Atomicity means a database transaction takes effect in full or not at all. It is the all-or-nothing property in ACID, the set of guarantees used to provide safe transactional behavior. section 9.4
Atomicity does not replace the other ACID guarantees:
- Consistency preserves database invariants, such as constraints and triggers. section 9.4
- Isolation keeps concurrent transactions from interfering with one another. section 9.4
- Durability preserves committed effects through a system failure. section 9.4
These guarantees have different performance costs. Serializable isolation can require extensive locking or validation, while durability can require synchronous writes to persistent storage. Neither cost describes how atomicity itself is implemented. section 9.4
Do not confuse transaction atomicity with a processor atomic operation. An atomic load, store, or read-modify-write acts as one indivisible step relative to other threads; such operations are building blocks for synchronization, not an all-or-nothing guarantee for an entire database transaction. section 8.3 section 8.3.1
