ACID is a set of transaction guarantees: atomicity, consistency, isolation, and durability. A transaction is one or more statements applied to a database. section 1.2.2
The four guarantees describe what should happen when database operations succeed, fail, or run concurrently:
- Atomicity means every statement in a transaction succeeds together or fails together. section 1.2.2
- Consistency means the database remains in a valid state after every transaction. section 1.2.2
- Isolation means a transaction cannot interfere with a concurrently executing transaction. section 1.2.2
- Durability means changes made by a transaction persist. section 1.2.2
ACID favors correctness and durable writes. ScyllaDB instead uses BASE—basic availability, soft state, and eventual consistency—which supports faster writes but requires developers to account for weaker consistency. section 1.2.2 section 1.4
Concurrent bank-account operations
Bank-account updates illustrate why isolation matters: concurrent operations without isolation can make the database’s reported balance differ from the amount actually available. Financial data may therefore favor a relational database with stronger ACID transactions. section 1.2.7
