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https://issues.apache.org/jira/browse/HDFS-5453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13854622#comment-13854622
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Suresh Srinivas commented on HDFS-5453:
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bq. But we have been debating internally whether an AbstractNameSystem should 
have those locks...
This beats me. Why would AbstractNameSystem have locks? The locking is a need 
of concrete implementations.

> Support fine grain locking in FSNamesystem
> ------------------------------------------
>
>                 Key: HDFS-5453
>                 URL: https://issues.apache.org/jira/browse/HDFS-5453
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: namenode
>    Affects Versions: 2.0.0-alpha, 3.0.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>
> The namesystem currently uses a course grain lock to control access.  This 
> prevents concurrent writers in different branches of the tree, and prevents 
> readers from accessing branches that writers aren't using.
> Features that introduce latency to namesystem operations, such as cold 
> storage of inodes, will need fine grain locking to avoid degrading the entire 
> namesystem's throughput.



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