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https://issues.apache.org/jira/browse/HADOOP-2866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12571161#action_12571161
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Nigel Daley commented on HADOOP-2866:
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As Joydeep points out, we've also seen incompatibilities introduced by changing
the semantics of an existing property. I think we need to be better about
deprecating properties (and their accessor methods) and introducing new ones
when a semantic change is required. Effectively, semantic changes require a
new property. Enforcing this thru testing will require specific tests for each
properties current semantics (not a small effort) so I think for now this
should be added to our code review guidelines:
http://wiki.apache.org/hadoop/CodeReviewChecklist
> JobConf should validate key names in well-defined namespaces and warn on
> misspelling
> ------------------------------------------------------------------------------------
>
> Key: HADOOP-2866
> URL: https://issues.apache.org/jira/browse/HADOOP-2866
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Affects Versions: 0.16.0
> Reporter: Aaron Kimball
> Priority: Minor
> Original Estimate: 72h
> Remaining Estimate: 72h
>
> A discussion on the mailing list reveals that some configuration strings in
> the JobConf are deprecated over time and new configuration names replace them:
> e.g., "mapred.output.compression.type" is now replaced with
> "mapred.map.output.compression.type"
> Programmers who have been manually specifying the former string, however,
> receive no diagnostic output during testing to suggest that their compression
> type is being silently ignored.
> It would be desirable to notify developers of this change by printing a
> warning message when deprecated configuration names are used in a newer
> version of Hadoop. More generally, when any configuration string in the
> mapred.\*, fs.\*, dfs.\*, etc namespaces are provided by a user and are not
> recognized by Hadoop, it is desirable to print a warning, to indicate
> malformed configurations. No warnings should be printed when configuration
> keys are in user-defined namespaces (e.g., "myprogram.mytask.myvalue").
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