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From "Xiaoyu Yao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7291) Persist in-memory replicas using unbuffered IO should only applies to supported Linux version
Date Mon, 27 Oct 2014 05:06:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14184844#comment-14184844
] 

Xiaoyu Yao commented on HDFS-7291:
----------------------------------

Thanks [~aw] and [~cnauroth] for the good suggestions. I will switch to use native uname()
call to retrieve the kernel version information. 

> Persist in-memory replicas using unbuffered IO should only applies to supported Linux
version
> ---------------------------------------------------------------------------------------------
>
>                 Key: HDFS-7291
>                 URL: https://issues.apache.org/jira/browse/HDFS-7291
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode
>    Affects Versions: 2.6.0
>            Reporter: Xiaoyu Yao
>            Assignee: Xiaoyu Yao
>         Attachments: HDFS-7291.0.patch, HDFS-7291.1.patch
>
>
> HDFS-7090 changes to persist in-memory replicas using unbuffered IO on Linux and Windows.
On Linux distribution, it relies on the sendfile() API between two file descriptors to achieve
unbuffered IO copy. According to Linux document at http://man7.org/linux/man-pages/man2/sendfile.2.html,
this is only supported on Linux kernel 2.6.33+.  This JIRA is to limit the usage of sendfile()
for lazy persist only on Linux distribution with kernel version higher than 2.6.33. For unsupported
version, lazy persist will fallback to normal buffered IO.



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