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From "Arpit Agarwal (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HADOOP-12189) CallQueueManager may drop elements from the queue sometimes when calling swapQueue
Date Wed, 08 Jul 2015 18:48:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-12189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14619151#comment-14619151
] 

Arpit Agarwal edited comment on HADOOP-12189 at 7/8/15 6:47 PM:
----------------------------------------------------------------

Hi [~zxu], I am also not sure this issue needs fixing. Dropping some requests in the rare
event of a queue swap looks harmless. I assume clients will experience timeout exceptions
and retry.


was (Author: arpitagarwal):
Hi [~zxu], I am also not sure this issue needs fixing. Dropping some requests during in the
rare event of a queue swap looks harmless. I assume clients will experience timeout exceptions
and retry.

> CallQueueManager may drop elements from the queue sometimes when calling swapQueue
> ----------------------------------------------------------------------------------
>
>                 Key: HADOOP-12189
>                 URL: https://issues.apache.org/jira/browse/HADOOP-12189
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: ipc, test
>    Affects Versions: 2.7.1
>            Reporter: zhihai xu
>            Assignee: zhihai xu
>         Attachments: HADOOP-12189.000.patch, HADOOP-12189.001.patch, HADOOP-12189.none_guarantee.000.patch
>
>
> CallQueueManager may drop elements from the queue sometimes when calling {{swapQueue}}.

> The following test failure from TestCallQueueManager shown some elements in the queue
are dropped.
> https://builds.apache.org/job/PreCommit-HADOOP-Build/7150/testReport/org.apache.hadoop.ipc/TestCallQueueManager/testSwapUnderContention/
> {code}
> java.lang.AssertionError: expected:<27241> but was:<27245>
> 	at org.junit.Assert.fail(Assert.java:88)
> 	at org.junit.Assert.failNotEquals(Assert.java:743)
> 	at org.junit.Assert.assertEquals(Assert.java:118)
> 	at org.junit.Assert.assertEquals(Assert.java:555)
> 	at org.junit.Assert.assertEquals(Assert.java:542)
> 	at org.apache.hadoop.ipc.TestCallQueueManager.testSwapUnderContention(TestCallQueueManager.java:220)
> {code}
> It looked like the elements in the queue are dropped due to {{CallQueueManager#swapQueue}}
> Looked at the implementation of {{CallQueueManager#swapQueue}}, there is a possibility
that the elements in the queue are dropped. If the queue is full, the calling thread for {{CallQueueManager#put}}
is blocked for long time. It may put the element into the old queue after queue in {{takeRef}}
is changed by swapQueue, then this element in the old queue will be dropped.



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