[jira] [Created] (YARN-6956) preemption may only consider resource requests for one node

["Steven Rand (JIRA)" <ji...@apache.org>]

Steven Rand created YARN-6956:
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             Summary: 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


I'm observing the following series of events on a CDH 5.11.0 cluster, which seem to be possible after https://issues.apache.org/jira/browse/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 cause 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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