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https://issues.apache.org/jira/browse/HDFS-246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12840814#action_12840814
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Qi Liu commented on HDFS-246:
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I believe HDFS-814 is not good for general application use. DFSDataInputStream
is a concrete sub-class while FSDataInputStream is an abstract parent class.
FileSystem.open returns an instance of FSDataInputStream instead of
DFSDataInputStream. Explicitly cast FSDataInputStream to DFSDataInputStream is
simply not safe. What if in future or in some cases, FileSystem.open returns an
instance other than DFSDataInputStream? I still believe the proper way to
implement this would be adding a public method to FSDataInputStream abstract
class, and add such method to all implementations.
> Add a method to get file length for Seekable, FSDataInputStream and libhdfs
> ---------------------------------------------------------------------------
>
> Key: HDFS-246
> URL: https://issues.apache.org/jira/browse/HDFS-246
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Qi Liu
> Assignee: Qi Liu
> Fix For: 0.22.0
>
> Attachments: HADOOP-5143-2.patch, HADOOP-5143.patch, hadoop.patch
>
>
> When open any seekable file, it should be able to get the length of the file
> via Seekable interface, since the seek method should be able to detect
> seeking beyond the end of file. Such interface can benefit distributed file
> systems by saving a network round-trip of
> FileSystem.getFileStatus(Path).getLen() for any open file.
> In libhdfs, such interface should also be exposed to make native program
> taking advantage of this change.
> I have the changes locally for all FSInputStream concrete classes. The change
> can be considered trivial, since some of the FSInputStream classes already
> have a method named getFileLength(), or a member field named size/length/end.
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