Mastering Hadoop 3

Map side join (replicated join)

If any of the data is small enough to fit into the main memory, then a map side join can be a good choice. In a map side join, the small dataset is loaded into the memory map during the setup phase of mapper. Large datasets will be read as input to the mapper so that each record gets joined with a small dataset and output is then emitted to a file. There is no reduce phase and therefore there will be no shuffling and sorting phases. Map side join is widely used for left outer join and inner join use cases. Let's look into examples of how we can create a Mapper class for map side join and Driver class:

• Mapper class: The following Mapper class is a template for using map side join and you can use it and modify ...