MongoDB requires skill and complex coding knowledge. Interviewers often ask tricky questions to test whether candidates are perfect for the job or not. So, while preparing for Interview questions, aspirants must have complete knowledge of this database. We have come up with the top 30 questions that mostly ask by interviewers. Have a look!

Table of Contents

Q1. What do you understand by MongoDB?

MongoDB is a popular database for modern applications. This document-based database is highly scalable and quite good at performance.

Q2. Why MongoDB is counted among the best?

Since it’s the NoSQL database, comes with the following features-

  • High Performance
  • Document-oriented
  • Easy scalability
  • High availability
  • Rich query language

Q3. Define the role of the profiler in MongoDB.

The profiler’s role is to show the performance & analyzing every operation characteristic. On using profilers, you will get all queries that are slower than usual. 

Q4. Compare MongoDB with CouchbaseDB and Couchbase.

Though MongoDB, CouchbaseDB, and Couchbase are similar in several aspects, yet when it comes to crossing points, model execution, duplication, storage, etc, these are different. 

Q5. When to use namespace in MongoDb?

At the time of the sequencing database names & the collection, we make use of a namespace. 

Q6. On removing object attribute. Would it be erased from MongoDB as well?

Yes, it would be deleted. Thus, it’s better to eliminate an object attribute and save it again. 

Q7. Is there any way of moving the old file to move chunks?

Yes, you can do that. Once you are done with the functions, whatever old files you have changed to backup files & then you can move these files into the directory of moveChunk during slices balancing. 

Q8. How this database provides you with consistency?

This database makes use of reader-writer locks. It means this allows users to access any supply such as databases & collections simultaneously. Plus, it also provides private access straight to single writes. 

Q9. What is the full form of CRUD?

MongoDB gives you CRUD operations and which stands for

  • C- Create
  • R- Read
  • U-Update
  • D- Delete

Q10. What do you understand by Sharding?

Storing data on multiple machines is called Sharding in MongoDB. This is done to accomplish the requirements of data growth. A horizontal partition is formed in the database & each partition is named a shard or database shard.

Q11. Which syntax in MongoDB you will use for creating a collection?

The following syntax will be used for creating a collection–

MongoDb Collection

Q12. To drop collection, what syntax you will use?

This is the syntax we use to drop collection-

Q13. Replication – What is it?

Replication is a process that helps to synchronize data across several servers. Since database servers have multiple copies of data, replication prevents the database to lose the data from a single server. This also ensures that it would recover from service interruptions and hardware failure. 

Q14. GridFS is widely used in MongoDB. Why do we use it?

GridFS basically used for retrieving and strong large files such as image, audio, and video files.

Q15. Highlight the use of Journaling.

Well, Journaling is used for the MongoDB safe backups. 

Q16. What is the difference between MySQL and MongoDB? 

No doubt, both are open-source databases and free of cost. But there are several things that separate one from another. They are different in terms of relationship, data representation, schema design & definition, normalization, performance speed, and much more. The biggest difference is – MySQL is a relational database whereas MongoDB is a non-relational database. 

Q17. MongoDB is written in which language?

MongoDB is written in C++. However, client and driver libraries are written in their own respective language. Though, some drivers make use of C extensions to enhance performance.

Q18. When you create a schema in MongoDB, what are the things that you need to consider?

There are the following things that need to be considered while creating a schema in MongoDB – 

  • Design schema as per the requirements of users
  • Do joins when it’s on write, not when it’s on read
  • If you want to use objects together, combine them into 1 document. Otherwise, separate them
  • Optimize schema for most frequent use cases
  • Do complex aggregation in the schema

Q19. Write the syntax of the skip() method.

The syntax of the skip() method is –

Q20. Why do we use the pretty() method?

This is used for showing results in a formatted way.

Q21 Why do we use the NoSQL database?

As we know, today’s internet is loaded with big users & big data which are making the whole thing complex with each passing day. NoSQL is simply the answer to all your worries. It’s not a conventional database management system. It’s quite easy to handle just because it’s not interrelated with the other databases. Moreover, it efficiently handles all types of complicated, messy, and unstructured data. MongoDB is also a NoSQL database. 

Q22. What are the Sharded cluster components?

The sharded cluster components are- Shards, Config servers, and Query routers

Q23. Which command will you use for creating a database?

We use the Database_Name command for creating a database. 

Q24. Name that command is being used to check a connection.

We use the following command to check the connection

Q25. Define primary as well as secondary replica set.

All the write operations are accepted from clients in the primary replica set whereas the secondary replica set’s oplog & applies operations to their datasets. It means primary replica sets are reflected by secondary datasets.

Q26 How you can update your documents in the collection?

Save () and update() are two methods via which we can achieve this. 

Q27. Define the Aggregation pipeline in one line. 

The aggregation pipeline is a framework that is used to perform aggregation tasks. The aggregation pipeline ultimately transforms documents into aggregated results. 

Q28. What do you understand by Horizontal and Vertical scaling?

Horizontal scaling distributes data over multiple shards or servers. It simply divides the dataset. However, vertical scaling adds more storage resources and CPU to enhance capacity. 

Q29. Which method you will use for creating an index?

createIndex() for creating an index in MongoDB.

Q30. Why do we use Dot notation?

For accessing elements of the array & embedded document field, MongoDB makes use of Dot notation. 

These are some of the most important questions that are often asked by the interviewer to test your knowledge and skills. So, the next time you are ready to go for an interview, make sure you have gone through all these questions. All the Best!