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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:
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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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