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https://issues.apache.org/jira/browse/YARN-9278?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16776184#comment-16776184
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Yufei Gu commented on YARN-9278:
--------------------------------

bq. If our cluster has a lot of long-running jobs, the above method is not 
helpful. 
That's unfortunate.

Setting a maximum num of nodes to iterate seems a quick-and-dirty way to solve 
the latency in big clusters. Let's brainstorm the solution. [~Steven Rand] and 
[~wilfreds], what do you think?

> 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
>
> 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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