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https://issues.apache.org/jira/browse/YARN-9278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16794680#comment-16794680
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Zhaohui Xin commented on YARN-9278:
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[~wilfreds], thanks for your reply. I attached new patch which resolved code
style issues and description in FairScheduler.md.
{quote}We need to get either add some tests or explain why we cannot add tests.
{quote}
I think it's difficult to test because we can't count the number of nodes which
will be preempted. Can you give me some suggestions?
> Shuffle nodes when selecting to be preempted nodes
> --------------------------------------------------
>
> Key: YARN-9278
> URL: https://issues.apache.org/jira/browse/YARN-9278
> Project: Hadoop YARN
> Issue Type: Sub-task
> Components: fairscheduler
> Reporter: Zhaohui Xin
> Assignee: Zhaohui Xin
> Priority: Major
> Attachments: YARN-9278.001.patch, YARN-9278.002.patch,
> YARN-9278.003.patch
>
>
> We should *shuffle* the nodes to avoid some nodes being preempted frequently.
> Also, we should *limit* the num of nodes to make preemption more efficient.
> Just like this,
> {code:java}
> // we should not iterate all nodes, that will be very slow
> long maxTryNodeNum =
> context.getPreemptionConfig().getToBePreemptedNodeMaxNumOnce();
> if (potentialNodes.size() > maxTryNodeNum){
> Collections.shuffle(potentialNodes);
> List<FSSchedulerNode> newPotentialNodes = new ArrayList<FSSchedulerNode>();
> for (int i = 0; i < maxTryNodeNum; i++){
> newPotentialNodes.add(potentialNodes.get(i));
> }
> potentialNodes = newPotentialNodes;
> {code}
>
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