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Data & Analytics · Foundational

Consistency (ACID)

The ACID property that a transaction takes the database from one valid state to another, respecting all constraints and rules.

Definition

Consistency means a committed transaction never leaves constraints, keys or triggers violated. It is different from the 'C' in the CAP theorem, which refers to all nodes seeing the same latest data.

Example

A transaction that would create an order for a nonexistent customer is rejected by the foreign key.

Exam tip

ACID consistency = valid state under the rules; CAP consistency = every read sees the latest write.

Related terms