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https://issues.apache.org/jira/browse/HADOOP-12475?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14959864#comment-14959864
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Sangjin Lee commented on HADOOP-12475:
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Thanks much for the detailed explanation! It would be awesome if that is in
[the how-to-commit wiki page|https://wiki.apache.org/hadoop/HowToCommit]. It
seems like I don't have the permission to edit it. I'd greatly appreciate it if
you could add that to the wiki page. Thanks again!
> Replace guava Cache with ConcurrentHashMap for caching Connection in ipc
> Client
> -------------------------------------------------------------------------------
>
> Key: HADOOP-12475
> URL: https://issues.apache.org/jira/browse/HADOOP-12475
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: conf, io, ipc
> Reporter: Walter Su
> Assignee: Walter Su
> Fix For: 2.8.0
>
> Attachments: HADOOP-12475.01.patch, HADOOP-12475.02.patch,
> HADOOP-12475.03.patch
>
>
> quote [~daryn] from HADOOP-11772:
> {quote}
> CacheBuilder is obscenely expensive for concurrent map, and it requires
> generating unnecessary garbage even just to look up a key. Replace it with
> ConcurrentHashMap.
> I identified this issue that impaired my own perf testing under load. The
> slowdown isn't just the sync. It's the expensive of Connection's ctor
> stalling other connections. The expensive of ConnectionId#equals causes
> delays. Synch'ing on connections causes unfair contention unlike a sync'ed
> method. Concurrency simply hides this.
> {quote}
> BTW, guava Cache is heavyweight. Per local test, ConcurrentHashMap has better
> overal performance.
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