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https://issues.apache.org/jira/browse/YARN-3390?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14508121#comment-14508121
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Sangjin Lee commented on YARN-3390:
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bq. In TimelineCollectorManager, I'm still having this question, although we
may not want to address it in this JIRA: are there any special consistency
requirements that prevent us from using ConcurrentHashMap?
I can answer this as I added that code. :) In putIfAbsent(), it needs to start
the collector as well if get() returns null. If we used ConcurrentHashMap and
removed synchronization, multiple threads could start their own collectors
unnecessarily. It is probably not a show stopper but less than desirable. Also,
in real life the contention on TimelineCollectorManager is low enough that
synchronization should be perfectly adequate. If we want to do this without
synchronization, then we would want to use something like guava's LoadingCache.
> Reuse TimelineCollectorManager for RM
> -------------------------------------
>
> Key: YARN-3390
> URL: https://issues.apache.org/jira/browse/YARN-3390
> Project: Hadoop YARN
> Issue Type: Sub-task
> Components: timelineserver
> Reporter: Zhijie Shen
> Assignee: Zhijie Shen
> Attachments: YARN-3390.1.patch
>
>
> RMTimelineCollector should have the context info of each app whose entity
> has been put
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