Tag Archives: JobTracker

MapReduce – Mappers and Reducers

How that data is processed with MapReduce.

PTopToBottomrocessing a large file serially from the top to the bottom could take a long time.

MapReduce is designed to be a very parallelized way of managing data, meaning that your input data is split into many pieces, and each piece is processed MapReducesimultaneously.

RealReal-world scenario.  A ledger which contains all the sales from thousands of stores around the USA, organized by date. Calculate the total sales generated by each store over the last year.  Just to start at the beginning of the ledger and, for each entry, write the store name and the amount next to it. For the next entry, if store name is already there, add the amount to that store. If not, add a new store name and that first purchase. And so on, and so on.
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