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https://issues.apache.org/jira/browse/HADOOP-10048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15342775#comment-15342775
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Junping Du commented on HADOOP-10048:
-------------------------------------

I would prefer not to backport to 2.6 and 2.7 for the same reason as [~jlowe] 
mentioned. This is a performance gain but not a bug fix which should be kept 
out of maintenance release as our previous practices.

> LocalDirAllocator should avoid holding locks while accessing the filesystem
> ---------------------------------------------------------------------------
>
>                 Key: HADOOP-10048
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10048
>             Project: Hadoop Common
>          Issue Type: Improvement
>    Affects Versions: 2.3.0
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>             Fix For: 2.8.0
>
>         Attachments: HADOOP-10048.003.patch, HADOOP-10048.004.patch, 
> HADOOP-10048.005.patch, HADOOP-10048.006.patch, HADOOP-10048.patch, 
> HADOOP-10048.trunk.patch
>
>
> As noted in MAPREDUCE-5584 and HADOOP-7016, LocalDirAllocator can be a 
> bottleneck for multithreaded setups like the ShuffleHandler.  We should 
> consider moving to a lockless design or minimizing the critical sections to a 
> very small amount of time that does not involve I/O operations.



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