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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8629) Add option for TableMapping to reload mapping file on match failure
Date Sat, 28 Jul 2012 00:21:34 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8629?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13424230#comment-13424230

Steve Loughran commented on HADOOP-8629:

Auto reload of the table mapping is not completely straightforward as
* need to make upload thread safe.
* reload logic needs policy on failure to reload the file. Retain the old mapping?
* reload logic needs policy on removal of entries from the file and changed values. With caching
in front of the class, these changes won't get picked up anyway, but if we strip that out
by not caching in-VM lookups, then it may become an issue. 
> Add option for TableMapping to reload mapping file on match failure
> -------------------------------------------------------------------
>                 Key: HADOOP-8629
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8629
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: util
>            Reporter: Steve Loughran
>            Priority: Minor
> As commented in HADOOP-7030, the table mapping topology mapper handles new node addition
worse than the script mapping, because the table mapping is frozen for the life of the service.
> I propose adding an option (true by default?) for the class to look at the timestamp
of the mapping file, and reload it on a change -if a hostname lookup failed. 

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