[jira] [Assigned] (HDFS-6735) A minor optimization to avoid pread() be blocked by read() inside the same DFSInputStream

["Lars Hofhansl (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-6735?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Lars Hofhansl reassigned HDFS-6735:
-----------------------------------

    Assignee: Lars Hofhansl  (was: Liang Xie)

> 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: Lars Hofhansl
>         Attachments: HDFS-6735-v2.txt, HDFS-6735-v3.txt, HDFS-6735-v4.txt, HDFS-6735-v5.txt, HDFS-6735-v6.txt, HDFS-6735-v6.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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