[jira] Commented: (HADOOP-6105) Provide a way to automatically handle backward compatibility of deprecated keys

["Hemanth Yamijala (JIRA)" <ji...@apache.org>]

    [ 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:
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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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