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https://issues.apache.org/jira/browse/HADOOP-13742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15655437#comment-15655437
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Kihwal Lee commented on HADOOP-13742:
-------------------------------------

First of all, the use of "Vs" is probably not the best choice. "Vs" is for two 
comparable things.

I am wondering whether introducing a separate metrics class is better. 
(Something similar to {{RpcDetailedMetrics}})  For typical metrics, a counter 
is simply incremented and the diff shows the rate. If users are only interested 
in instantaneous counts and do not care at all about cumulative counts, the 
approach in the patch might be okay.  But I am thinking cumulative values are 
useful too.  

If we are to proceed with the proposed approach, I suggest simply synchronize 
on the lock object inside {{incrUserConnections()}} and 
{{decrUserConnections()}} and lose the private methods. Then no need to have 
{{AtomicInteger}}.  The ideal way will be range-locking the map, but I don't 
know whether there is any known good implementation of it. In any case, the 
number of rpc reader threads is typically small, so this level of 
synchronization/monitor lock should be okay.

> Expose "NumOpenConnectionsPerUser" as a metric
> ----------------------------------------------
>
>                 Key: HADOOP-13742
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13742
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Brahma Reddy Battula
>            Assignee: Brahma Reddy Battula
>         Attachments: HADOOP-13742-002.patch, HADOOP-13742-003.patch, 
> HADOOP-13742-004.patch, HADOOP-13742.patch
>
>
> To track user level connections( How many connections for each user) in busy 
> cluster where so many connections to server.



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