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https://issues.apache.org/jira/browse/HADOOP-2866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12571149#action_12571149
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Doug Cutting commented on HADOOP-2866:
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As others have stated, the preferred style should not be for programs to
directly set these, but rather to use accessor methods. Such accessor methods
should themselves be implemented with a constant to name the configuration
parameter. It would be good to add warnings to Hudson when code accesses a
parameter with a literal string, and I encourage patches which address this
issue.
However this does not address parameters specified on the command line or in
hadoop-site.xml. A registry would be required to properly check these. Global
registries are hard to maintain and I am thus reluctant to introduce a new one.
But we already have a global registry in hadoop-default.xml. Perhaps we
should emit warnings if folks set properties in hadoop-site.xml that do not
have a default value in hadoop-defaults.xml. Would that help?
> 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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