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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-3655) FairScheduler: potential livelock due to maxAMShare limitation and container reservation
Date Fri, 05 Jun 2015 16:07:01 GMT

    [ https://issues.apache.org/jira/browse/YARN-3655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14574746#comment-14574746
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Karthik Kambatla commented on YARN-3655:
----------------------------------------

Thanks for the clarifications, Zhihai. The latest patch looks mostly good, nice test. Few
nit picks before we get this in:
# In hasContainerForNode, the patch has some spurious changes. Also, would be nice to add
a comment for the newly added check.
# File a follow-up JIRA to separate out the code paths for assigning a reserved container
and a non-reserved container. 
# File a follow-up JIRA to move all reservation-related tests from TestFairScheduler to TestFairSchedulerReservations

> FairScheduler: potential livelock due to maxAMShare limitation and container reservation

> -----------------------------------------------------------------------------------------
>
>                 Key: YARN-3655
>                 URL: https://issues.apache.org/jira/browse/YARN-3655
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: fairscheduler
>    Affects Versions: 2.7.0
>            Reporter: zhihai xu
>            Assignee: zhihai xu
>         Attachments: YARN-3655.000.patch, YARN-3655.001.patch, YARN-3655.002.patch, YARN-3655.003.patch
>
>
> FairScheduler: potential livelock due to maxAMShare limitation and container reservation.
> If a node is reserved by an application, all the other applications don't have any chance
to assign a new container on this node, unless the application which reserves the node assigns
a new container on this node or releases the reserved container on this node.
> The problem is if an application tries to call assignReservedContainer and fail to get
a new container due to maxAMShare limitation, it will block all other applications to use
the nodes it reserves. If all other running applications can't release their AM containers
due to being blocked by these reserved containers. A livelock situation can happen.
> The following is the code at FSAppAttempt#assignContainer which can cause this potential
livelock.
> {code}
>     // Check the AM resource usage for the leaf queue
>     if (!isAmRunning() && !getUnmanagedAM()) {
>       List<ResourceRequest> ask = appSchedulingInfo.getAllResourceRequests();
>       if (ask.isEmpty() || !getQueue().canRunAppAM(
>           ask.get(0).getCapability())) {
>         if (LOG.isDebugEnabled()) {
>           LOG.debug("Skipping allocation because maxAMShare limit would " +
>               "be exceeded");
>         }
>         return Resources.none();
>       }
>     }
> {code}
> To fix this issue, we can unreserve the node if we can't allocate the AM container on
the node due to Max AM share limitation and the node is reserved by the application.



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