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https://issues.apache.org/jira/browse/HADOOP-10048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15299261#comment-15299261
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Junping Du commented on HADOOP-10048:
-------------------------------------
Thanks [~jlowe] for updating the patch. I am OK with lockless approach to solve
the problem. However, in the existing patch (004), it seems cannot guarantee
the consistency for Async call of {{getLocalPathForWrite(.., conf, ...)}} with
conf in multi-thread case if conf get changed.
Consider the case that thread A (conf1) and thread B (conf2) call this method
at the same time: thread A hit confChanged() with conf1 first, then thread B
hit confChanged() with conf2, afterwards thread A going forward to get path for
write that is based on conf2 now - that means thread A could get a path that is
not existed in conf1.
I think we should keep the consistency between API's return result and
parameter, like: we can let confChanged() return a thread local Context object
and do the following thing with this local context. What do you think?
> 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
> Attachments: HADOOP-10048.003.patch, HADOOP-10048.004.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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