the actual writes only after the transaction enters the committed state

The text below is from Database System Concepts by Silberschatz. It says that the actual writes take place only after the transaction enters the committed state. **My question**: When the transaction has entered the committed state, there's no more statement to be executed, so who will perform these actual writes? > We must be cautious when dealing with observable external writes, such as writes to a user’s screen, or sending email. Once such a write has occurred, it cannot be erased, since it may have been seen external to the database system. Most systems allow such writes to take place only after the transaction has entered the committed state. One way to implement such a scheme is for the database system to store any value associated with such external writes temporarily in a special relation in the database, and to perform the actual writes only after the transaction enters the committed state. If the system should fail after the transaction has entered the committed state, but before it could complete the external writes, the database system will carry out the external writes (using the data in non-volatile storage) when the system is restarted.