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From "Edward Bortnikov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5453) Support fine grain locking in FSNamesystem
Date Wed, 18 Dec 2013 13:32:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13851722#comment-13851722
] 

Edward Bortnikov commented on HDFS-5453:
----------------------------------------

Fine grained locking will not expected to have positive performance impact with a single-process
namenode implementation. The execution of every API is so short that it does not justify acquisition
of fine-grained locks along the path (we have evaluated the performance). 

Fine grained locking makes sense (and is a crucial feature) in the context of block management
as a service 
(see https://issues.apache.org/jira/browse/HDFS-5477). When block management is an external
process, the NN cannot afford holding a global lock during the RPC. 

> 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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