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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-15606) FSDataInputStream/FSInputStream to implement getFileLength()
Date Mon, 05 Nov 2018 13:08:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16675115#comment-16675115
] 

Steve Loughran commented on HADOOP-15606:
-----------------------------------------

* RawLocalFS can do this with {{FileInputStream.getFileChannel.getSize()}}
* HDFS methods can be relayed to
* unencrypted S3AInputStream can just return the content length the file was created with.
If the file changes during the read (or existing changes become manifest), this will become
inconsistent
* CSE-S3 files will have to return their length differently, but I'm not sure how well seeking
works in their world anyway

> FSDataInputStream/FSInputStream to implement getFileLength()
> ------------------------------------------------------------
>
>                 Key: HADOOP-15606
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15606
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs, fs/s3
>    Affects Versions: 3.1.0
>            Reporter: Steve Loughran
>            Priority: Major
>
> server-side transcoding, predicate-pushdown filtering in storage, client-side decryption
can all result in an input stream shorter or longer than the file size as measured in getFileStatus/listFiles/listStatus.

> Assuming the length is known once open() returns, the FSDataInputStream can return the
length of the data, which can then be used for accurate seeks within the data.
> * requires the streams to know their length; easy to check (hasCapabilities), or make
the new method return an Optional<Long>, but caller will need to (a) look for this if
present and (b) fall back.
> * Could be rolled out for all our own clients/connectors, would take time for others



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