Hadoop Interview Questions | Eklavya Online

Hadoop Interview Questions

What is “map” and what is “reducer” in Hadoop?

Map: In Hadoop, a map is a phase in HDFS query solving. A map reads data from an input location and outputs a key-value pair according to the input type. Reducer: In Hadoop, a reducer collects the output generated by the mapper, processes it, and creates a final output of its own.

How JobTracker assign tasks to the TaskTracker?

The TaskTracker periodically sends heartbeat messages to the JobTracker to assure that it is alive. This messages also inform the JobTracker about the number of available slots. This return message updates JobTracker to know about where to schedule task.

What is distributed cache in Hadoop?

Distributed cache is a facility provided by MapReduce Framework. It is provided to cache files (text, archives etc.) at the time of execution of the job. The Framework copies the necessary files to the slave node before the execution of any task at that node.