Steve Loughran created HADOOP-13985:
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             Summary: 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


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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