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https://issues.apache.org/jira/browse/HADOOP-13985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15842448#comment-15842448
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Steve Loughran commented on HADOOP-13985:
-----------------------------------------

I haven't touched this yet...I'll put it in

w.r.t java 8, I've only been using it in tests, but some of the streams stuff 
are really calling out to me in the s3a committer; too much time in scala has 
got me used to its APIs. And I'd like to use Optional<> over null. 

> s3guard: add a version marker to every table
> --------------------------------------------
>
>                 Key: HADOOP-13985
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13985
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: HADOOP-13345
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>         Attachments: HADOOP-13985-HADOOP-13345-001.patch, 
> HADOOP-13985-HADOOP-13345-002.patch
>
>
> This is something else we need before any preview: a way to identify a table 
> version, so that if future versions change the table structure:
> * older clients can recognise that it's a newer format, and fail
> * the future version can identify that it's an older format, and fail until 
> some fsck-upgrade operation has taken place
> I think something like a row on a path which is impossible in a real 
> filesystem, such as "../VERSION" would allow a version marker to go in; the 
> length field could be abused for the version number.
> This field would be something that'd be checked in init(), so be the simple 
> test for table existence we need for faster init



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