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From "Steven Rand (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-6956) preemption may only consider resource requests for one node
Date Wed, 06 Sep 2017 01:16:02 GMT

    [ https://issues.apache.org/jira/browse/YARN-6956?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16154671#comment-16154671
] 

Steven Rand commented on YARN-6956:
-----------------------------------

Friendly ping [~kasha] and/or [~templedf]. I'll fix the checkstyle issues in the next patch,
but wanted to gather other feedback as well.

> preemption may only consider resource requests for one node
> -----------------------------------------------------------
>
>                 Key: YARN-6956
>                 URL: https://issues.apache.org/jira/browse/YARN-6956
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: fairscheduler
>    Affects Versions: 2.9.0, 3.0.0-beta1
>         Environment: CDH 5.11.0
>            Reporter: Steven Rand
>            Assignee: Steven Rand
>         Attachments: YARN-6956.001.patch
>
>
> I'm observing the following series of events on a CDH 5.11.0 cluster, which seem to be
possible after YARN-6163:
> 1. An application is considered to be starved, so {{FSPreemptionThread}} calls {{identifyContainersToPreempt}},
and that calls {{FSAppAttempt#getStarvedResourceRequests}} to get a list of {{ResourceRequest}}
instances that are enough to address the app's starvation.
> 2. The first {{ResourceRequest}} that {{getStarvedResourceRequests}} sees is enough to
address the app's starvation, so we break out of the loop over {{appSchedulingInfo.getAllResourceRequests()}}
after only one iteration: https://github.com/apache/hadoop/blob/trunk/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FSAppAttempt.java#L1180.
We return only this one {{ResourceRequest}} back to the {{identifyContainersToPreempt}} method.
> 3. It turns out that this particular {{ResourceRequest}} happens to have a value for
{{getResourceName}} that identifies a specific node in the cluster. This causes preemption
to only consider containers on that node, and not the rest of the cluster.
> [~kasha], does that make sense? I'm happy to submit a patch if I'm understanding the
problem correctly.



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