$Consistency

A transaction must transform the database from one consistent state to another consistent state.

Nov 17, 2025

Consistency ensures that a database transaction brings the database from one valid state to another valid state, maintaining all defined rules and constraints.

• Integrity constraints must be satisfied before and after the transaction (Eg: Foreign keys constraints)
• Business rules encoded in the database are enforced
• If a transaction violates consistency rules, it’s rolled back

Example

If you transfer £200 between bank accounts, consistency ensures:

Both accounts exist

• The sender has sufficient funds
• Total money in the system remains the same
• All constraints (positive balance, valid account types) are maintained

Consistency vs Atomicity

Atomicity handles completeness of execution, Consistency handles correctness of the result.

Further Reading

• Designing Data-Intensive Applications