What are the main differences between PostgreSQL, MongoDB, and Redis in terms of architecture and usage?

PostgreSQL, MongoDB, and Redis are different data storage systems with different architectures and purposes:

1. PostgreSQL

• Relational DBMS (SQL).
• Stores data in tables with a strict schema.
• Supports complex queries, transactions, and relationships between tables.
• Used for systems where data integrity and complex operations are important.

2. MongoDB

• Document-oriented NoSQL database.
• Stores data in JSON-like documents (BSON).
• Flexible schema, easily scalable.
• Suitable for applications with changing data structures.

3. Redis

• In-memory key-value store.
• Very fast, supports data structures (strings, lists, sets).
• Used for caching, sessions, queues.
• Not intended for long-term storage of large volumes of data.

Thus, the choice depends on the requirements: PostgreSQL for complex relational data, MongoDB for flexible documents, Redis for fast access and caching.