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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-3633) With Fair Scheduler, cluster can logjam when there are too many queues
Date Wed, 13 May 2015 22:37:01 GMT

    [ https://issues.apache.org/jira/browse/YARN-3633?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14542855#comment-14542855
] 

Karthik Kambatla commented on YARN-3633:
----------------------------------------

Thanks for reporting this, Rohit. 

Extrapolating the example, consider the applications' containers also need 3 GB. With the
proposed change, the AMs would come up but will not be able to run any containers. Note that
this is only an issue on a cluster where a single AM fills up the am-share; is this likely
to happen on larger clusters and production deployments?

The scheduler could realize there aren't enough resources to run applications from multiple
queues and run them in some order, but that would violate the fairness policies. 

> With Fair Scheduler, cluster can logjam when there are too many queues
> ----------------------------------------------------------------------
>
>                 Key: YARN-3633
>                 URL: https://issues.apache.org/jira/browse/YARN-3633
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: fairscheduler
>    Affects Versions: 2.6.0
>            Reporter: Rohit Agarwal
>            Assignee: Rohit Agarwal
>            Priority: Critical
>
> It's possible to logjam a cluster by submitting many applications at once in different
queues.
> For example, let's say there is a cluster with 20GB of total memory. Let's say 4 users
submit applications at the same time. The fair share of each queue is 5GB. Let's say that
maxAMShare is 0.5. So, each queue has at most 2.5GB memory for AMs. If all the users requested
AMs of size 3GB - the cluster logjams. Nothing gets scheduled even when 20GB of resources
are available.



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