Peter Bacsko created YARN-10283:
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Summary: Capacity Scheduler: starvation occurs if a higher
priority queue is full a and node labels are used
Key: YARN-10283
URL: https://issues.apache.org/jira/browse/YARN-10283
Project: Hadoop YARN
Issue Type: Bug
Components: capacity scheduler
Reporter: Peter Bacsko
Assignee: Peter Bacsko
Recently we've been investigating a scenario where applications submitted to a
lower priority queue could not get scheduled because a higher priority queue in
the same hierarchy could now satisfy the allocation request. Both queue
belonged to the same partition.
If we disabled node labels, the problem disappeared.
The problem is that {{RegularContainerAllocator}} always allocated a container
for the request, even if it should not have.
*Example:*
* Cluster total resources: 3 nodes, 15GB, 24 vcores
* Partition "shared" was created with 2 nodes
* "root.lowprio" (priority = 20) and "root.highprio" (priorty = 40) were added
to the partition
* Both queues have a limit of <memory:5120, vCores:8>
* Using DominantResourceCalculator
Setup:
Submit distributed shell application to highprio with switches "-num_containers
3 -container_vcores 4". The memory allocation is 512MB per container.
Chain of events:
1. Queue is filled with contaners until it reaches usage <memory:2560, vCores:5>
2. A node update event is pushed to CS from a node which is part of the
partition
2. {{AbstractCSQueue.canAssignToQueue()}} returns true because it's smaller
than the current limit resource <memory:5120, vCores:8>
3. Then {{LeafQueue.assignContainers()}} runs successfully and gets an
allocated container for <memory:512, vcores:4>
4. But we can't commit the resource request because we would have 9 vcores in
total, violating the limit.
The problem is that we always try to assign container for the same application
in each heartbeat from "highprio". Applications in "lowprio" cannot make
progress.
*Problem:*
{{RegularContainerAllocator.assignContainer()}} does not handle this case well.
We only reject allocation if this condition is satisfied:
{noformat}
if (rmContainer == null && reservationsContinueLooking
&& node.getLabels().isEmpty()) {
{noformat}
But if we have node labels, we succeed with the allocation if there's room for
a container.
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