Difference between combiner and partitioner

 Combiner can be viewed as mini-reducers in the map phase. They perform a local-reduce on the mapper results before they are distributed further. Once the Combiner functionality is executed, it is then passed on to the Reducer for further work.

where as Partitioner come into the picture when we are working on more than one Reducer. So, the partitioner decide which reducer is responsible for a particular key. They basically take the Mapper Result(if Combiner is used then Combiner Result) and send it to the responsible Reducer based on the key

With Combiner and Partitioner scenario : 

With Partitioner only scenario :

Examples :