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https://issues.apache.org/jira/browse/HADOOP-13189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15322007#comment-15322007
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Ming Ma commented on HADOOP-13189:
----------------------------------

Thanks [~shv], [~redvine]. That seems reasonable. Although in actual setup, we 
haven't run into any issue or we have accounted for the factor. Another thing, 
if RPC backoff is enabled and all users fall under highest priority queue, 
equal divide means smaller capacity for the highest priority queue and thus got 
backoff sooner than the configured queue size.

> FairCallQueue makes callQueue larger than the configured capacity.
> ------------------------------------------------------------------
>
>                 Key: HADOOP-13189
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13189
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: ipc
>    Affects Versions: 2.6.0
>            Reporter: Konstantin Shvachko
>            Assignee: Vinitha Reddy Gankidi
>         Attachments: HADOOP-13189.001.patch, HADOOP-13189.002.patch, 
> HADOOP-13189.003.patch
>
>
> {{FairCallQueue}} divides {{callQueue}} into multiple (4 by default) 
> sub-queues, with each sub-queue corresponding to a different level of 
> priority. The constructor for {{FairCallQueue}} takes the same parameter 
> {{capacity}} as the default CallQueue implementation, and allocates all its 
> sub-queues of size {{capacity}}. With 4 levels of priority (sub-queues) by 
> default it results in the total callQueue size 4 times larger than it should 
> be based on the configuration.
> {{capacity}} should be divided by the number of sub-queues at some place.



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