NoSQL

NoSQL (Not Only SQL) databases abandon the rigid relational model to achieve horizontal scalability, flexible schemas, and high availability at internet scale.

MongoDB is the world's most popular document database. It stores data as BSON (Binary JSON) documents in collections (analogous to tables). Each document can have a different structure — true schema f

Advanced MongoDB topics that differentiate production-grade implementations from beginner ones.

Redis (Remote Dictionary Server) is an in-memory data structure store used as a database, cache, message broker, and streaming engine. Sub-millisecond latency makes it ideal for caching, sessions, lea

Apache Cassandra is a distributed wide-column database designed for high-write throughput, linear scalability, and no single point of failure. Used by Netflix, Apple, Discord, and Instagram.

Neo4j is the world's leading graph database. It stores data as nodes (entities) and relationships (edges), making it ideal for connected data where relationships are first-class citizens.

Understanding distributed database concepts is essential for designing scalable systems and answering architecture interviews. These concepts underpin all NoSQL databases.

System design patterns for caching and data consistency are essential for senior engineering interviews. Understanding when and how to apply each pattern separates junior from senior engineers.