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https://issues.apache.org/jira/browse/HDFS-5276?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13782443#comment-13782443
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Haohui Mai commented on HDFS-5276:
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And I'm still trying to understand the rational of addressing architectural
problems in DFSClient.
Controlling issues such as cache alignments, synchronization from JVM are also
essential to avoid contentions. Since the information is simply unavailable to
Java programs, in my personal opinions the problem might be better addressed in
the JVM, or even lower abstraction levels.
> 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
> Attachments: DisableFSReadWriteBytesStat.patch,
> HDFSStatisticTest.java, hdfs-test.PNG, jstack-trace.PNG
>
>
> 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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