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From "Sreekanth Ramakrishnan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6105) Provide a way to automatically handle backward compatibility of deprecated keys
Date Wed, 02 Sep 2009 11:12:33 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6105?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12750391#action_12750391
] 

Sreekanth Ramakrishnan commented on HADOOP-6105:
------------------------------------------------

Took a look at the patch following are the comments which I had on the same:
* {{org.apache.hadoop.conf.Configuration.addDeprecation(String, String[])}} should be made
public so classes can access it.
* We dont need to call {{Class.newInstance()}} as we assume that child classes would have
static block which would add deprecated keys, so during class loading we will take care of
it.
* We should make the process deprecation and data structures all multi-threaded.
* Finally, we should handle the cases where one or all of the keys which are defined in extra.conf
are not present in class path. I would suggest suppressing exception and logging it in debug
mode.
* lastly move the loaded deprecation boolean as last line in process deprecation.

We should also take care that deprecated keys are not going to be reloaded and reprocessed
with {{Configuration.reload()}} method.

* Define the key in core-default.xml and make the same final.

> 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
>            Assignee: V.V.Chaitanya Krishna
>         Attachments: HADOOP-6105-1.patch, HADOOP-6105-2.patch, HADOOP-6105-3.patch, HADOOP-6105-4.patch,
HADOOP-6105-5.patch, HADOOP-6105-6.patch, HADOOP-6105.patch, HADOOP-6105.patch
>
>
> 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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