Wavelength Intermediate: Workbook with key

The transaction is aborted and the results of the first two bookings are undone — the airline data base is restored to the value it had before the transaction started [see Fig. 3-16(b)]. It is as though nothing happened. Fig. 3-16. (a) Transaction to reserve three flights commits. (b) Transaction aborts when third flight is unavailable. Properties of Transactions Transactions have four essential properties. Transactions are: 1. Atomic: To the outside world, the transaction happens indivisibly. 2. Consistent: The transaction does not violate system invariants. 3. Isolated: Concurrent transactions do not interfere with each other. 4. Durable: Once a transaction commits, the changes are permanent. These properties are often referred to by their initial letters, ACID. The first key property exhibited by all transactions is that they are atomic. This property ensures that each transaction either happens completely, or not at all, and if it happens, it happens in a single indivisible, instantaneous action. While a transaction is in progress, other processes (whether or not they are themselves involved in transactions) cannot see any of the intermediate states ...»