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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7291) Persist in-memory replicas with appropriate unbuffered copy API on POSIX and Windows
Date Tue, 28 Oct 2014 21:04:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7291?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14187457#comment-14187457

Chris Nauroth commented on HDFS-7291:

I cannot repro the test failures locally.  I suspect what happened is that another pre-commit
build came in and rebuilt hadoop-common-3.0.0-SNAPSHOT.jar, using the current trunk code that
still calls the native function on Linux.  I've seen some evidence of this on other builds.

I'll commit this.

> Persist in-memory replicas with appropriate unbuffered copy API on POSIX and Windows
> ------------------------------------------------------------------------------------
>                 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-7291.2.patch, HDFS-7291.3.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+. 
> As pointed by Haowei in the discussion below, FileChannel#transferTo already has support
for native unbuffered IO on POSIX platform. On Windows, JDK 6/7/8 has not implemented native
unbuffered IO yet. We change to use FileChannel#transfer for POSIX and our own native wrapper
of CopyFileEx on Windows for unbuffered copy.  

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