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Top MongoDB Interview Questions and Answers You Need to Practice

by Interview Kickstart Team in Interview Questions
October 19, 2022

Top MongoDB Interview Questions and Answers You Need to Practice

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MongoDB interview questions consist of topics, such as transactions, MongoDB charts, the concept of pipeline, and many others. You must have an in-depth knowledge of MongoDB and how it works. MongoDB is an open-source NoSQL database written in C++ language. It works on the concepts of document and collection. 

MongoDB has gained immense popularity among tech companies due to its flexibility and easy usage. You must prepare the following MongoDB interview questions to ace your tech interview prep for companies that need MongoDB expertise. Read on to discover the vital concepts that form an integral part of MongoDB interview questions, including sharding, replication, slicing, and much more. 

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If you wish to brush up on MongoDB basics and advanced concepts, go through the following most anticipated MongoDB interview questions.

Here's what we'll cover:

  • Most Asked MongoDB Interview Questions and Answers
  • MongoDB Interview Questions for Experienced Developers
  • Some Additional MongoDB Interview Questions for Practice
  • FAQs on Interview Questions on MongoDB

Most Asked MongoDB Interview Questions and Answers

Here are some popular MongoDB interview questions and answers that cover the vital concepts for software engineer interviews.

Q1. What is MongoDB? Why is it gaining popularity? 

MongoDB is a document database that helps build scalable and highly available web applications with high performance. It is a document-oriented DBMS. 

Presently, the internet has ample big data and complexities, and a NoSQL database addresses all these problems. NoSQL database can handle and sort all types of unstructured and complicated data.

Q2. Which languages are compatible with MongoDB?

MongoDB offers official driver support for Java, C, C++, C#, Node.js, PHP, Perl, Python, Ruby, Go, Scala, and Erlang.

Q3. How is MongoDB better than other SQL databases? 

MongoDB emerges as a better option than other SQL databases due to its highly flexible and scalable document structure.

  • It is faster than SQL databases due to efficient storage techniques and indexing. 
  • Document oriented
  • Rich query language
  • High performance
  • Highly available
  • Easily scalable

Q4. How is MongoDB different from Cassandra?

The interviewer can put up comparative MongoDB interview questions to gauge the vastness of your knowledge. The following table enumerates the key difference between MongoDB and Cassandra:



MongoDB is a cross-platform document-oriented database system.

Cassandra is a high-performance distributed database system.

MongoDB is written in C++.

It is written in Java.

MongoDB is easy to administer in the case of failure.

Cassandra provides high availability with no single point of failure.

Q5. How is MongoDB different from CouchDB?

You must consider the following points of difference while answering such MongoDB interview questions: 



MongoDB is faster than CouchDB.

It is comparatively slower. 

It is less safe.

It is safer than MongoDB.

Triggers are not available.

Triggers are available. 

MongoDB serializes JSON data to BSON.

CouchDB doesn't store data in JSON format.

Q6. How is MongoDB different from the Redis database?

This is one of the frequently asked MongoDB interview questions that require you to draw comparisons between the two services. The differences between MongoDB and Redis are as follows:

  • Redis is faster than MongoDB.
  • MongoDB has document type storage while Redis has key-value storage.
  • MongoDB is easier to code than Redis.  

Q7. How can you achieve primary key - foreign key relationships? 

You can achieve primary key - foreign key relationships in MongoDB by embedding a document inside another. For instance, you can embed an address document inside a customer document.

Q8. What are collections in MongoDB?

MongoDB does not have tables. Instead, it uses "Collections" to store data. Collections in MongoDB are groups of MongoDB documents that can have different fields. It exists within a single database. 

Q9. What is a namespace in MongoDB?

A namespace in MongoDB is a concatenation of the database name and the collection name or index. Every document in MongoDB belongs to a namespace. 

Q10. Explain the structure of ObjectID in MongoDB?

ObjectID in MongoDB is a 12-byte BSON type. You can describe the structure as follows:

  • The first 4 bytes value represents the time in seconds
  • The next 3 bytes represent the machine identifier
  • 2-byte process id
  • The last 3 bytes represent the counter

MongoDB Interview Questions for Experienced Developers

You must be prepared for a combination of these MongoDB interview questions. The exact questions may vary depending on the job type, but they will focus on the following key concepts. 

Q1. What is sharding in MongoDB? 

Sharding in MongoDB refers to a procedure of storing data records across multiple machines. This MongoDB approach helps meet the demands of data growth. It draws a horizontal partition of data in a database or search engine, and every partition is a shard or database shard.

Q2. How does MongoDB ensure that the shard chunks are uniformly distributed?

MongoDB uses the hashed shard key functionality to ensure that the shard chunks are evenly distributed. If you do not use the hashed field in your queries, you could actually hurt performance because then a non-targeted scatter/gather query has to be used.

Q3. What is a slice in MongoDB? How would you slice?

Slicing is one of the key concepts that interviewers focus on in MongoDB interview questions. The $slice operator in MongoDB decides the retrieval of a number of items of an array that a query returns. It accepts a number (can also be a negative number) as an argument and returns the output.

