Top MongoDB Interview Questions

Top MongoDB Interview Questions

Top companies like Uber, MTV, IBM, eBay, and Craigslist are turning to document data management systems, most popularly MongoDB. Unlike traditional relational database systems that use tables, rows, and columns to store data, MongoDB is document-based. It stores data in JSON-like documents which gives users the flexibility of working with unstructured text data. As MongoDB is also a NoSQL database, it is highly scalable and offers excellent performance compared to its RDBMS counterparts.

Why is it important to learn MongoDB?

It is a given the demand for MongoDB skills will rise. Enrolling in a MongoDB online course and acquiring a certification will certainly give a professional a competitive edge in the market. Considering that there is currently a high adoption rate for the cloud and big data technologies, and the fact that 60% of databases in the world are transactional, interest in MongoDB will continue to grow. This should be the main reason why it is important to learn MongoDB.

Relational database management systems (RDBMS), although they had been used for quite a while, had limitations. They could not handle unstructured and semi-structured data. Secondly, RDBMS was not designed to handle the huge volumes of data generated until only recently it added more memory to the systems making it scalable vertically. Still, storage and analytics of large data volumes in RDBMS turned out to be quite expensive.

Additionally, for most businesses data is transactional in nature and a management system that can perform real-time analytics for huge fast-evolving data sets will certainly boost productivity. Secondly, because cloud computing is the new normal for business operations, MongoDB has proved to be the go-to database management system because it has the capacity to handle big data and its SaaS Atlas version is available in the cloud.

Top MongoDB interview questions

After learning MongoDB, you will be out in the field looking for an opportunity to put your knowledge into practice. The job market, despite high demand for the skill, is usually competitive because recruiters will settle for nothing but the best talent.

Should you prepare for an interview?

Yes and thoroughly at that. Here are questions you should expect from an interviewing panel if you are seeking an opportunity in a MongoDB related role.

#1 What are the limitations of RDBMS?

RDBMS, referring to the relational database management system, is a data management system used to store data in the form of tables, i.e rows, and columns. The limitations of RDBMS include

  • Lack of capacity to handle complex unstructured data including images, audios, videos, emails, social media, and text as well as huge data volumes
  • Only stores data in tables with relational values
  • It is difficult to recover lost data
  • High set-up and maintenance cost

#2 What are NoSQL databases?

NoSQL databases are non-relational database management systems that allow for storage and retrieval of data in other means apart from the tabular relations.

#3 Name the types of NoSQL databases

There are four types including:

  • Graph-based NoSQL database
  • Document-based NoSQL database
  • Key-value NoSQL database
  • Column-based NoSQL database

#4 What type of NoSQL database is MongoDB?

MongoDB is a document-based NoSQL database that stores data in the form of JSON-like documents.

#5 Which languages does MongoDB support?

MongoDB supports several programming languages including C, C#, C++, .NET, Java, Javascript, Python, PHP, Perl, Node.js, Scala, Ruby, Haskell, Erlang, and Go.

#6 What are the important features of MongoDB?

  • Highly scalable
  • High performance
  • Document-based
  • Faster than traditional databases
  • Rich query language

#7 What is a Namespace in MongoDB?

A Namespace is a concatenation of the database name and collection name. For instance school teachers in which school is the database name and teachers the collection name.

#8 What is a replica set in MongoDB?

A replica set is a group of mongo instances that host the same dataset. A replica set forms the basis of all production deployments by providing redundancy and increasing data availability through replication of data on various database servers.

#9 Define primary and secondary replica sets

In a replica set, there are two nodes. The primary node whose function is to accept write operations and the secondary node which is a read-only node that replicates data from the primary node.

#10 How does replication work in MongoDB?

The process of synchronizing data across different database servers is known as replication. In a replica set, one node is primary and the other secondary. The primary node accepts writes while the secondary node replicates data in multiple database servers. When a single server is lost, data is not lost as it will still be available on other servers.

#11 Why is MongoDB better than other SQL databases?

MongoDB is a highly flexible and scalable database that supports a range of document structures. Secondly, it is faster than SQL databases thanks to efficient indexing and storage.

#12 Does MongoDB support foreign key constraints?

No. MongoDB does not support foreign key relationships.

#13 How is a primary key-foreign key relationship achieved in MongoDB?

A primary key-foreign relationship can be achieved by embedding a document inside another document within a single structure.

#14 What is the function of journaling in MongoDB?

Journaling is used to create backups so that in the event the server crashes, the journal is used to replay writes that have not yet been written on data files.

#15 What happens when an index is too large to fit into RAM?

When an index can’t fit in the RAM, MongoDB automatically reads the index. Compared to reading the RAM, reading the index is faster.

#16 If you remove an object attribute, is it deleted from the database?

Yes, it is deleted. This is the reason why it would be better eliminating the attribute and then saving the object once more.

#17 What are indexes in MongoDB?

Indexes are special data structures that store specific fields and then sort these fields in order of their value. Indexes make it possible to execute query-matching and range-based query operations efficiently.  Without indexes, MongoDB has to perform a collection scan, in other words, scan the entire document collection which takes a lot of time.

#18 What is a covered query in MongoDB?

In a covered query:

  • All the fields used in the query are part of an index used in the query
  • The fields returned in the results are in the same index

#19 Explain GridFS in MongoDB

GridFS is a structure used to store and retrieve files that are larger than the specified BSON-document size limit of 16mb. GridFS divides a large file into chunks and stores each chunk separately for easy retrieval. Two files are used by default fs.files for metadata and fs.chunks for the chunks.

#20 At what interval does MongoDB write updates to the disk?

Updates are written to the disk every 60 seconds by default. This can be configured with the commitIntervalMs and syncPeriodSecs options.

#21 How do you achieve transaction and locking in MongoDB?

Transaction and locking can be achieved through nesting or embedding of documents.

#22 What is Aggregation in MongoDB?

An Aggregation is an operation used to process the data that returns computed results. Aggregation groups the values from different documents together and then performs operations in the grouped data to yield a single result.

#23 What are the three ways of Aggregation in MongoDB?

  • Aggregation pipeline
  • The map-reduce function
  • Single-purpose aggregation

#24 What is Sharding in MongoDB

Sharding is the process through which data is stored across multiple machines. This is MongoDB’s way of meeting deployments with very large data sets and writing throughput demands. There are three components of a sharded cluster including shards, query routers, and config servers.

#25 What is CRUD in MongoDB?

CRUD in MongoDB refers to:

  • Create
  • Read
  • Update
  • Delete 

First, you need some training

We hope that these interview questions will be helpful as you prepare for your interview. However, the first step into this journey is getting a clear understanding of the concepts and techniques of MongoDB. To do this, consider enrolling for a MongoDB course to equip yourself not only with the knowledge required to ace the interview but also the skills needed to be competent afterward. In addition, it will help to polish your HTML, CSS, and JavaScript knowledge if you haven’t already done so.

Raj Hirvate
Hi, I'm Raj Hirvate and I am a Tech Blogger from India. I like to post about technology and product reviews to the readers of my blog. Apart from blogging i'm a big Anime fan I Love Watching Naruto, One piece and Death Note.

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