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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2866) JobConf should validate key names in well-defined namespaces and warn on misspelling
Date Thu, 21 Feb 2008 19:11:19 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12571149#action_12571149
] 

Doug Cutting commented on HADOOP-2866:
--------------------------------------

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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