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https://issues.apache.org/jira/browse/MAPREDUCE-5791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13934321#comment-13934321
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Nikola Vujic commented on MAPREDUCE-5791:
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I agree about the root cause. I saw that code too. Since I use Oracle JDK, I
wanted to verify that the native implementation does not exists in Oracle JDK,
but I couldn't find source code for nio.dll in Oracle JDK. Thus I run the test
with OpenJDK in order to compare performance and I observed the same behavior.
So, both JDKs are behaving the same in the shuffle, which means that Oracle JDK
is also missing native implementation for the zero-copy transfer on Windows
(assuming that the zero-copy transfer would work at least as fast as buffer
copy).
It is good idea to try JNI call to TransmitFile. Actually, it may happen to get
a perf boost from TransmitFile due to a shuffle phase being CPU bound now (CPU
is at 100% during shuffle with buffer copy). I will have to try it.
> 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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