[jira] [Commented] (YARN-3633) With Fair Scheduler, cluster can logjam when there are too many queues

["Rohit Agarwal (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/YARN-3633?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14609163#comment-14609163 ] 

Rohit Agarwal commented on YARN-3633:
-------------------------------------

Yes, that is very much possible. But without this change - this scenario will result in none of the applications making any progress. I would take one application getting starved over the whole cluster getting starved any day. :-)

FWIW, we have been running our clusters with this patch for a month now and haven't seen any cluster logjam since.

> 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
>         Attachments: YARN-3633-1.patch, YARN-3633.patch
>
>
> 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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