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From "Hong Tang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6711) Configuration should support list of values
Date Fri, 16 Apr 2010 18:06:26 GMT

    [ 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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