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From "Robert Joseph Evans (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-3274) Race condition in MR App Master Preemtion can cause a dead lock
Date Wed, 26 Oct 2011 20:53:33 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-3274?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13136362#comment-13136362
] 

Robert Joseph Evans commented on MAPREDUCE-3274:
------------------------------------------------

>From what I can see in the code.  The simplest thing to do appears to be inside AssignedRequests.add
check preemptionWaitingReduces, when assigning the container, and then if it is there, re-issue
the TA_KILL event.

I am not sure that this is the correct thing to do, as a TA_KILL has already been issued.
 I will try to trace down the events associated with these.
                
> Race condition in MR App Master Preemtion can cause a dead lock
> ---------------------------------------------------------------
>
>                 Key: MAPREDUCE-3274
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3274
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2, scheduler
>    Affects Versions: 0.23.0, 0.24.0
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
>            Priority: Critical
>             Fix For: 0.23.0, 0.24.0
>
>
> There appears to be a race condition in the MR App Master in relation to preempting reducers
to let a mapper run.  In the particular case that I have been debugging a reducer was selected
for preemption that did not have a container assigned to it yet. When the container became
available that reduce started running and the previous TA_KILL event appears to have been
ignored.

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