Top 15 MapReduce Interview Questions and Answers [For Beginners & Experienced]

Do you have an upcoming big data interview? Are you wondering what questions you’ll face regarding MapReduce in the interview? Don’t worry, we have prepared a list of the most common MapReduce interview questions asked by recruiters to help you out.

These questions range from the basics to advanced concepts of MapReduce.Additionally, We’ll cover all the frequently asked questions in this blog post about Hadoop interview questions and answers, along with the best answers, to help you crack the interview.

What is MapReduce Architecture?

A programming methodology and software framework called MapReduce Architecture is used for processing huge amounts of data. Map and Reduce are the two phases of the MapReduce program’s operation. While Reduce jobs reduce and shuffle the data, Map requests organise by separating and mapping the data.

Running MapReduce programs written in C, Python, Ruby, and Java is possible using the Hadoop MapReduce Architecture. Cloud computing MapReduce projects are equivalent, enabling a wide range of data analysis tasks to be carried out using diverse cluster computers.

Here is the MapReduce example to understand it better:

The microblogging website Twitter receives close to 500 million tweets every day, or 3000 tweets per second. With the help of MapReduce, we can view the example on Twitter. Twitter data is the input in the aforementioned MapReduce example, while MapReduce handles the tokenization, filtering, counting, and aggregating of counters.

15 Most Common MapReduce Interview Questions & Answers

1. What is MapReduce?

Hadoop MapReduce is a framework used to process large data sets (big data) across a Hadoop cluster.

2. Mention three benefits/advantages of MapReduce.

The three significant benefits of MapReduce are:

  • Highly scalable: Stores and distributes enormous data sets across thousands of servers.
  • Cost-effective: Allows data storage and processing at affordable prices.
  • Secure: It allows only approved users to operate on the data and incorporates HDFS and HBase security.

Read: MapReduce Architecture 

3. What are the main components of MapReduce?

The three main components of MapReduce are:

  • Main Driver Class: The Main Driver Class provides the job configuration parameters.
  • Mapper Class: This class is used for mapping purposes.
  • Reducer Class: Reducer class divides the data into splits.

4. What are the configuration parameters required to be specified in MapReduce?

The required configuration parameters that need to be specified are:

  • The job’s input and output location in HDFS
  • The input and output format
  • The classes containing the map and reduce functions
  • The .JAR file for driver, mapper, and reducer classes.

5. Define shuffling in MapReduce.

Shuffling is the process of transferring data from Mapper to Reducer. It is part of the first phase of the framework.

6. What is meant by HDFS?

HDFS stands for Hadoop Distributed File System. It is one of the most critical components in Hadoop architecture and is responsible for data storage.

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7. What do you mean by a heartbeat in HDFS?

Heartbeat is the signal sent by the datanode to the namenode to indicate that it’s alive. It is used to detect failures and ensure that the link between the two nodes is intact.

8. Can you tell us about the distributed cache in MapReduce?

A distributed cache is a service offered by the MapReduce framework to cache files such as text, jars, etc., needed by applications.

9. What do you mean by a combiner?

Combiner is an optional class that accepts input from the Map class and passes the output key-value pairs to the Reducer class. It is used to increase the efficiency of the MapReduce program. However, the execution of the combiner is not guaranteed.

10. Is the renaming of the output file possible?

Yes, the implementation of multiple format output class makes it possible to rename the output file.

11. What is meant by JobTracker?

JobTracker is a service that is used for processing MapReduce jobs in a cluster. The JobTracker performs the following functions:

  • Accept jobs submitted by client applications
  • Communicate with NameNode to know the data location
  • Locate TaskTracker nodes that are near the data or are available
  • Submit the work to the chosen nodes
  • If a TaskTracker node notifies failure, JobTracker decides the steps be taken next.
  • It updates the status of the job after completion.

If the JobTracker fails, all running jobs are stopped.

12. Can you tell us about MapReduce Partitioner and its role?

The phase that controls the partitioning of intermediate map-reduce output keys is known as a partitioner. The process also helps to provide the input data to the reducer. The default partitioner in Hadoop is the ‘Hash’ partitioner.

