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From "Binglin Chang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5276) FileSystem.Statistics got performance issue on multi-thread read/write.
Date Sun, 13 Oct 2013 00:29:42 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13793537#comment-13793537
] 

Binglin Chang commented on HDFS-5276:
-------------------------------------

Hi [~wheat9], volatile cannot be used as atomic variables, its += operation ( incrementAndGet
) is not thread safe, unless you add lock synchronization.

> FileSystem.Statistics got performance issue on multi-thread read/write.
> -----------------------------------------------------------------------
>
>                 Key: HDFS-5276
>                 URL: https://issues.apache.org/jira/browse/HDFS-5276
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.0.4-alpha
>            Reporter: Chengxiang Li
>            Assignee: Colin Patrick McCabe
>         Attachments: DisableFSReadWriteBytesStat.patch, HDFS-5276.001.patch, HDFS-5276.002.patch,
HDFSStatisticTest.java, hdfs-test.PNG, jstack-trace.PNG, TestFileSystemStatistics.java, ThreadLocalStat.patch
>
>
> FileSystem.Statistics is a singleton variable for each FS scheme, each read/write on
HDFS would lead to a AutomicLong.getAndAdd(). AutomicLong does not perform well in multi-threads(let's
say more than 30 threads). so it may cause  serious performance issue. during our spark test
profile, 32 threads read data from HDFS, about 70% cpu time is spent on FileSystem.Statistics.incrementBytesRead().



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