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https://issues.apache.org/jira/browse/HADOOP-12475?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14958308#comment-14958308
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Sangjin Lee commented on HADOOP-12475:
--------------------------------------
The latest patch looks good for the most part.
A couple of nits: IMO it's generally a good practice to declare types with
interfaces rather than concrete implementations:
{code}
129 private ConcurrentHashMap<ConnectionId, Connection> connections =
130 new ConcurrentHashMap<>();
{code}
I would use {{ConcurrentMap}} instead of {{ConcurrentHashMap}} as the type.
Also line 130 has the checkstyle violation. It'd be good to fix it too.
> 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
> Attachments: HADOOP-12475.01.patch, HADOOP-12475.02.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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