MongoDB Interview Questions and Answers
Freshers / Beginner level questions & answers
Ques 1. What is MongoDB?
MongoDB is a NoSQL database that provides high performance, high availability, and easy scalability. It stores data in flexible, JSON-like documents called BSON.
Ques 2. Explain the structure of a MongoDB document.
A MongoDB document is a JSON-like data structure composed of field-value pairs. Fields may contain other documents, arrays, and arrays of documents.
Ques 3. What is BSON?
BSON is a binary representation of JSON-like documents that MongoDB uses to store data. It adds support for data types like Date and Binary that are not natively supported in JSON.
Ques 4. What is a NoSQL database?
NoSQL databases are databases that provide a mechanism for storage and retrieval of data that is modeled in ways other than the tabular relations used in relational databases.
Ques 5. What is a MongoDB collection?
A collection in MongoDB is a group of MongoDB documents. It is equivalent to an RDBMS table.
Ques 6. What is the significance of the ObjectId in MongoDB?
ObjectId is a 12-byte identifier typically employed as the primary key in a MongoDB document. It consists of a timestamp, machine identifier, process ID, and a random incrementing value.
Ques 7. What is the purpose of the `findOne` method in MongoDB?
The `findOne` method in MongoDB is used to retrieve a single document that satisfies the specified query criteria. It returns the first document that matches the query.
Intermediate / 1 to 5 years experienced level questions & answers
Ques 8. What is indexing in MongoDB?
Indexing is the process of creating an index (like in a book) to improve the performance of queries. Indexes are used to quickly locate and access the data.
Ques 9. What is sharding in MongoDB?
Sharding is the process of distributing data across multiple servers. It is MongoDB's approach to meeting the demands of data growth.
Ques 10. Explain replication in MongoDB.
Replication is the process of synchronizing data across multiple servers. It provides redundancy and increases data availability.
Ques 11. What is the role of the profiler in MongoDB?
The profiler is a MongoDB feature that tracks queries executed against the database. It helps in analyzing and optimizing query performance.
Ques 12. How do you perform aggregation in MongoDB?
MongoDB provides the `aggregate` method to perform aggregation operations, such as filtering, grouping, sorting, and projecting data.
Ques 13. Explain the GridFS in MongoDB.
GridFS is a specification for storing and retrieving large files in MongoDB. It divides a file into chunks and stores each chunk as a separate document.
Ques 14. What is the TTL (Time To Live) index in MongoDB?
The TTL index is a special type of index that automatically deletes documents from a collection after a specified amount of time has passed.
Ques 15. How does MongoDB provide high availability?
MongoDB achieves high availability through replica sets, where data is replicated across multiple servers. If one server goes down, another can serve the data.
Ques 16. What is the role of the WiredTiger storage engine in MongoDB?
WiredTiger is the default storage engine in MongoDB. It provides features like compression, document-level locking, and support for multiple storage engines in the same MongoDB deployment.
Ques 17. What is the significance of the Journal in MongoDB?
The Journal in MongoDB is a write-ahead log that helps in recovering data in case of a server crash or failure. It ensures data durability and consistency.
Ques 18. Explain the process of data migration in MongoDB.
Data migration in MongoDB involves transferring data from one database or collection to another. It can be done using tools like `mongodump` and `mongorestore`.
Ques 19. How can you create an index in MongoDB?
You can create an index in MongoDB using the `createIndex` method. For example, `db.collection.createIndex({ field: 1 })` creates an ascending index on the specified field.
Ques 20. Explain the role of the `mongorestore` command in MongoDB.
The `mongorestore` command is used to restore MongoDB backups created with `mongodump`. It imports BSON data into a MongoDB database.
Experienced / Expert level questions & answers
Ques 21. How can you achieve ACID properties in MongoDB?
MongoDB sacrifices ACID properties for performance and scalability. However, it supports multi-document transactions in recent versions to some extent.
Ques 22. What is the use of the `explain` method in MongoDB?
The `explain` method provides information on the query execution plan, helping in optimizing and understanding how a query is executed.
Ques 23. Explain the concept of covered queries in MongoDB.
Covered queries are queries where all the fields in the query are part of an index, and the index itself can fulfill the query requirements, avoiding the need to fetch data from the actual documents.
Ques 24. What is the role of the `$lookup` stage in MongoDB aggregation?
The `$lookup` stage is used in MongoDB aggregation to perform a left outer join between documents from the source and target collections based on a specified condition.
Ques 25. What is the use of the `mongostat` command in MongoDB?
The `mongostat` command provides a real-time view of various MongoDB statistics, such as insert and query rates, memory usage, and more.
Ques 26. How does MongoDB handle transactions?
MongoDB supports multi-document transactions starting from version 4.0. Transactions allow you to perform multiple operations on one or more documents and ensure atomicity and consistency.
Ques 27. What is the Aggregation Pipeline in MongoDB?
The Aggregation Pipeline is a framework in MongoDB for data aggregation. It allows you to process data and transform it using a sequence of stages, such as `$match`, `$group`, and `$project`.
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