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Posted to mapreduce-issues@hadoop.apache.org by "Alejandro Abdelnur (JIRA)" <ji...@apache.org> on 2013/11/15 02:18:17 UTC
[jira] [Updated] (MAPREDUCE-3310) Custom grouping comparator cannot
be set for Combiners
[ https://issues.apache.org/jira/browse/MAPREDUCE-3310?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Alejandro Abdelnur updated MAPREDUCE-3310:
------------------------------------------
Attachment: MAPREDUCE-3310-trunk.patch
> 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
> Assignee: Alejandro Abdelnur
> Attachments: MAPREDUCE-3310-trunk.patch
>
>
> 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.
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