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https://issues.apache.org/jira/browse/YARN-4002?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15203611#comment-15203611
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Rohith Sharma K S commented on YARN-4002:
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Thanks [~leftnoteasy] for the looking at the patch..
I was thought about adding these 2 places readlock, but after looking into
caller of these 2 methods I felt it is not really required.
# Method {{setDecomissionedNMsMetrics}} is called during service init, so this
will be called during service initialization.
# Method {{printConfiguredHosts }} is called during service init and
refreshNodes.
## Once again, for service init, I do not think we need really acquire readlock.
## For refresh Node,{{printConfiguredHosts }} is with in the write lock, it is
safe enough to go without read lock.
As of now, without acquiring read lock would not cause any problem. In future,
if any new method calling these methods need to think of acquiring read lock.
> make ResourceTrackerService.nodeHeartbeat more concurrent
> ---------------------------------------------------------
>
> Key: YARN-4002
> URL: https://issues.apache.org/jira/browse/YARN-4002
> Project: Hadoop YARN
> Issue Type: Improvement
> Reporter: Hong Zhiguo
> Assignee: Hong Zhiguo
> Priority: Critical
> Attachments: 0001-YARN-4002.patch, YARN-4002-lockless-read.patch,
> YARN-4002-rwlock.patch, YARN-4002-v0.patch
>
>
> We have multiple RPC threads to handle NodeHeartbeatRequest from NMs. By
> design the method ResourceTrackerService.nodeHeartbeat should be concurrent
> enough to scale for large clusters.
> But we have a "BIG" lock in NodesListManager.isValidNode which I think it's
> unnecessary.
> First, the fields "includes" and "excludes" of HostsFileReader are only
> updated on "refresh nodes". All RPC threads handling node heartbeats are
> only readers. So RWLock could be used to alow concurrent access by RPC
> threads.
> Second, since he fields "includes" and "excludes" of HostsFileReader are
> always updated by "reference assignment", which is atomic in Java, the reader
> side lock could just be skipped.
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