Four distinct responsibilities
Atomicity makes protected changes complete or cancel together. Durability concerns preserving acknowledged commits through specified failures. One addresses interruption before completion; the other addresses survival afterward.
Consistency concerns applicable data constraints and business invariants, while isolation limits interference among concurrent transactions. A database enforces declared rules, but the application must correctly express its business operation and choose its transaction boundary.
Mechanisms cooperate to provide guarantees
Logging and recovery support undo or redo; locks, versions, and conflict detection coordinate concurrency; declared constraints limit acceptable data. No single logging technique supplies every property on its own.
Products expose different isolation and commit modes. PostgreSQL Read Committed does not promise serializable execution for every workload, and asynchronous commit can lose recently acknowledged work in a crash. Configuration is therefore part of the effective guarantee.
Consistency has a defined scope
ACID consistency does not certify that records match the real world, nor does it name every consistency model for distributed replicas. Incorrect rules or missing checks can still admit erroneous business results.
A transaction in one database does not automatically roll back a remote service or a delivered notification. Designers must identify participating resources and coordinate external effects and retries. The four properties frame these questions rather than replace their answers.