What is the technical difference between Postgres and Redis? What are the principles of ACID?

Postgres is a relational database management system (RDBMS) with support for complex queries, transactions, and ACID properties. Redis is an in-memory key-value store, often used as a cache or message broker.

Technical differences:

• Postgres stores data on disk, supports complex SQL queries, indexes, transactions.
• Redis stores data in memory, provides very fast performance, but is limited in data volume, supports data structures (strings, lists, sets, etc.).

ACID is a set of principles for transactional systems:

• Atomicity: a transaction is either fully completed or not executed at all.
• Consistency: after a transaction, the database remains in a correct state.
• Isolation: parallel transactions do not affect each other.
• Durability: after a transaction is committed, its changes are saved even in case of failures.

Postgres supports ACID, Redis partially (for example, by default it does not guarantee durability, but it can be configured).