This problem is due to
YARN-4280, parent queue will deduct child queue's headroom when the child queue reached its resource limit and the skipped type is QUEUE_LIMIT, the resource limits of deepest parent queue will be correctly calculated, but for non-deepest parent queue, its headroom may be much more than the sum of reached-limit child queues' headroom, so that the resource limit of non-deepest parent may be much less than its true value and block the allocation for later queues.
To reproduce this problem with UT:
(1) Cluster has two nodes whose node resource both are <10GB, 10core> and 3-level queues as below, among them max-capacity of "c1" is 10 and others are all 100, so that max-capacity of queue "c1" is <2GB, 2core>
(2) Submit app1 to queue "c1" and launch am1(resource=<1GB, 1 core>) on nm1
(3) Submit app2 to queue "b" and launch am2(resource=<1GB, 1 core>) on nm1
(4) app1 and app2 both ask one <2GB, 1core> containers.
(5) nm1 do 1 heartbeat
Now queue "c" has lower capacity percentage than queue "b", the allocation sequence will be "a" -> "c" -> "b",
queue "c1" has reached queue limit so that requests of app1 should be pending,
headroom of queue "c1" is <1GB, 1core> (=max-capacity - used),
headroom of queue "c" is <18GB, 18core> (=max-capacity - used),
after allocation for queue "c", resource limit of queue "b" will be wrongly calculated as <2GB, 2core>,
headroom of queue "b" will be <1GB, 1core> (=resource-limit - used)
so that scheduler won't allocate one container for app2 on nm1