Hadoop Interview Questions and Answers Set 2

11. What is commodity hardware?


12. Explain what is heartbeat in HDFS?


13. What happens when a datanode fails ?

When a datanode fails

Jobtracker and namenode detect the failure

On the failed node all tasks are re-scheduled

Namenode replicates the users data to another node

14. Explain what happens in textinformat ?



15. Explain what is sqoop in Hadoop ?


16. Mention what are the data components used by Hadoop?

Data components used by Hadoop are



17. What is rack awareness?


18. Explain how do ‘map’ and ‘reduce’ works.

Namenode takes the input and divide it into parts and assign them to data nodes. These datanodes process the tasks assigned to them and make a key-value pair and returns the intermediate output to the Reducer. The reducer collects this key value pairs of all the datanodes and combines them and generates the final output.

19. What is a Combiner?


20. Consider case scenario: In M/R system, – HDFS block size is 64 MB.

– Input format is FileInputFormat

– We have 3 files of size 64K, 65Mb and 127Mb

How many input splits will be made by Hadoop framework?

Hadoop will make 5 splits as follows −

– 1 split for 64K files

– 2 splits for 65MB files

– 2 splits for 127MB files