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https://issues.apache.org/jira/browse/HDFS-4157?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13492779#comment-13492779
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Colin Patrick McCabe commented on HDFS-4157:
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Unfortunately, there's a pretty heavy overhead making a JNI call, especially
when you look up the Java function dynamically like we do. Actually, this is
one thing that libwebhdfs does better than libhdfs.
> libhdfs: hdfsTell could be implemented a smarter than it is
> -----------------------------------------------------------
>
> Key: HDFS-4157
> URL: https://issues.apache.org/jira/browse/HDFS-4157
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: libhdfs
> Affects Versions: 2.0.3-alpha
> Reporter: Colin Patrick McCabe
> Priority: Minor
>
> In libhdfs, {{hdfsTell}} currently makes an RPC to the {{DataNode}} to
> determine the position of the stream. However, we could cache this
> information easily, since libhdfs controls access to the stream. This would
> avoid the double overhead of JNI and the RPC itself.
> This would be very helpful for {{fuse_dfs}}, since that program calls
> {{hdfsTell}} before every {{write}} or {{read}} operation. This can be quite
> a lot of overhead, since writes may be as small as 4kb (depends on FUSE
> configuration, kernel version, etc.)
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