aggregate - Hadoop combiners with aggregator functions -


when using 1 of aggregator function in place of reducer, hadoop smart enough use same function combiner phase?

they fulfill partly same purpose aggregator more generic , can used in cases combiner can not.

so it's definite no, aggregator not used combiner automatically. if want used combiner have specify such.

quote cascade, "combiners limited associative , commutative functions only, 'sum' , 'max'. , in order work, values emitted map task must serialized, sorted (deserialized , compared), deserialized again , operated on"


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