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13. Can Reducers communicate with each other?

No, Reducers can’t communicate with each other as they work in isolation.

14. What do you mean by InputFormat? What are the types of InputFormat in MapReduce?

InputFormat is a feature in MapReduce that defines the input specifications for a job. The eight different types of InputFormat in MapReduce are:

  • FileInputFormat
  • TextInputFormat
  • SequenceFileInputFormat
  • SequenceFileAsTextInputFormat
  • SequenceFileAsBinaryInputFormat
  • DBInputFormat
  • NLineInputFormat
  • KeyValueTextInputFormat

Must Read: Hitchhicker’s Guide to MapReduce

15. How does MapReduce work?

MapReduce works in two phases — the map phase and the reduce phase. In the map phase, MapReduce counts the words in each document. In the reduce phase, it reduces the data and segregates them.

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Hadoop interview questions and Answers

These Hadoop MapReduce interview questions and answers may help both freshers and experienced job applicants land their dream job.

1. What is Hadoop Map Reduce?

The Hadoop MapReduce framework is used to handle massive data sets in parallel across a Hadoop cluster. Map and reduce is a two-step procedure used in data analysis.

2. How does Hadoop MapReduce operate?

During the map phase of the MapReduce algorithm, each document’s words are counted, and during the reduction phase, data is aggregated for each document over the whole collection. The incoming data is split up for analysis during the map phase by map processes executing concurrently throughout the Hadoop architecture.

3. Explain the role of MapReduce in the hadoop mapreduce example. 

A Hadoop framework called MapReduce is used to create applications that can handle enormous volumes of data on huge clusters. Another name for it is a programming architecture that enables us to process big datasets across computer clusters. This programme enables the distributed storage of data.

4. What does Hadoop’s “speculative execution” mean? 

The master node can redundantly run another instance of the identical job on another node if it looks like one node is processing a task more slowly than the others. The task that completes first will then be approved, while the second is terminated. The term “speculative execution” refers to this technique.

5. What is NameNode in Hadoop?

Hadoop keeps all of the HDFS file location information in NameNode. It is the master node that the metadata-based job tracker operates on.


In conclusion, anyone attempting to handle large amounts of data must have a solid grasp of the MapReduce architecture and how it works with Hadoop. You’ll be better prepared to handle the difficulties of working with distributed data processing systems and prove your knowledge in interviews by studying real-world examples and practising MapReduce interview questions.

We hope that you find this blog was informative and helpful for the preparation of your interview. We have tried to cover basic, intermediate, and advanced MapReduce interview questions. Feel free to ask your doubts in the comments section below. We will try to answer them to the best of our capabilities.

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What is the use of MapReduce for Big Data?

MapReduce is a model for programming which is explicitly developed to enable easier distributed and parallel processing of Big Data sets. The MapReduce model consists of a map function that performs sorting and filtering operations and a reduce function that carries out a summary operation. This computational model is widely employed for selecting and querying data which is contained in the Hadoop Distributed File System (HDFS). It is also preferred for iterative computation of huge volumes of data. MapReduce is also suitable for performing other tasks such as searching, indexing, sorting, joining, classification and term frequency- inverse document frequency.

Does Big Data need you to have programming knowledge?

Having an Information Technology (IT) background is beneficial for working on Big Data. So that means you should be comfortable and be familiar with programming languages. Understanding the programming concepts helps to better grasp the basic computational concepts of Big Data and move on to its advanced aspects. If you do not already know how to write code, you should start learning it at the earliest to become a successful Big Data professional. This is because Big Data involves statistical and numerical analysis involving massive sets of data, which is done by programming. It would help if you learned programming languages such as Python, Java, R, C++, etc.

Can you learn Data Science without knowing Python?

It is possible to learn Data Science without learning the Python programming language. There are other computer languages that you can learn, such as Perl or R. Or you can choose to work in a field of Data Science that does not require you to employ your programming skills. However, Python is extremely popular and useful for working in Data Science. And one of the major reasons for its popularity is that it is easy to understand and implement. So you can start learning Python. Avoiding Python or programming languages can drastically limit your scope in this field of Data Science.

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