Ram Venkatesh created YARN-2362:

             Summary: Capacity Scheduler apps with requests that exceed 
capacity can starve pending apps
                 Key: YARN-2362
                 URL: https://issues.apache.org/jira/browse/YARN-2362
             Project: Hadoop YARN
          Issue Type: Bug
          Components: capacityscheduler
    Affects Versions: 2.4.1
            Reporter: Ram Venkatesh

Cluster configuration:
Total memory: 8GB
yarn.scheduler.minimum-allocation-mb 256
yarn.scheduler.capacity.maximum-am-resource-percent 1 (100%, test only config)

App 1 makes a request for 4.6 GB, succeeds, app transitions to RUNNING state. 
It subsequently makes a request for 4.6 GB, which cannot be granted and it 

App 2 makes a request for 1 GB - never receives it, so the app stays in the 
ACCEPTED state for ever.

I think this can happen in leaf queues that are near capacity.

The fix is likely in LeafQueue.java assignContainers near line 861, where it 
returns if the assignment would exceed queue capacity, instead of checking if 
requests for other active applications can be met.

           // Check queue max-capacity limit
           if (!assignToQueue(clusterResource, required)) {
-            return NULL_ASSIGNMENT;
+            break;

With this change, the scenario above allows App 2 to start and finish while App 
1 continues to wait.

I have a patch available, but wondering if the current behavior is by design.

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