It means that either all changes within a single transaction occur or none of them occur.
The transactions should be atomic even if the transaction is interrupted by an operating system crash or power failure.
Atomic commit is implemented via a rollback journal
Hardware and Atomicity
Atomic commit cannot be implemented with the hardware disk because:
- a transaction may write data in different sector (different place)
- writing a single sector is serial and takes a finite amount of time
- the action can't therefore be instantaneous
Therefore the application needs to creates the illusion of atomic commit (ie the transactions appear to be atomic)