🍃 MongoDB Interview Questions and Answers (2025)
Basic Level Questions
What is MongoDB?▶
MongoDB is a popular open-source NoSQL document-oriented database that stores data in BSON format, suitable for handling large volumes of unstructured data.
What is a document in MongoDB?▶
A document is a basic unit of data in MongoDB, stored in JSON-like BSON format, consisting of field and value pairs.
What is a collection?▶
A collection is a group of MongoDB documents, analogous to tables in relational databases.
What is the primary key in MongoDB?▶
The primary key is the _id field which uniquely identifies each document in a collection.
How does MongoDB differ from relational databases?▶
MongoDB uses flexible schema documents, supports horizontal scaling, and omits SQL’s rigid relational schemas and joins.
What is BSON?▶
BSON is a binary-encoded JSON-like format used internally by MongoDB for data storage and network transfer.
What query language does MongoDB use?▶
MongoDB uses its own rich and expressive query language based on JSON-style query documents.
What are indexes in MongoDB?▶
Indexes improve query performance by creating data structures that allow fast search on specific fields.
What is the purpose of replication in MongoDB?▶
Replication provides data redundancy and high availability by maintaining multiple copies of data across replica set members.
How does sharding work in MongoDB?▶
Sharding distributes data across multiple servers by partitioning collections based on shard keys, enabling horizontal scaling.
Intermediate Level Questions
What are replica sets?▶
Replica sets are groups of MongoDB servers that maintain the same data set, providing redundancy and automatic failover.
Explain CRUD operations in MongoDB.▶
CRUD stands for Create, Read, Update, and Delete, fundamental operations on documents via MongoDB’s query API.
How does the aggregation framework work?▶
Aggregation framework processes data records and returns computed results using stages like $match, $group, $sort in an aggregation pipeline.
What security features does MongoDB provide?▶
MongoDB offers authentication, role-based access control, encryption at rest and in transit, auditing, and network isolation.
What is the WiredTiger storage engine?▶
WiredTiger is the default storage engine offering document-level concurrency control, compression, and high performance.
How does MongoDB handle transactions?▶
MongoDB supports multi-document ACID transactions, allowing atomic changes across multiple documents and collections.
How do text indexes work?▶
Text indexes enable efficient search within string content using language-aware tokenization and ranking.
Explain capped collections.▶
Capped collections are fixed-size collections that preserve insertion order and behave like circular queues.
How does TTL index work?▶
TTL (Time To Live) index automatically removes documents after a specified period for managing data lifecycle like session expiration.
What is the difference between $lookup and $graphLookup?▶
$lookup performs left outer join between collections; $graphLookup performs recursive search on a collection to find related documents.
What is aggregation pipeline optimization?▶
Explain change streams in MongoDB.▶
How to manage schema design in MongoDB?▶
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