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https://issues.apache.org/jira/browse/HADOOP-3164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12591902#action_12591902
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Hadoop QA commented on HADOOP-3164:
-----------------------------------

+1 overall.  Here are the results of testing the latest attachment 
http://issues.apache.org/jira/secure/attachment/12380800/HADOOP-3164.patch
against trunk revision 645773.

    @author +1.  The patch does not contain any @author tags.

    tests included +1.  The patch appears to include 3 new or modified tests.

    javadoc +1.  The javadoc tool did not generate any warning messages.

    javac +1.  The applied patch does not generate any new javac compiler 
warnings.

    release audit +1.  The applied patch does not generate any new release 
audit warnings.

    findbugs +1.  The patch does not introduce any new Findbugs warnings.

    core tests +1.  The patch passed core unit tests.

    contrib tests +1.  The patch passed contrib unit tests.

Test results: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/2314/testReport/
Findbugs warnings: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/2314/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/2314/artifact/trunk/build/test/checkstyle-errors.html
Console output: 
http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/2314/console

This message is automatically generated.

> Use FileChannel.transferTo() when data is read from DataNode.
> -------------------------------------------------------------
>
>                 Key: HADOOP-3164
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3164
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Raghu Angadi
>            Assignee: Raghu Angadi
>             Fix For: 0.18.0
>
>         Attachments: HADOOP-3164.patch, HADOOP-3164.patch, HADOOP-3164.patch, 
> HADOOP-3164.patch, HADOOP-3164.patch, HADOOP-3164.patch
>
>
> HADOOP-2312 talks about using FileChannel's 
> [{{transferTo()}}|http://java.sun.com/javase/6/docs/api/java/nio/channels/FileChannel.html#transferTo(long,%20long,%20java.nio.channels.WritableByteChannel)]
>  and 
> [{{transferFrom()}}|http://java.sun.com/javase/6/docs/api/java/nio/channels/FileChannel.html#transferFrom(java.nio.channels.ReadableByteChannel,%20long,%20long)]
>  in DataNode. 
> At the time DataNode neither used NIO sockets nor wrote large chunks of 
> contiguous block data to socket. Hadoop 0.17 does both when data is seved to 
> clients (and other datanodes). I am planning to try using transferTo() in the 
> trunk. This might reduce DataNode's cpu by another 50% or more.
> Once HADOOP-1702 is committed, we can look into using transferFrom().

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