Hadoop Interview Questions and Answers

Ques 26. What happens when a data node fails?

If a data node fails the job tracker and name node will detect the failure. After that, all tasks are re-scheduled on the failed node and then name node will replicate the user data to another node.

Ques 27. What is Hadoop Streaming?

Hadoop streaming is a utility which allows you to create and run map/reduce job. It is a generic API that allows programs written in any languages to be used as Hadoop mapper.

Ques 28. What is a combiner in Hadoop?

A Combiner is a mini-reduce process which operates only on data generated by a Mapper. When Mapper emits the data, combiner receives it as input and sends the output to a reducer.

Ques 29. What are the Hadoop's three configuration files?

Following are the three configuration files in Hadoop:

• core-site.xml
• mapred-site.xml
• hdfs-site.xml

Ques 30. What are the network requirements for using Hadoop?

Following are the network requirement for using Hadoop:

• Password-less SSH connection.
• Secure Shell (SSH) for launching server processes.