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https://issues.apache.org/jira/browse/YARN-4002?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15174833#comment-15174833
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Rohith Sharma K S commented on YARN-4002:
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All the method in HostsFileReader are synchronized. And method {{isValidNode}}
does 2 separate calls to hostsReader. There could be a scenario (if lock is not
used) where after executing {{hostsReader.getHosts();}} , hostreader can do
refresh which gives updated result for {{hostsReader.getExcludedHosts();}} but
stale host details for getHosts method. Lockless read might mix up old and new
values which is incorrect.
> 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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