[jira] Commented: (HADOOP-3164) Use FileChannel.transferTo() when data is read from DataNode.

["Raghu Angadi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12585250#action_12585250 ] 

Raghu Angadi commented on HADOOP-3164:
--------------------------------------


This essentially means we need to implement write-timeout ourselves instead of using wait implementation in SocketOutputStream. May be SocketOutputStream could support something like waitForRead().

> 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
>
> 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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