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https://issues.apache.org/jira/browse/YARN-4134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14742795#comment-14742795
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Xianyin Xin commented on YARN-4134:
-----------------------------------
Just found this issue duplicated YARN-3405, but the two has different
solutions. Since this issue would be addressed in YARN-2154, link them together.
> FairScheduler preemption stops at queue level that all child queues are not
> over their fairshare
> ------------------------------------------------------------------------------------------------
>
> Key: YARN-4134
> URL: https://issues.apache.org/jira/browse/YARN-4134
> Project: Hadoop YARN
> Issue Type: Bug
> Components: fairscheduler
> Reporter: Xianyin Xin
> Assignee: Xianyin Xin
> Attachments: YARN-4134.001.patch, YARN-4134.002.patch,
> YARN-4134.003.patch
>
>
> Now FairScheudler uses a choose-a-candidate method to select a container from
> leaf queues that to be preempted, in {{FSParentQueue.preemptContainer()}},
> {code}
> readLock.lock();
> try {
> for (FSQueue queue : childQueues) {
> if (candidateQueue == null ||
> comparator.compare(queue, candidateQueue) > 0) {
> candidateQueue = queue;
> }
> }
> } finally {
> readLock.unlock();
> }
> // Let the selected queue choose which of its container to preempt
> if (candidateQueue != null) {
> toBePreempted = candidateQueue.preemptContainer();
> }
> {code}
> a candidate child queue is selected. However, if the queue's usage isn't over
> it's fairshare, preemption will not happen:
> {code}
> if (!preemptContainerPreCheck()) {
> return toBePreempted;
> }
> {code}
> A scenario:
> {code}
> root
> / \
> queue1 queue2
> / \
> queue2.3, ( queue2.4 )
> {code}
> suppose there're 8 containers, and queues at any level have the same weight.
> queue1 takes 4 and queue2.3 takes 4, so both queue1 and queue2 are at their
> fairshare. Now we submit an app in queue2.4 with 4 containers needs, it
> should preempt 2 from queue2.3, but the candidate-containers selection
> procedure will stop at queue1, so none of the containers will be preempted.
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