[jira] [Created] (YARN-4975) Fair Scheduler: exception thrown when a parent queue marked 'parent' has configured child queues

["Ashwin Shankar (JIRA)" <ji...@apache.org>]

Ashwin Shankar created YARN-4975:
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             Summary: Fair Scheduler: exception thrown when a parent queue marked 'parent' has configured child queues
                 Key: YARN-4975
                 URL: https://issues.apache.org/jira/browse/YARN-4975
             Project: Hadoop YARN
          Issue Type: Bug
          Components: fairscheduler
    Affects Versions: 2.7.2
            Reporter: Ashwin Shankar


We upgraded our clusters to 2.7.2 from 2.4.1 and saw the following exception in RM logs :
{code}
Caused by: org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.AllocationConfigurationException: Both <reservation> and type="parent" found for queue root.adhoc which is unsupported
        at
org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.AllocationFileLoaderService.loadQueue(AllocationFileLoaderService.java:519)
        at org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.AllocationFileLoaderService.reloadAllocations(AllocationFileLoaderService.java:352)
        at org.apache.hadoop.yarn.server.resourcemanager.scheduler.fair.FairScheduler.initScheduler(FairScheduler.java:1440)
{code}

>From the exception, it looks like we've configured 'reservation', but we've not. The issue is that AllocationFileLoaderService#loadQueue assumes that a parent queue cannot be marked as 'type=parent' if it has configured child queues. That can be a problem in cases where we mark a queue as 'parent' which has no configured child queues to start with, but we can add child queues later on.
Also the exception is kind of misleading since we haven't configured 'reservation'. 

How to reproduce:
Run fair scheduler with following queue config:
{code}
<queue name="p" type="parent">
        <weight>10</weight>
        <maxRunningApps>300</maxRunningApps>
        <queue name="c">
            <weight>3</weight>
         </queue>
</queue>
{code}




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