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From "Philip Zeyliger (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6105) Provide a way to automatically handle backward compatibility of deprecated keys
Date Mon, 06 Jul 2009 16:47:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12727615#action_12727615
] 

Philip Zeyliger commented on HADOOP-6105:
-----------------------------------------

Hemanth,

This JIRA is about backwards-compatibility of deprecated keys, which is something my comment
addresses, so I thought it fit in well here.  Think of it as an alternative solution to the
problem you're trying to solve by keeping the map of deprecated keys in Configuration.java.
 Keeping a deprecation map is expedient and simple, but I think it may hamper a better, longer-term
solution.

The design goals above are "out of thin air" (in the sense that they haven't been discussed
on JIRA outside of the JIRAs mentioned above and MAPREDUCE-475), though I hope they're reasonable.
 They were discussed a bit at http://wiki.apache.org/hadoop/DeveloperOffsite20090612, too.
 That said, I hope they help to frame the conversation a bit

I very very much want there to be a path to be able to rename configuration keys, but I want
to make sure that the solution that comes out of this JIRA is compatible with some future
work.

-- Philip

> Provide a way to automatically handle backward compatibility of deprecated keys
> -------------------------------------------------------------------------------
>
>                 Key: HADOOP-6105
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6105
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: conf
>            Reporter: Hemanth Yamijala
>
> There are cases when we have had to deprecate configuration keys. Use cases include,
changing the names of variables to better match intent, splitting a single parameter into
two - for maps, reduces etc.
> In such cases, we typically provide a backwards compatible option for the old keys. The
handling of such cases might typically be common enough to actually add support for it in
a generic fashion in the Configuration class. Some initial discussion around this started
in HADOOP-5919, but since the project split happened in between we decided to open this issue
to fix it in common.

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