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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