Peng Zhang created YARN-3414:
--------------------------------

             Summary: FairScheduler's preemption may cause livelock
                 Key: YARN-3414
                 URL: https://issues.apache.org/jira/browse/YARN-3414
             Project: Hadoop YARN
          Issue Type: Bug
          Components: fairscheduler
    Affects Versions: 2.6.0
            Reporter: Peng Zhang


I met this problem in our cluster, it cause livelock during preemption and 
scheduling.

Queue hierarchy described as below:
{noformat}
                      root
              /        |        \
          queue-1    queue-2    queue-3     
          /    \
queue-1-1      queue-1-2
{noformat}
# Assume cluster resource is 100G in memory
# Assume queue-1 has max resource limit 20G
# queue-1-1 is active and it will get max 20G memory(equal to its fairshare)
# queue-2 is active then, and it require 30G memory(less than its fairshare)
# queue-3 is active, and it can be assigned with all other resources, 50G 
memory(larger than its fairshare). At here three queues' fair share is (20, 40, 
40), and usage is (20, 30, 50)
# queue-1-2 is active, it will cause new preemption request(10G memory and 
intuitively it can only preempt from its sibling queue-1-1)
# Actually preemption starts from root, and it will find queue-3 is most over 
fairshare, and preempt some resources form queue-3.
# But during scheduling, it will find queue-1 itself arrived it's max 
fairshare, and cannot assign resource to it. Then resource's again assigned to 
queue-3
And then it repeats between last two steps.



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