When positive, $slice returns up to the first n elements in the array. If you specify the <position>, $slice returns the first n elements that start from the position. When negative, $slice returns up to the last n array elements. However, n cannot resolve to a negative number if you specify the <position>. 

Q4. What is replication? What is a replica set?

In MongoDB, replication is the process by which a copy of the same data set is created in more than one MongoDB server. You can use a replica set to carry out replication.

A group of MongoDB instances that host the same data set constitute a replica set.

A replica set has a primary node and other secondary nodes. Generally, it requires a minimum of three nodes. All data replication takes place from the primary to secondary nodes.

Q5. What are primary and secondary nodes in MongoDB?

The primary nodes, also called master nodes in MongoDB, can accept writes. The replication in MongoDB is a single master, i.e., only one node can accept write operations at a time. 

All nodes other than the primary nodes in a replica set are secondary nodes or slave nodes. These are read-only nodes. They replicate from the primary member.

Q6. What are Indexes in MongoDB?

Indexes in MongoDB help execute queries efficiently. In the absence of indexes, MongoDB will have to scan every document in a collection to choose documents that match the query statement. 

So, when an appropriate index is present, MongoDB can use the index to limit the number of documents it needs to scan. For example, the_id collection index is created for every collection by MongoDB.

Q7. What is the MongoDB index key limit?

A MongoDB collection can have a maximum of 64 indexes. The index name can have a length of a maximum of 125 characters. A compound index cannot have more than 31 fields indexed.

Q8. What is the significance of profiler in MongoDB?

The profiler in MongoDB collects information about Database Commands executed against a running MongoDB instance. You can find queries and write operations using a profiler. You can enable profiling on a per-instance or a per-database basis. A database profiler writes all the collected data to the capped collection- system.profile.

Q9. What do you understand about CRUD operations in MongoDB?

CRUD operations are the basic methods of interacting with a MongoDB server. CRUD is the abbreviation for Create, Read, Update, and Delete. The CRUD methods offer primary ways to manage the data in your databases.

Q10. Why are MongoDB data files large in size?

The file size in MongoDB is larger than the storage size because it includes index extents and yet-unused space in data files. The file size decreases when you delete a database, but it does not decrease as you remove collections, documents, or indexes.

Q11. How would you configure the cache size in MongoDB?

You cannot configure the cache size in MongoDB. MongoDB utilizes all the free spaces available on the system automatically via memory-mapped files.

Q12. How would you configure the cache size for WiredTiger in MongoDB?

You can specify the maximum size of the cache that WiredTiger would use. You should set it to a value less than the amount of RAM available in the container. You can do this by using storage.wiredTiger.engineConfig.cacheSizeGB option. 

Q13. How does MongoDB provide concurrency?

Concurrency is one of the important topics for MongoDB interview questions.MongoDB supports concurrency via reader-writer locks. MongoDB allows multiple clients to read and write the same data, although MongoDB employs locking and concurrency control to prevent users from modifying the same data simultaneously. 

Q14. What is MongoDB Atlas?

MongoDB Atlas is a multi-cloud database service that simplifies deploying and managing your databases. It offers the versatility you need to deploy, operate, scale, and build resilient and performant global applications on various cloud providers. 

Q15. What is Mongosh?

A MongoDB shell is referred to as Mongosh. It is a completely functional JavaScript and Node.js 14. x REPL environment that helps you interact with MongoDB deployments. You can use Mongosh to test queries and operations directly with your database. It is available as a standalone package in the MongoDB download center.

Some Additional MongoDB Interview Questions for Practice

Here are some additional MongoDB technical interview questions on various operations you can perform in MongoDB. You must practice these for your tech interview.

  1. What is the command to insert many documents to the collection of a MongoDB database?
  2. How would you insert a file in the MongoDB terminal?
  3. How is insert different from save in MongoDB?
  4. How will you perform CRUD operations in MongoDB using Node.js?
  5. How will you delete data in MongoDB collection using multiple conditions?
  6. How many writes per second can MongoDB handle?
  7. What are MongoDB charts?
  8. What is the aggregation framework in MongoDB?
  9. What are TTL indexes in MongoDB, and how are they used?
  10. How does the inverted index work in MongoDB?
  11. How is partitioning different from sharding?
  12. What is the use of $match, $in, $and in MongoDB?

Check out our learn and problems page to ace your coding interviews.

FAQs on Interview Questions on MongoDB

Q1. How to prepare for MongoDB interview questions?

The best way to ace MongoDB interview questions is to practice the most commonly asked questions and get a sense of what you might encounter during your interview. You should also practice mock interviews to become acquainted with the interview environment and boost your confidence. Practicing coding questions will assist you in acing the coding rounds.

Q2. Are MongoDB interview questions hard?

You can easily answer the MongoDB interview questions if you prepare the basic concepts well. MongoDB interviewees rate the interview questions as easy-medium level.

Q3. What does a MongoDB software developer do at top tech companies?

If you are a MongoDB developer, you should be adept at managing database administration, which is very crucial in providing all the vital information to the company. You must clearly understand and translate business specifications to extend effective solutions. It is essential to convey these abilities while answering the MongoDB interview questions.

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Our tried & tested strategy for cracking interviews
How FAANG hiring process works
The 4 areas you must prepare for
How you can accelerate your learnings
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