What Is The Main Difference Between Mapreduce Combiner And Reducer?

1.	What Is The Main Difference Between Mapreduce Combiner And Reducer?
Answer» Both Combiner and REDUCER are optional, but most FREQUENTLY used in MAPREDUCE. There are three main differences such as: combiner will get only ONE input from one Mapper. While Reducer will get multiple mappers from different mappers. If aggregation required used reducer, but if the function follows commutative (a.b=b.a) and associative a.(b.c)= (a.b).c law, use combiner. Input and output KEYS and values types must same in combiner, but reducer can follows any type input, any output format. Both Combiner and Reducer are optional, but most frequently used in MapReduce. There are three main differences such as:

Answer»

Both Combiner and REDUCER are optional, but most FREQUENTLY used in MAPREDUCE. There are three main differences such as:

combiner will get only ONE input from one Mapper. While Reducer will get multiple mappers from different mappers.
If aggregation required used reducer, but if the function follows commutative (a.b=b.a) and associative a.(b.c)= (a.b).c law, use combiner.
Input and output KEYS and values types must same in combiner, but reducer can follows any type input, any output format.

Both Combiner and Reducer are optional, but most frequently used in MapReduce. There are three main differences such as:

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