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From "Edward Bortnikov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5453) Support fine grain locking in FSNamesystem
Date Mon, 18 Nov 2013 21:33:22 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13825798#comment-13825798
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Edward Bortnikov commented on HDFS-5453:
----------------------------------------

We work with Daryn on this feature. Fine grained locking is crucial when the request implementation
makes a blocking call, e.g., an RPC to a remote block management service. In this setting,
the global lock becomes awful - it's easy to demonstrate. With the current single-process
implementation, there is no visible difference from the global lock, because the request code
executes locally, and is very fast. 

> 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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