How Does Setup Method Work in Hadoop Mapper and Reducer Classes?

What Does Hadoop Mapper Setup Method Initialize Before Processing?

Learn the role of setup() method in Hadoop Mapper/Reducer for one-time resource initialization like database connections before map/reduce processing begins, optimizing task performance.

Question

What is the role of the setup method in Mapper/Reducer?

A. To handle cluster scheduling
B. To compress intermediate data
C. To finalize output after all tasks finish
D. To initialize resources before map or reduce begins

Answer

D. To initialize resources before map or reduce begins

Explanation

The setup method in both Mapper and Reducer classes serves as a lifecycle hook that executes once per task instance before any map() or reduce() calls begin, allowing initialization of shared resources like database connections, counters, or configuration data that remain available throughout processing. This ensures efficient resource management since setup() runs only once per task rather than repeatedly per record, contrasting with the per-record map/reduce methods. Developers override public void setup(Context context) to perform task-specific initialization, making it essential for establishing connections, loading lookup tables, or validating configurations before the core data processing starts.