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From "Xianyin Xin (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (YARN-4134) FairScheduler preemption stops at queue level that all child queues are not over their fairshare
Date Wed, 09 Sep 2015 09:38:45 GMT

     [ https://issues.apache.org/jira/browse/YARN-4134?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Xianyin Xin updated YARN-4134:
------------------------------
    Description: 
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.

  was:
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
      /    \
queue1.3, (  queue1.4  )
{code}
suppose there're 8 containers, and queues at any level have the same weight. queue1.3 takes
4 and queue2 takes 4, so both queue1 and queue2 are at their fairshare. Now we submit an app
in queue1.4 with 4 containers needs, it should preempt 2 from queue1.3, but the candidate-containers
selection procedure will stop at level that all of the child queues are not over their fairshare,
and none of the containers will be preempted.


> 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
>
> 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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