In the MapReduce development framework, what is the function of the InputFormat class?

Question

Options

• ACombine key-value pairs with the same key value in the result of the map phase
• BCombine the results of all map stages to get the final result
• CSort and merge the results of the map stage
• DSplit the input data into individual splits, and further split the split into <key, value> pairs, which

• A
  3% (1)
• B
  3% (1)
• C
  9% (3)
• D
  85% (28)

Explanation

InputFormat is the entry point for all data entering a MapReduce job: it performs two distinct jobs - splitting the raw input into logical splits (chunks assigned to individual mappers), and then parsing each split into <key, value> pairs that the Mapper actually receives, making D correct.

• A is wrong because combining key-value pairs with the same key is the job of the Combiner (a mini-reducer that runs locally after the map phase).
• B is wrong because combining all map results into a final output is the job of the Reducer, not InputFormat.
• C is wrong because sorting and merging map output is handled by the Shuffle and Sort phase (also called the partitioning/merge step between map and reduce).

Memory tip: Think of InputFormat as the "door and knife" - it opens the data and cuts it into pieces (splits), then slices each piece further into <key, value> morsels the Mapper can digest. Everything after that is someone else's job.

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