where does combiners combine mapper outputs - in map phase or reduce phase in a Map-reduce job?

Question

I was under the impression that combiners are just like reducers that act on the local map task, That is it aggregates the results of individual Map task in order to reduce

Answer 1

1. A combiner will not run if it is a Map-Only job.

2. A combiner only runs if there are more than 3 spill files written to the disk.