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From "Chris Nauroth (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 17:42:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14185483#comment-14185483
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Chris Nauroth commented on HDFS-7291:
-------------------------------------

bq. My suggestion is to use FileChannel#transferTo for POSIX platforms, and have a native
code path for Windows.

Xiaoyu and I discussed the same plan offline earlier, and I'm also +1 for this approach. 
Thanks, everyone.

> 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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