Thanks Edward. > Is there a way we use it for several mappers as well?
> No. That is the exact opposite goal of the combiner. It runs locally. OK, lets say a stupid scenario, when for instance one mapper is late to produce the results and it cause a waiting for a reducer task. Then, how to optimize this case? > >it may or may not run on a particular map attempt > It only runs when certain thresholds in the framework are reached. > > http://philippeadjiman.com/blog/2010/01/14/hadoop-tutorial-series-issue-4-to-use-or-not-to-use-a-combiner/ > What are these thresholds that may or may not run on a particular map attempt?
