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https://issues.apache.org/jira/browse/HADOOP-2866?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12570967#action_12570967
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Joydeep Sen Sarma commented on HADOOP-2866:
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+1. But ..:
the mechanism proposed here - by itself - will not prevent regressions. we can
create a 'registry' of legal options - but that will not prevent a software
change that adds a new option, moves semantics of old option to the new option
- and then merrily leaves the old option behind in the registry.
(exactly what happened here. the tree has good looking code with references to
deprecated options).
we would need isolated regression tests against each registered option (tall
order indeed) for this to suffice.
besides - even the Java interfaces were obsoleted or their semantics changed
without removing old interfaces. and that's not a 'lack of mechanism' issue -
it's a pure software engineering issue.
> 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
> Fix For: 0.16.1, 0.17.0
>
> 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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