Top 20 Hadoop Interview Questions

As predicted by Gartner that, “Big Data technology will generate 4.4 million new IT jobs at the end of the 2015 and also Hadoop will be in the most advanced analytics product by 2015”. As of now, we are in 2016, and yes the Big Data and Hadoop as well have emerged and are trending in the industries. There are a large number of jobs in the market for Hadoop and big data candidates but the candidates are not that skilled to get hired by the organisations. We have already told about the Hadoop tutorial for beginners pdf and Big data analytics courses online which a student can join to learn all the aspects of the technology. Today we are enlisting 20 Hadoop interview questions and answers. This will help you to prepare more efficiently for the Hadoop job interviews.

Hadoop Questions for Interviews

Below are the top 20 Hadoop questions for interviews that candidates can refer while preparing for the interviews

  • Hadoop Basic Interview Questions
  1. What is Big Data?

Big Data is  a huge amount of data that a traditional data processing system cannot handle and process. Big Data can be both structured as well as unstructured as it depends on the source of the data.

2. What do 3V’s of Big Data denote?

The 3V’s of big data are Variety, Volume and Velocity

a. Volume: Scale of the data

b. Velocity: It depends on the processing time of data

c. Variety : Different forms of data

3. What is Hadoop?

Hadoop is a distributed computing system that is written in Java language. It consists of some of the features like MapReduce, HDFS and Google File System

4. What platform as well as Java version is required to run the Hadoop?

The higher version or Java 1.6x are better for the Hadoop. The operating system for Hadoop is Linux and Windows. Some other operating systems famous are BSD, Mac QS/X and Solaris.

5. What kind of Hardware is best for Hadoop?

The dual processor or dual core machines that have 4-8 GB RAM using ECC memory can be used to run Hadoop efficiently. Also, it depends on the workflow needs that which one is used.

6. What commands that are used to see all  the jobs running in Hadoop cluster and kill a job in LINUX?

Hadoop job – list

Hadoop job – kill jobID

7.  What are common input formats that are defined in Hadoop?

The common input formats that are defined in Hadoop are theText Input Format, Sequence File Input Format and the last one is Key Value Input Format.

TextInputFormat is a by default input format.

8. What is InputSplit in Hadoop?

When a Hadoop job runs, it divides the input files into the chunks and then assigns each split to a mapper for further processing. It is known as InputSplit.

9.  How many InputSplits is made by a Hadoop Framework?

Hadoop can make 5 splits that are listed below:

  • 1 split for the 64K files
  • 2 splits for the 65MB files, and
  • 2 splits for the 127MB files

10. Why is RecordReader used in Hadoop?

InputSplit is assigned with a work but it doesn’t know how to have access . The record holder is responsible for the data loading from its source and converts it into the keys pair which is suitable for reading by Mapper. The RecordReader’s instance can be defined by Input Format.

11. What is JobTracker in Hadoop?

JobTracker is a service within the Hadoop that runs MapReduce jobs on the cluster.

12. What are the functionalities of JobTracker?

The main functions of JobTracker are:

  • To accept all the jobs from the client.
  • To communicate with NameNode to determine an exact location of the data.
  • To locate the TaskTracker Nodes with available slots.
  • To submit work to chosen TaskTracker node and also monitors the progress of each of the tasks.

13. Define TaskTracker.

TaskTracker is a type of node in a cluster that accepts the tasks like MapReduce and Shuffle operations from  JobTracker.

14. What is Map/Reduce job in Hadoop?

Map/Reduce is programming paradigm that is used to allow the massive scalability across thousands of server.

MapReduce basically performs 2 tasks. In the first step, map job is to collect the set of data and converts it into another set of data and in the second step, Reduce job. It takes an output from the map as the input and them compress that data tuples into the smaller set of tuples.

15. What is Hadoop Streaming?

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

16.  What is a combiner in Hadoop?

A Combiner is a kind of  mini-reduce process that operates only on the data generated by a Mapper. When Mapper gives out the data, combiner receives it as  an input and then sends the output to the reducer.

17. Is it necessary to know java to learn Hadoop?

It may be really helpful if you know Java, but if you are nil in java, it is necessary to learn Java basics and advanced version too and also get the basic knowledge of SQL.

18. How to debug Hadoop code?

There are various methods to debug Hadoop codes but the popular methods are:

  • By using Counters.
  • By the web interface provided by Hadoop framework.

19. Is it possible to provide multiple inputs to Hadoop? Explain

Yes, It is possible to provide multiple inputs to Hadoop. The input format class provides an opportunity to insert the different many directories as an input to the Hadoop job.

20. What is the relation between job and task in Hadoop?

In Hadoop, A job is divided into multiple small parts that are  known as a task.

So these were the top 20 Hadoop interview questions for fresher as well as Hadoop interview questions for experienced. These questions will help you to gear up your basic knowledge of Hadoop. So go for the interviews with confidence. Also, we will be back with some more questions on other topics as well.

If we missed out anything, do let us know in comments we will reply to you at the earliest.


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