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https://issues.apache.org/jira/browse/MAPREDUCE-5940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14051610#comment-14051610
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Zhijie Shen commented on MAPREDUCE-5940:
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Thanks for review, Junping and Devaraj.
bq. If System.currentTimeMillis() < started, then we can return -1 or 0 instead
IMHO, Times#elapsed is to computed the delta between two timestamps: started
and finished. Given System.currentTimeMillis() < started <= finished, it still
should be a valid case. To make sure the elapsed time should always be
non-negative, we need to check started <= finished, and return -1 if not.
bq. (and log a warn that clock not getting synchronized)
bq. Adding a warning/info message before making it as 0 would help to
diagnose/find out the issues if any.
bq. Also adding a test in TestTimes.java could be a good idea.
Sounds a good idea. Will address it in the new patch.
In addition, add a code comment to explicitly declare the behavior of
Times#elapsed
> 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, MAPREDUCE-5940.2.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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