The Flat Transaction Model (FTM) is the most common and simplest transaction model. It establishes that only one transaction at any given time is active among other transactions. A lawful question is if we can start another transaction at the same time. There are two ways to do this:

• We can disallow starting another transaction until the first transaction ends. It's very rigid but it guarantees a solid state.
• We can suspend the current transaction and start a new transaction. Once the new transaction finishes, the original transaction is resumed. In this case, the second transaction can commit while the first transaction executes a rollback. The data of the second transaction remains committed anyway.