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Alex Rivera
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When running a MapReduce job with a specified combiner, is the combiner run during the sort phase? I understand that the combiner is run on mapper output for each spill, but it seems like it would also be beneficial to run during intermediate steps when merge sorting. I'm assuming here that in some stages of the sort, mapper output for some equivalent keys is held in memory at some point. If this doesn't currently happen, is there a particular reason, or just something which hasn't been implemented? Thanks in advance!
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