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From "Sangjin Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-12475) Replace guava Cache with ConcurrentHashMap for caching Connection in ipc Client
Date Thu, 15 Oct 2015 23:07:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-12475?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14959815#comment-14959815

Sangjin Lee commented on HADOOP-12475:

Thanks [~cnauroth]!

I'm actually somewhat confused by this. When we commit a patch onto trunk, do we add the attribution
to the trunk section or the latest unreleased major release (in this case 2.8.0)? I see a
whole bunch of JIRAs in both sections, and I assumed that I would add it to the trunk section
for trunk and 2.8.0 for branch-2. The commit guide doesn't seem to mention it clearly either...

> 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

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