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From "Junping Du (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10048) LocalDirAllocator should avoid holding locks while accessing the filesystem
Date Wed, 25 May 2016 18:29:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15300600#comment-15300600
] 

Junping Du commented on HADOOP-10048:
-------------------------------------

Thanks [~jlowe] for updating the patch!
005 patch looks good in overall. Just two minor issues:
{noformat}
+          ctx.dirNumLastAccessed = dirNum;
{noformat}
Given the ctx could be local context, I think we want to update it to the currentContext which
can accessed immediately - something like: currentContext.get().dirNumLastAccessed = dirNum.
Isn't it?

{noformat}
+            if(ctx.localFS.mkdirs(tmpDir)|| ctx.localFS.exists(tmpDir)) {
{noformat}
Shouldn't we check dir exists first then mkdir if not?


> 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-10048.005.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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