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From "kyungwan nam (JIRA)" <j...@apache.org>
Subject [jira] [Created] (YARN-8020) when DRF is used, preemption does not trigger due to incorrect idealAssigned
Date Sat, 10 Mar 2018 04:52:00 GMT
kyungwan nam created YARN-8020:
----------------------------------

             Summary: when DRF is used, preemption does not trigger due to incorrect idealAssigned
                 Key: YARN-8020
                 URL: https://issues.apache.org/jira/browse/YARN-8020
             Project: Hadoop YARN
          Issue Type: Bug
            Reporter: kyungwan nam


I’ve met that Inter Queue Preemption does not work.
It happens when DRF is used and submitting application with a large number of vcores.

IMHO, idealAssigned can be set incorrectly by following code.
{code}
// This function "accepts" all the resources it can (pending) and return
// the unused ones
Resource offer(Resource avail, ResourceCalculator rc,
    Resource clusterResource, boolean considersReservedResource) {
  Resource absMaxCapIdealAssignedDelta = Resources.componentwiseMax(
      Resources.subtract(getMax(), idealAssigned),
      Resource.newInstance(0, 0));
  // accepted = min{avail,
  //               max - assigned,
  //               current + pending - assigned,
  //               # Make sure a queue will not get more than max of its
  //               # used/guaranteed, this is to make sure preemption won't
  //               # happen if all active queues are beyond their guaranteed
  //               # This is for leaf queue only.
  //               max(guaranteed, used) - assigned}
  // remain = avail - accepted
  Resource accepted = Resources.min(rc, clusterResource,
      absMaxCapIdealAssignedDelta,
      Resources.min(rc, clusterResource, avail, Resources
          /*
           * When we're using FifoPreemptionSelector (considerReservedResource
           * = false).
           *
           * We should deduct reserved resource from pending to avoid excessive
           * preemption:
           *
           * For example, if an under-utilized queue has used = reserved = 20.
           * Preemption policy will try to preempt 20 containers (which is not
           * satisfied) from different hosts.
           *
           * In FifoPreemptionSelector, there's no guarantee that preempted
           * resource can be used by pending request, so policy will preempt
           * resources repeatly.
           */
          .subtract(Resources.add(getUsed(),
              (considersReservedResource ? pending : pendingDeductReserved)),
              idealAssigned)));
{code}

let’s say,

* cluster resource : <Memory:200GB, VCores:20>
* idealAssigned(assigned): <Memory:100GB, VCores:10>
* avail: <Memory:181GB, Vcores:1>
* current: <Memory:19GB, Vcores:19>
* pending: <Memory:0, Vcores:0>

current + pending - assigned: <Memory:-181GB, Vcores:9>
min ( avail, (current + pending - assigned) ) : <Memory:-181GB, Vcores:9>
accepted: <Memory:-181GB, Vcores:9>

as a result, idealAssigned will be <Memory:-81GB, VCores:19>, which does not trigger
preemption.



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