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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-2026) JobTracker.getJobCounters() should not hold JobTracker lock while calling JobInProgress.getCounters()
Date Tue, 12 Oct 2010 06:55:36 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12920117#action_12920117
] 

dhruba borthakur commented on MAPREDUCE-2026:
---------------------------------------------

>  From our cluster, abount 26% of jobtracker's lock taken by the jsp access.

This is a really good observation. we should measure this for our cluster too. If this is
the case, do you think a reader/writer lock (instead of a synchronized section) might help
performance?

> JobTracker.getJobCounters() should not hold JobTracker lock while calling JobInProgress.getCounters()
> -----------------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-2026
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2026
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>            Reporter: Scott Chen
>            Assignee: Joydeep Sen Sarma
>             Fix For: 0.22.0
>
>         Attachments: MAPREDUCE-2026.txt
>
>
> JobTracker.getJobCounter() will lock JobTracker and call JobInProgress.getCounters().
> JobInProgress.getCounters() can be very expensive because it aggregates all the task
counters.
> We found that from the JobTracker jstacks that this method is one of the bottleneck of
the JobTracker performance.
> JobInProgress.getCounters() should be able to be called out side the JobTracker lock
because it already has JobInProgress lock.
> For example, it is used by jobdetails.jsp without a JobTracker lock.

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