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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-7295) Contention in HBaseClient.getConnection
Date Mon, 10 Dec 2012 21:55:21 GMT

    [ https://issues.apache.org/jira/browse/HBASE-7295?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13528331#comment-13528331
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Lars Hofhansl commented on HBASE-7295:
--------------------------------------

Thanks Varun.

Double checked locking only works correctly if the checked object/value is declared volatile.
Otherwise the JVM is free (1) to reorder the statements and (2) not provide the latest value
to the current thread. This describes it reasonably well http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html
(you probably saw this, just in case)

I agree it'll make it slower again, need to performance test.

                
> Contention in HBaseClient.getConnection
> ---------------------------------------
>
>                 Key: HBASE-7295
>                 URL: https://issues.apache.org/jira/browse/HBASE-7295
>             Project: HBase
>          Issue Type: Improvement
>    Affects Versions: 0.94.3
>            Reporter: Varun Sharma
>            Assignee: Varun Sharma
>             Fix For: 0.96.0, 0.94.4
>
>         Attachments: 7295-0.94.txt, 7295-0.94-v2.txt, 7295-0.94-v3.txt, 7295-0.94-v4.txt,
7295-trunk.txt, 7295-trunk.txt, 7295-trunk-v2.txt
>
>
> HBaseClient.getConnection() synchronizes on the connections object. We found severe contention
on a thrift gateway which was fanning out roughly 3000+ calls per second to hbase region servers.
The thrift gateway had 2000+ threads for handling incoming connections. Threads were blocked
on the syncrhonized block - we set ipc.pool.size to 200. Since we are using RoundRobin/ThreadLocal
pool only - its not necessary to synchronize on connections - it might lead to cases where
we might go slightly over the ipc.max.pool.size() but the additional connections would timeout
after maxIdleTime - underlying PoolMap connections object is thread safe.

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