Mastering MongoDB Interviews: Top 80 Questions and Answers

MongoDB, the renowned document-oriented database, has gained immense popularity due to its ability to handle large volumes of data efficiently. As its adoption continues to rise, the demand for skilled MongoDB professionals is skyrocketing. To help you excel in your MongoDB interview, we’ve curated a comprehensive collection of 80 top MongoDB interview questions and answers.

Basic MongoDB Interview Questions

1. What is MongoDB?
   MongoDB is a cross-platform, document-oriented, NoSQL database. It stores data in flexible, JSON-like documents with dynamic schemas, making it easier to integrate data in certain types of applications.

2. What are the key features of MongoDB?
   The key features of MongoDB include:

   • Document-oriented data model
   • High performance
   • High availability
   • Easy scalability
   • Rich query language

3. What type of NoSQL database is MongoDB?
   MongoDB is a document-oriented NoSQL database. It stores data in BSON (Binary JSON) documents, which are organized into collections.

4. Explain the concept of a Namespace in MongoDB.
   A namespace in MongoDB is the concatenation of the database name and the collection name, used to uniquely identify a collection within a database.

5. If you remove an object attribute, is it deleted from the database?
   Yes, if you remove an object attribute, it is deleted from the database. It’s recommended to remove the attribute and then save the object again.

6. How can you move old files into the moveChunk directory?
   During shard balancing operations, old files are converted to backup files and moved to the moveChunk directory. These files can be deleted once the operations are complete.

7. Explain the situation when an index does not fit into RAM.
   When an index is too large to fit into RAM, MongoDB reads the index from disk, which is slower than reading from RAM. However, if the server has enough RAM for indexes and the working set, indexes can easily fit into RAM.

8. How does MongoDB provide consistency?
   MongoDB uses reader-writer locks, allowing concurrent readers to access any resource like a database or collection while providing exclusive access to a single writer at a time.

9. Why is MongoDB not chosen for a 32-bit system?
   MongoDB is not recommended for a 32-bit system because running a 32-bit MongoDB server limits the total storage size (data and indexes) to 2GB. For production deployments, 64-bit builds and operating systems are strongly recommended.

10. How does Journaling work in MongoDB?
    Write operations are saved in memory while journaling is in progress. The on-disk journal files are reliable because journal writes are sequential. MongoDB creates a journal subdirectory within the dbPath.

11. How can you isolate cursors from intervening with write operations?
    The snapshot() method is used to isolate cursors from intervening with writes. It establishes a coherent view of the data and ensures that each query sees any document only once.

12. Define MongoDB.
    MongoDB (from “humongous”) is a cross-platform, document-oriented database. Classified as a NoSQL database, MongoDB uses JSON-like documents with dynamic schemas (called BSON) instead of traditional table-based relational database structures, making data integration easier and faster in certain types of applications.

13. What is a Replica Set in MongoDB?
    A replica set is a group of MongoDB instances that maintain the same data set. Replica sets provide redundancy and high availability and are the basis for all production deployments.

14. What is CRUD in MongoDB?
    MongoDB provides CRUD (Create, Read, Update, Delete) operations:

    • Create: db.collection.insert(document)
    • Read: db.collection.find()
    • Update: db.collection.update()
    • Delete: db.collection.remove()

15. What is Sharding in MongoDB?
    In MongoDB, sharding means to store data on multiple machines to support deployments with large data sets and high throughput operations.

16. What is Aggregation in MongoDB?
    In MongoDB, aggregations are operations that process data records and return computed results.

Intermediate MongoDB Interview Questions

1. Which syntax is used to create a Collection in MongoDB?
   We can create a collection in MongoDB using the following syntax:
   db.createCollection(name, options)

2. Which syntax is used to drop a Collection in MongoDB?
   We can use the following syntax to drop a collection in MongoDB:
   db.collection.drop()

3. Explain Replication in MongoDB.
   Replication is the process of synchronizing data across multiple