[jira] [Commented] (HADOOP-15361) RawLocalFileSystem should use Java nio framework for rename

["Steve Loughran (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-15361?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16915908#comment-16915908 ] 

Steve Loughran commented on HADOOP-15361:
-----------------------------------------

[~boky01] -stick this up as a PR to see what Yetus says, then we can review and see how the object stores handle the new test. thanks

> RawLocalFileSystem should use Java nio framework for rename
> -----------------------------------------------------------
>
>                 Key: HADOOP-15361
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15361
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Andras Bokor
>            Assignee: Andras Bokor
>            Priority: Major
>              Labels: incompatibleChange
>         Attachments: HADOOP-15361.01.patch, HADOOP-15361.02.patch, HADOOP-15361.03.patch, HADOOP-15361.04.patch
>
>
> Currently RawLocalFileSystem uses a fallback logic for cross-volume renames. The fallback logic is a copy-on-fail logic so when rename fails it copies the source then delete it.
>  An additional fallback logic was needed for Windows to provide POSIX rename behavior.
> Due to the fallback logic RawLocalFileSystem does not pass the contract tests (HADOOP-13082).
> With using Java nio framework both could be eliminated since it is not platform dependent and provides cross-volume rename.
> In addition the fallback logic for Windows is not correct since Java io overrides the destination only if the source is also a directory but handleEmptyDstDirectoryOnWindows method checks only the destination. That means rename allows to override a directory with a file on Windows but not on Unix.
> File#renameTo and Files#move are not 100% compatible:
>  If the source is a directory and the destination is an empty directory File#renameTo overrides the source but Files#move is does not. We have to use {{StandardCopyOption.REPLACE_EXISTING}} but it overrides the destination even if the source or the destination is a file. So to make them compatible we have to check that the either the source or the destination is a directory before we add the copy option.
> I think the correct strategy is
>  * Where the contract test passed so far it should pass after this
>  * Where the contract test failed because of Java specific think and not because of the fallback logic we should keep the original behavior.



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