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Hadoop, mail # user - What's the diff btw setOutputKeyComparatorClass and setOutputValueGroupingComparator?


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What's the diff btw setOutputKeyComparatorClass and setOutputValueGroupingComparator?
Alexander Pivovarov 2011-11-27, 05:13
I tried to use one or another for secondary sort -- both options work fine
-- I get combined sorted result in reduce() iterator

Also I noticed that if I set both of them at the same time
then KeyComparatorClass.compare(O1, O2) never called,  hadoop calls
only ValueGroupingComparator.compare()

I run my tests on single node instillation.

Please help me understand the diff btw these two comparators.