Durability is the transaction guarantee that committed effects persist permanently. Once a transaction commits, the system must not later withdraw its promise or undo those effects. section 5.3 section 8.0
A useful mental model is a promise: a successful acknowledgment authorizes later actions that depend on it. Durability makes that acknowledgment trustworthy despite component failures. section 8.0
Payment before shipment
An e-commerce application may ship goods after a payment processor confirms collection. If the processor later backtracks because of failure, the goods have shipped without payment; durability prevents that broken promise. section 8.0
Durability is distinct from the other ACID guarantees:
- Atomicity makes a transaction complete entirely or not at all. section 5.3
- Isolation prevents concurrent transactions from interfering, while consistency expresses application-level rules. section 5.3
