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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14912) FairCallQueue may defer servicing calls
Date Wed, 27 Sep 2017 21:19:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14912?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16183268#comment-16183268
] 

Daryn Sharp commented on HADOOP-14912:
--------------------------------------

In practice the impact isn't severe.  The next call will dislodge one of the "stuck" queued
calls.  Latency is affected to some degree, but is skewed towards increased latency for lower
priority buckets.  Across multiple production clusters, the number of lost permits is usually
low single digit.  

> FairCallQueue may defer servicing calls
> ---------------------------------------
>
>                 Key: HADOOP-14912
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14912
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: ipc
>    Affects Versions: 2.8.2
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>
> HADOOP-14033 switched a lock to a semaphore to allow concurrency for producers &
consumers to the underlying queues.  A race condition was created that may cause a consumer
to acquire a permit but not extract an element, leaving the semaphore with fewer permits than
queued elements.  This causes a minimum number of calls to always be present in the call queue.



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