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https://issues.apache.org/jira/browse/MAPREDUCE-2026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12970990#action_12970990
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Joydeep Sen Sarma commented on MAPREDUCE-2026:
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For this particular patch:
[exec] Please justify why no new tests are needed for this patch.
- the patch improves performance of existing functionality - the tests for
those existing functionality (getCounters) will test whether this patch is
working correctly. there is no new functionality or change in behavior of
existing functionality
- it's impossible to trigger specific race conditions (to test changes in
locking) without having support for fault/sleep injection in hadoop code base.
[exec] Also please list what manual steps were performed to verify this patch.
i have already mentioned this - this patch has been in production in all
Facebook Hadoop clusters for a couple of months now.
thanks for taking a look.
> 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: 2026.1.patch, 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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