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Alejandro Abdelnur reassigned MAPREDUCE-3310: --------------------------------------------- Assignee: Alejandro Abdelnur > 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 > > 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 was sent by Atlassian JIRA (v6.1#6144)