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https://issues.apache.org/jira/browse/MAPREDUCE-5791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13934339#comment-13934339
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Chris Nauroth commented on MAPREDUCE-5791:
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A few comments:
# {{ShuffleHandler}}
## {{SHUFFLE_BUFFER_SIZE}} is potentially confusing, because it's reusing
{{io.file.buffer.size}}, which is already used elsewhere, and with a different
default value. I recommend making this an MR-specific property, like
{{mapreduce.shuffle.transfer.buffer.size}}, and documenting it in
mapred-default.xml.
# {{TestFadvisedFileRegion}}
## Minor nit: we put the opening { inline, not on a separate line.
## {{out}}, {{inputFile}}, {{targetFile}}, {{target}} and {{in}} all should be
closed inside a finally block to guarantee cleanup. The {{IOUtils#cleanup}}
method is helpful for this. For {{fileRegion}}, it looks like we ought to call
{{releaseExternalResources}}:
http://grepcode.com/file/repository.jboss.org/nexus/content/repositories/releases/org.jboss.netty/netty/3.2.0.CR1/org/jboss/netty/channel/DefaultFileRegion.java.
## {{testCustomShuffleTransferCornerCases}}: This can be removed if you don't
intend to add test code in here.
> Shuffle phase is slow in Windows - FadviseFileRegion::transferTo does not
> read disks efficiently
> ------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-5791
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5791
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Nikola Vujic
> Assignee: Nikola Vujic
> Attachments: MAPREDUCE-5791.patch
>
>
> transferTo method in org.apache.hadoop.mapred.FadvisedFileRegion is using
> transferTo method from a FileChannel to transfer data from a disk to socket.
> This is performing slow in Windows, slower than in Linux. The reason is that
> transferTo method for the java.nio is issuing 32K IO requests all the time.
> In Windows, these 32K transfers are not optimal and we don't get the best
> performance form the underlying IO subsystem. In order to achieve better
> performance when reading from the drives, we need to read data in bigger
> chunks, 512K for example.
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