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https://issues.apache.org/jira/browse/HADOOP-3164?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12590837#action_12590837
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spullara edited comment on HADOOP-3164 at 4/20/08 8:36 PM:
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I tried enabling this on Mac OS X 10.5.2 (added a comparison for Mac OS X).
Throughput dropped by 8x and CPU only dropped by 2x. My test was just cat'ing
a 13G file out of a DataNode with 2 disks:
hadoop -fs cat wikipedia.xml > /dev/null
Without the patch I can get around 110-120MB/s (about the average speed of the
two disks) while with the patch enabled I get around 16MB/s.
was (Author: spullara):
I tried enabling this on Mac OS X 10.5.2. Throughput dropped by 8x and CPU
only dropped by 2x. My test was just cat'ing a 13G file out of a DataNode with
2 disks:
hadoop -fs cat wikipedia.xml > /dev/null
Without the patch I can get around 110-120MB/s (about the average speed of the
two disks) while with the patch enabled I get around 16MB/s.
> 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-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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