[
https://issues.apache.org/jira/browse/MAPREDUCE-3310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13749844#comment-13749844
]
Harsh J commented on MAPREDUCE-3310:
------------------------------------
Relevant discussion: http://search-hadoop.com/m/jq7f6Yds8T1
> Custom grouping comparator cannot be set for Combiners
> ------------------------------------------------------
>
> Key: MAPREDUCE-3310
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-3310
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: client
> Affects Versions: 0.20.1
> Environment: All
> Reporter: Mathias Herberts
>
> Combiners are often described as 'Reducers running on the Map side'.
> As Reducers, Combiners are fed <K,{V}>, where {V} is built by grouping values
> associated with the 'same' key.
> For Reducers, the comparator used for grouping values can be set
> independently of that used to sort the keys (using
> Job.setGroupingComparatorClass).
> Such a configuration is not possible for Combiners, meaning some things done
> in Reducers cannot be done in Combiners (such as secondary sort).
> It would be handy to have a Job.setCombinerGroupingComparatorClass method
> that would allow the setting of the grouping comparator used when applying a
> Combiner.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
