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What do you mean by map-side join and reduce-side join in MapReduce?

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What do you mean by map-side join and reduce-side join in MapReduce?

Map-side join

Reduce-side join

The mapper performs the join

Each input data must be divided into the same number of partitions

Input to each map is in the form of a structured partition and is in sorted order

The reducer performs the join

Easier to implement than the map side join, as the sorting and shuffling phase sends the value with identical keys to the same reducer

No need to have the dataset in a structured form (or partitioned)

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