Agree. I have similar comments above.

> Avoid negative elapsed time in JHS/MRAM web UI and services
> -----------------------------------------------------------
>
>                 Key: MAPREDUCE-5940
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5940
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: jobhistoryserver, mr-am, webapps
>            Reporter: Zhijie Shen
>            Assignee: Zhijie Shen
>         Attachments: MAPREDUCE-5940.1.patch
>
>
> Recently we observed a rare bug that an elapsed time of a reducer is going to 
> be negative on JHS web UI and via REST APIs. While the real reason for this 
> bug seems to be clock asynchronization on different hosts, the web frontend 
> should have masked the negative values. However, in the current code, 
> *org.apache.hadoop.mapreduce.v2.app.webapp.dao.** only check whether the 
> elapsed time is -1 or not.



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