Szilard Nemeth reassigned YARN-8951:

    Assignee:     (was: Szilard Nemeth)

> Defining default queue placement rule in allocations file with create="false" 
> throws an NPE
> -------------------------------------------------------------------------------------------
>                 Key: YARN-8951
>                 URL: https://issues.apache.org/jira/browse/YARN-8951
>             Project: Hadoop YARN
>          Issue Type: Bug
>            Reporter: Szilard Nemeth
>            Priority: Major
>         Attachments: default-placement-rule-with-create-false.patch
> If the default queue placement rule is defined with {{create="false"}} and a 
> scheduling request is created for queue {{"root.default"}}, then 
> {{FairScheduler#assignToQueue}} throws an NPE, while trying to construct an 
> error message in the catch block of {{IllegalStateException}}, relying on the 
> fact that the {{rmApp}} is not null but it is.
> Example of such a config file:
> {code:java}
> <?xml version="1.0"?>
> <allocations>
>       <queue name="parentq" type="parent">
>               <minResources>1024mb,0vcores</minResources>
>       </queue>
>       <queuePlacementPolicy>
>               <rule name="default" create="false"/>
>       </queuePlacementPolicy>
> </allocations>
> {code}
> This is suspicious, as there are some null checks for {{rmApp}} in the same 
> method.
>  Not sure if this is a special case for the tests or it is reproducable in a 
> cluster, this needs further investigation.
> In any case, it's not good that we try to dereference the {{rmApp}} that is 
> null.
> On the other hand, I'm not sure if the default queue placement rule with 
> {{create="false"}} makes sense at all. Looking at the documentation 
> ([https://hadoop.apache.org/docs/r3.1.0/hadoop-yarn/hadoop-yarn-site/FairScheduler.html):]
> {quote}default: the app is placed into the queue specified in the ‘queue’ 
> attribute of the default rule. *If ‘queue’ attribute is not specified, the 
> app is placed into ‘root.default’ queue.*
> A queuePlacementPolicy element: which contains a list of rule elements that 
> tell the scheduler how to place incoming apps into queues. Rules are applied 
> in the order that they are listed. Rules may take arguments. *All rules 
> accept the “create” argument, which indicates whether the rule can create a 
> new queue. “Create” defaults to true; if set to false and the rule would 
> place the app in a queue that is not configured in the allocations file, we 
> continue on to the next rule.* The last rule must be one that can never issue 
> a continue....
> {quote}
> In this case, the rule has the queue property suppressed so the apps should 
> be placed to the {{root.default}} queue (which is an undefined queue 
> according to the config file), and create is false, meaning that the queue 
> {{root.default}} cannot be created at all.
> *This seems to be a case of an invalid queue configuration file for me.*
> [~jlowe], [~leftnoteasy]: What is your take on this?

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