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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3164) Use FileChannel.transferTo() when data is read from DataNode.
Date Mon, 21 Apr 2008 23:15:22 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12591102#action_12591102
] 

dhruba borthakur commented on HADOOP-3164:
------------------------------------------

It would be nice if we can keep code same on all platforms as much as possible. One option
would be to raise the default io.file.buffer.size to something like 64K and use FileChannel.transferTo
on all platforms.

> 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-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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