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https://issues.apache.org/jira/browse/HADOOP-6711?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12857913#action_12857913
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Hong Tang commented on HADOOP-6711:
-----------------------------------
A word of caution: the proposed implementation using string concatenation is
inefficient when a user wants to add a lot of items on the list. I have been
hit by this before when using FileInputFormat.addInputPath.
> Configuration should support list of values
> -------------------------------------------
>
> Key: HADOOP-6711
> URL: https://issues.apache.org/jira/browse/HADOOP-6711
> Project: Hadoop Common
> Issue Type: New Feature
> Components: conf
> Reporter: Amar Kamat
>
> Configuration supports 2 operations namely _set()_ and _get()_. It would be
> nice to have an inbuild support for lists where there can be multiple values
> (i.e list of values) assigned to one key. A workaround could be
> {code}
> // Assume Key be the parameter key and newValue be the value to be
> added/appended
> Configuration c = new Configuration();
> String value = c.get(Key);
> value = value + " " + newValue
> c.set(Key, value);
> {code}
> One common usecase is that in a production enviroment, some user facing
> params (e.g mapred.child.java.opts) are set to default values (say for
> performance reasons). Users themselves might want to *add* to this list.
> Doing a set would overwrite the previous values. The above mentioned hack is
> doable via code but not via command line. Hence we need the framework to
> support lists.
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