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From "Vinayakumar B (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9952) Expose FSNamesystem lock wait time as metrics
Date Fri, 18 Mar 2016 02:58:33 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9952?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15200902#comment-15200902
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Vinayakumar B commented on HDFS-9952:
-------------------------------------

{quote}In this case, the time frame of holding MutableRate lock is short. What it does inside
the lock is simple algebraic calculation. But assume fsWriteLock is just released, and many
threads are waiting at the entrance of fsReadLock. If MutableRate lock is the first thing
inside the door of fsReadLock, then there's lots contention for MutableRate lock once those
threads get inside the door at the same time.
What if we save the value at ThreadLocal, and after we release the fsReadLock, we add it to
metrics? ThreadLocal is lock free.{quote}
Thanks for the pointers [~walter.k.su].

Updated the patch.

> Expose FSNamesystem lock wait time as metrics
> ---------------------------------------------
>
>                 Key: HDFS-9952
>                 URL: https://issues.apache.org/jira/browse/HDFS-9952
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Vinayakumar B
>            Assignee: Vinayakumar B
>         Attachments: HDFS-9952-01.patch, HDFS-9952-02.patch, HDFS-9952-03.patch
>
>
> Expose FSNameSystem's readlock() and writeLock() wait time as metrics.



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