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https://issues.apache.org/jira/browse/MAPREDUCE-3310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13873905#comment-13873905
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Jonathan Eagles commented on MAPREDUCE-3310:
--------------------------------------------
It looks like the behavior before is to default combiner group comparator to
sort output key comparator. If I route Tez's getCombinerKeyGroupingComparator()
to getSortComparator(), would this have the same functionality as
pre-MAPREDUCE-3310. This would allow Tez to compile for both hadoop-2.2.0 and
hadoop-2.4.0.
Jon
> 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
> Fix For: 1.3.0, 2.4.0
>
> Attachments: MAPREDUCE-3310-branch-1.patch,
> MAPREDUCE-3310-branch-1.patch, MAPREDUCE-3310-trunk.patch,
> MAPREDUCE-3310-trunk.patch, MAPREDUCE-3310-trunk.patch,
> 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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