[YARN-5540] scheduler spends too much time looking at empty priorities

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.7.2
• Fix Version/s: 2.8.0, 2.7.4, 3.0.0-alpha2
• Component/s: capacity scheduler, fairscheduler, resourcemanager
• Target Version/s: 2.7.4
• Hadoop Flags: Reviewed
• Assignee: Jason Darrell Lowe
• Reporter: Nathan Roberts
• Created: 19/Aug/16 18:30
• Updated: 19/Sep/16 21:43
• Resolved: 19/Sep/16 20:41

Description

We're starting to see the capacity scheduler run out of scheduling horsepower when running 500-1000 applications on clusters with 4K nodes or so.

This seems to be amplified by TEZ applications. TEZ applications have many more priorities (sometimes in the hundreds) than typical MR applications and therefore the loop in the scheduler which examines every priority within every running application, starts to be a hotspot. The priorities appear to stay around forever, even when there is no remaining resource request at that priority causing us to spend a lot of time looking at nothing.

jstack snippet:

"ResourceManager Event Processor" #28 prio=5 os_prio=0 tid=0x00007fc2d453e800 nid=0x22f3 runnable [0x00007fc2a8be2000]
   java.lang.Thread.State: RUNNABLE
        at org.apache.hadoop.yarn.server.resourcemanager.scheduler.SchedulerApplicationAttempt.getResourceRequest(SchedulerApplicationAttempt.java:210)
        - eliminated <0x00000005e73e5dc0> (a org.apache.hadoop.yarn.server.resourcemanager.scheduler.common.fica.FiCaSchedulerApp)
        at org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue.assignContainers(LeafQueue.java:852)
        - locked <0x00000005e73e5dc0> (a org.apache.hadoop.yarn.server.resourcemanager.scheduler.common.fica.FiCaSchedulerApp)
        - locked <0x00000003006fcf60> (a org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue)
        at org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.ParentQueue.assignContainersToChildQueues(ParentQueue.java:527)
        - locked <0x00000003001b22f8> (a org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.ParentQueue)
        at org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.ParentQueue.assignContainers(ParentQueue.java:415)
        - locked <0x00000003001b22f8> (a org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.ParentQueue)
        at org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler.allocateContainersToNode(CapacityScheduler.java:1224)
        - locked <0x0000000300041e40> (a org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler)