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From "Hemanth Yamijala (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6105) Provide a way to automatically handle backward compatibility of deprecated keys
Date Thu, 25 Jun 2009 09:57:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12723987#action_12723987
] 

Hemanth Yamijala commented on HADOOP-6105:
------------------------------------------

Initial proposal is to keep it dead simple:

- Keep a static map of keys in the Configuration class that maps the deprecated key to a set
of new keys.
- get of the deprecated key will return the value of the first new key in the mapping set.
- set of the deprecated key will set the same value to all new keys in the mapping set.
- There will be a provision to define a custom message in the configuration class whenever
access is done on the deprecated keys. Otherwise, a standard message such as: "This key is
deprecated. Use this other key instead" will be printed.
- When both old and new keys are defined, the new keys will always take precedence.



> 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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