Top MongoDB Interview Questions and Answers

MongoDB has consistently been ranked among the top five most popular NoSQL Database Management Systems (DMS). If you’re applying for a position involving database management, then you stand a good chance of working with MongoDB at some point.

Whether you’re upskilling or interviewing for a Database Management position working with MongoDB, it’s prudent to be familiar with the more common MongoDB questions and answers. In the latter case, it pays to prepare for that interview and not get caught unawares. But even if you’re just interested in learning about MongoDB for the purposes of upskilling, bare in mind that acquiring this kind of knowledge could very well lead you into looking for that better career, and that means you’ll end up facing an interview sooner or later. Might as well be ready!

Whatever the case, you should check these top MongoDB interview questions and answers, and be ready for anything. Even if you’re an experienced MongoDB user, it pays to polish up your knowledge base.

Master the skills of data modeling, ingestion, query and sharding with the MongoDB Developer and Administration Certification training course.

MongoDB Interview Questions

1. What Is MongoDB?

MongoDB is a cross-platform document-oriented database program that offers high performance, high availability and easy scalability. It is considered the leading NoSQL database.

2. What’s a NoSQL Database, What Types Are There, and What Type Is MongoDB?

A NoSQL database offers a mechanism for storage and retrieval of data meant to respond to the unique demands and challenges of today’s modern applications. NoSQL, which stands for “Not Only SQL” is a departure from the tabular relations used in relational databases such as SQL and Oracle.

Types of NoSQL databases:

  • Document-oriented
  • Key-Value Stores
  • Graph Stores
  • Wide-Column Stores

MongoDB is the first type, a document-oriented database, storing data in Binary JSON (BSON) structure-based documents, which in turn are stored in a collection.

3. What Is MongoDB Best Suited For?

MongoDB is a Relational Database Management System (RDBMS) replacement for web applications, giving users the additional partition tolerance that RDMS doesn’t provide. MongoDB is suitable for real-time analytics and high-speed logging and is highly scalable. It’s perfect for handling unstructured, complicated, and messy data.

MongoDB is used by an impressively wide variety of organizations today, including Google, Cisco, Verizon, Nokia, and Facebook, to name a few.

4. What Advantages Does MongoDB Offer over Other Similar Programs?

MongoDB provides a highly flexible and scalable document structure. For instance, one data document in MongoDB can have six columns while other documents in the same collection can have a dozen columns. Furthermore, thanks to efficient indexing and storage techniques, MongoDB databases are faster in comparison with other SQL databases.

5. What Are the Drawbacks Of MongoDB?

The 32-bit edition has a 2GB data limit (it’s actually 4GB, but 2GB is taken up by the OS). If this limit is somehow exceeded, it will corrupt the entire database and the existing data. This bug doesn’t exist in the 64-bit, and this is the version recommended if you’re doing any serious application work.

MongoDB allows very fast writes and updates by default, but as a result, you are not explicitly notified of any failures. By default, most drivers do asynchronous, ‘unsafe’ writes, meaning that the driver does not return an error directly, like as in the case of INSERT DELAYED with MySQL. If you want to know if something succeeded, you have to personally check for errors using the get last error function. If there is a server crash or power failure, all changes buffered in the memory will be lost. Although this functionality can be disabled, it will reduce performance to the equivalent of MySQL, and possibly worse.

MongoDB is ideal only for implementing things like analytics/caching, where the impact of small data loss is negligible.

MongoDB makes it difficult to represent relationships between data, as JOINS are not possible with it. As a result, you end up performing the task manually by creating another table to represent the relationship between rows in two or more tables.

6. List MongoDB’s Prominent Features.

The most important MongoDB features are:

  • Faster than the standard databases
  • Rich, expressive query language
  • Easily scalable database
  • Very flexible in document forms

7. What Is the Role of Profiler In MongoDB?

MongoDB comes with a database profiler that shows each operation’s performance characteristics against the database. Using the profiler, you can analyze all of the queries which are being run by the DB system in question. This information can then be used for determining when an index is called for.

