Top MongoDB Interview Questions and Answers for Big Data professionals

MongoDB is a cross-platform, open-source, document-oriented NoSQL database. It uses JSON-like documents with dynamic schemas, enabling high scalability and flexibility. It provides features like automatic sharding, replication, and index support, and has a powerful query language with support for aggregation and real-time analytics. It’s used for modern web and mobile applications, IoT, and big data processing.

1. What is MongoDB and what is it used for?
   MongoDB is a NoSQL document-oriented database that stores data in flexible, JSON-like documents. It is used for handling large volumes of structured, semi-structured, and unstructured data in a highly scalable manner.
2. What is a document in MongoDB?
   A document is a basic unit of data in MongoDB, which is a JSON-like data structure that stores fields and values.
3. What is a collection in MongoDB?
   A collection is a grouping of MongoDB documents that are stored in the same place and have a similar structure.
4. What is the difference between MongoDB and SQL databases?
   MongoDB is a NoSQL database that stores data in flexible, JSON-like documents, while SQL databases are relational databases that store data in tables with fixed schemas.
5. What is sharding in MongoDB?
   Sharding is the process of dividing a large MongoDB database into smaller, more manageable parts called shards. This enables MongoDB to handle large amounts of data and scale horizontally.
6. What is replication in MongoDB?
   Replication is the process of synchronizing data across multiple MongoDB servers. This provides redundancy and increases availability in case one server goes down.
7. What is the syntax for inserting a document in MongoDB?
   The syntax for inserting a document in MongoDB is as follows:

db.collection.insertOne({field1: value1, field2: value2, …})

8. What is the syntax for updating a document in MongoDB?
   The syntax for updating a document in MongoDB is as follows:

db.collection.updateOne({filter}, {$set: {field1: value1, field2: value2, …}})

9. What is the syntax for deleting a document in MongoDB?
   The syntax for deleting a document in MongoDB is as follows:

db.collection.deleteOne({filter})

10. How do you create an index in MongoDB?
    You can create an index in MongoDB using the createIndex method, as follows:

db.collection.createIndex({field: 1})

11. What is the difference between a single-field index and a compound index in MongoDB?
    A single-field index indexes a single field in a collection, while a compound index indexes multiple fields in a collection.
12. How do you drop an index in MongoDB?
    You can drop an index in MongoDB using the dropIndex method, as follows:

db.collection.dropIndex({field: 1})

13. What is the difference between a capped collection and a regular collection in MongoDB?
    A capped collection is a fixed-size collection that automatically overwrites old data when the collection becomes full, while a regular collection has no size limit and does not automatically overwrite old data.
14. What is the difference between a read operation and a write operation in MongoDB?
    A read operation retrieves data from the database, while a write operation modifies or adds data to the database.
15. What is the aggregation framework in MongoDB?
    The aggregation framework is a set of MongoDB operations that perform data processing and analysis on a collection.
16. What is the $group operator in MongoDB?
    The $group operator in MongoDB groups documents by a specified field and performs aggregate functions on the grouped data, such as sum, average, or count.
17. What is the $match operator in MongoDB?
    The $match operator in MongoDB filters documents in a collection based on a specified condition.
18. What is the $project operator in MongoDB?
    The $project operator in MongoDB modifies the output of an aggregation operation by selecting specific fields and transforming data.
19. What is the $lookup operator in MongoDB?
    The $lookup operator in MongoDB performs a left outer join between two collections
20. What is the difference between a left outer join and an inner join in MongoDB?
    A left outer join returns all documents from the left collection and matching documents from the right collection, while an inner join only returns matching documents from both collections.
21. What is the difference between $push and $addToSet in MongoDB?
    The $push operator in MongoDB adds an element to an array field in a document, even if it already exists, while the $addToSet operator only adds an element to an array field if it does not already exist.
22. What is the TTL index in MongoDB?
    The TTL index in MongoDB is a special type of index that automatically deletes documents from a collection after a specified amount of time has elapsed.

23.What is the MapReduce function in MongoDB?
The MapReduce function in MongoDB is a data processing function that allows you to perform complex data analysis on a collection.

24. What is the difference between a capped collection and a TTL collection in MongoDB?
    A capped collection is a fixed-size collection that automatically overwrites old data when the collection becomes full, while a TTL collection is a collection that automatically deletes documents after a specified amount of time has elapsed.
25. What is the $unwind operator in MongoDB?
    The $unwind operator in MongoDB deconstructs an array field in a document and outputs one document for each element in the array.
26. What is the difference between a standalone MongoDB deployment and a replica set deployment?
    A standalone MongoDB deployment consists of a single MongoDB instance, while a replica set deployment consists of multiple MongoDB instances that work together to provide high availability and data redundancy.
27. What is the primary node in a MongoDB replica set?
    The primary node in a MongoDB replica set is the node that accepts all write operations and is responsible for replicating data to secondary nodes.
28. What is the purpose of the oplog in MongoDB?
    The oplog in MongoDB is a collection that stores a record of all write operations that have occurred in a replica set. This allows secondary nodes to catch up with the primary node and keep their data in sync.
29. What is a gridFS in MongoDB?
    GridFS is a file storage system in MongoDB that allows you to store and retrieve files that exceed the BSON document size limit of 16MB.
30. What is the difference between the MongoDB shell and a MongoDB driver?
    The MongoDB shell is a command-line interface that allows you to interact with MongoDB using JavaScript commands, while a MongoDB driver is a software library that allows you to interact with MongoDB using programming languages such as Python, Java, or Node.js.

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