Hadoop combiners with aggregator functions

Question

When using one of the aggregator function in place of a reducer, will Hadoop be smart enough to use same function for combiner phase?

Answer 1

Both combiner & aggregator fulfill partly the same purpose but the aggregator is more generic and can be used in cases where the combiner can not.

So it's a definite no, the aggregator will not be used as a combiner automatically. If you want it to be used as a combiner you will have to specify it as such.

Hope it will help you to some extent.