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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5242) Reduce contention on DatanodeInfo instances
Date Mon, 16 Dec 2013 21:54:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13849771#comment-13849771
] 

Suresh Srinivas commented on HDFS-5242:
---------------------------------------

I am not sure how much performance impact this synchronization has. Do you have have numbers
about the impact of this change?

bq. As mentioned in the first comment, the set is called only once at DN registration so there
is actually no race to avoid.
@Daryn, I think if a setter is called by one thread and getter is called by another, then
synchronized is still needed. Without that it is possible that another thread may never see
the changed value.


> Reduce contention on DatanodeInfo instances
> -------------------------------------------
>
>                 Key: HDFS-5242
>                 URL: https://issues.apache.org/jira/browse/HDFS-5242
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>    Affects Versions: 2.0.0-alpha, 3.0.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>         Attachments: HDFS-5242.patch
>
>
> Synchronization in {{DatanodeInfo}} instances causes unnecessary contention between call
handlers.



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