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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6735) A minor optimization to avoid pread() be blocked by read() inside the same DFSInputStream
Date Fri, 01 Aug 2014 18:55:40 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6735?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14082749#comment-14082749
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Colin Patrick McCabe commented on HDFS-6735:
--------------------------------------------

Thanks, Steve.  And thanks Stack and Liang, for bearing with me on this one :)  Looking forward
to figuring this out.

> A minor optimization to avoid pread() be blocked by read() inside the same DFSInputStream
> -----------------------------------------------------------------------------------------
>
>                 Key: HDFS-6735
>                 URL: https://issues.apache.org/jira/browse/HDFS-6735
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>    Affects Versions: 3.0.0
>            Reporter: Liang Xie
>            Assignee: Liang Xie
>         Attachments: HDFS-6735-v2.txt, HDFS-6735.txt
>
>
> In current DFSInputStream impl, there're a couple of coarser-grained locks in read/pread
path, and it has became a HBase read latency pain point so far. In HDFS-6698, i made a minor
patch against the first encourtered lock, around getFileLength, in deed, after reading code
and testing, it shows still other locks we could improve.
> In this jira, i'll make a patch against other locks, and a simple test case to show the
issue and the improved result.
> This is important for HBase application, since in current HFile read path, we issue all
read()/pread() requests in the same DFSInputStream for one HFile. (Multi streams solution
is another story i had a plan to do, but probably will take more time than i expected)



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