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https://issues.apache.org/jira/browse/YARN-3091?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16244191#comment-16244191
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Jason Lowe commented on YARN-3091:
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bq. I'm looking at reverting the read/write lock changes within the fair 
scheduler at least. Thoughts?

+1, we've also seen a number of problems around the scheduler's read/write 
locks and have done some short-term fixes to work around them like YARN-6680.  
They are significantly more expensive to acquire than a standard mutex if 
nobody is holding the lock, and there are lots of places where the scheduler 
needs to acquire them during a scheduling pass.


> [Umbrella] Improve and fix locks of RM scheduler
> ------------------------------------------------
>
>                 Key: YARN-3091
>                 URL: https://issues.apache.org/jira/browse/YARN-3091
>             Project: Hadoop YARN
>          Issue Type: Task
>          Components: capacityscheduler, fairscheduler, resourcemanager, 
> scheduler
>            Reporter: Wangda Tan
>
> In existing YARN RM scheduler, there're some issues of using locks. For 
> example:
> - Many unnecessary synchronized locks, we have seen several cases recently 
> that too frequent access of scheduler makes scheduler hang. Which could be 
> addressed by using read/write lock. Components include scheduler, CS queues, 
> apps
> - Some fields not properly locked (Like clusterResource)
> We can address them together in this ticket.
> (More details see comments below)



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