Use FileChannel.transferTo() when data is read from DataNode.
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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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