In the Try phase, the wallet service, which acts as the coordinator, sends two transaction commands to two databases:

For the database that contains account A, the coordinator starts a local transaction that reduces the balance of A by $1.

For the database that contains account C, the coordinator gives it a NOP (no operation.) To make the example adaptable for other scenarios, let’s assume the coordinator sends to this database a NOP command. The database does nothing for NOP commands and always replies to the coordinator with a success message.

The Try phase is shown in Figure 7. The thick line indicates that a lock is held by the transaction.