8. What Languages Can You Use With MongoDB?

The languages MongoDB uses are, in alphabetical order:

  • C
  • C++
  • C#
  • Erlang
  • Go
  • Java
  • Node.js
  • Perl
  • PHP
  • Python
  • Ruby
  • Scala

9. What Is the Role of Namespace in the Context Of MongoDB?

A namespace is the combination (often referred to as the concatenation) of the database name and the collection or index name. For instance, “students.girls” would indicate the database was called “students”, and the collection is “girls”.

10. Explain Sharding in MongoDB.

Sharding is the procedure of storing data on multiple machines. It’s how MongoDB deals with the issue of increased data growth demands. This data storage method involves the horizontal partitioning of data in a search engine or database; each partition is known as a shard or a database shard.

11. What Is CRUD?

This is an acronym for Create, Read, Update, and Delete the basic MongoDB operations.

12. If You Remove a Document from the Database, Will Mongodb Also Remove It from the Disk?

Yes. Removing a document from the database results in it being removed from the disk as well.

13. Talk about Replication in MongoDB. What Is It, and Why Is It Important?

The process of synchronizing data across multiple servers is known as replication. The process increases data availability and offers redundancy, which in turn protects the database from the loss of a single server. Thus, replication allows for faster recovery from service interruptions or hardware failures.

14. You’re Creating a Schema in MongoDB. What Points Do You Need to Keep in Mind?

The points you need to take into consideration when creating schema are:

  1. You must design your schema according to the user’s (or your) requirements.
  2. Objects are used together should be combined into one document. If they aren’t, then keep them separate.
  3. Do your joins while writing, and not when it is on reading.
  4. Optimize your schema for most frequent use cases.
  5. Perform your complex aggregation in the schema.

15. Discuss the Differences Between MySQL and MongoDB.

While both databases are free and open-source, there are some significant divergences. For instance, MySQL represents data in the form of rows and tables, while the data in MongoDB is represented as collections of JavaScript Object Notation (JSON) documents.

Furthermore, when performing a query, strings get put into the query language that the database system then parses. In fact, the language is called Structured Query Language (SQL) and yes, that’s where MySQL gets its a name.

MongoDB uses object querying; you just pass a document to MongoDB detailing what you’re querying; no parsing at all.

In terms of transactions, MySQL supports atomic transactions, which are defined as having the ability to run multiple operations within one transaction; on the other hand, MongoDB doesn’t support transactions; the single operation is atomic.

When using MySQL, you need to define the schema, but MongoDB doesn’t require it. So in the former case, you need to define the columns and tables, whereas in the latter case, you just drop in the documents and you’re good. If you are keen on conducting performance testing and analysis, then MySQL is your best bet, since MongoDB has no reporting tools.

Finally, in MySQL, the relational database is the only JOIN operation which permits conducting queries across multiple tables. In contrast, MongoDB doesn’t support the JOIN operation, but it can support multi-dimensional data types. As a result of this lack of JOIN support, MongoDB performs better than databases like MySQL.

16. What Does the Objectld Consist Of?

Objectld is made up of a:

  • Timestamp
  • Client machine ID
  • Client process ID
  • 3 byte incremented counter

Want to Learn More about MongoDB?

Whether you’re preparing for an interview or simply upskilling, Simplilearn offers you the training you need to advance your career in MongoDB. With the MongoDB Developer and Administrator Certification training course, you can become an expert MongoDB developer and administrator, gaining an in-depth knowledge of NoSQL and mastering skills of data modeling, ingestion, query, sharding, and data replication.

The course is offered as self-paced learning, online classroom Flexi-Pass, or as a corporate training solution, and includes 32 hours of instructor-led training, three industry-based projects in e-learning and telecom domains, 17 hours of self-paced video, and a half-dozen lab exercises conducted on a virtual machine.

The course is best suited for database administrators, software developers, system administrators, and analytics professionals. Once you complete an assigned project and pass the online certification exam, you will be a certified MongoDB professional.

Take a look at what Simplilearn can do for you before you take the first step into this challenging but rewarding field.

About the Author

John TerraJohn Terra

John Terra lives in Nashua, New Hampshire and has been writing freelance since 1986. Besides his volume of work in the gaming industry, he has written articles for Inc.Magazine and Computer Shopper, as well as software reviews for ZDNet. More recently, he has done extensive work as a professional blogger. His hobbies include running, gaming, and consuming craft beers. His refrigerator is Wi-Fi compliant.

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