Xianyin Xin created YARN-4134:
---------------------------------
Summary: 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
/ \
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.
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