1. Transaction Properties
All operations of a transaction must be completed
If not, the transaction is aborted
Atomicity
Permanence of database’s consistent state
Consistency
Data used during transaction cannot be used by second transaction until the first is completed
Isolation
Ensures that once transactions are committed, they cannot be undone or lost
Durability
Ensures that the schedule for the concurrent execution of several transactions should yield consistent results
Serializability

2. A Transaction Log

3. Two concurrent transactions to update QOH
Serial execution of the two transactions

4. Lost updates

5. Transactions creating an uncommitted data problem

6. Correct execution of two transactions
Serial execution of these transactions yields the correct result

7. Another uncommitted data problem
This time the problem occurs because the rollback is completed after T2 has started.

8. Inconsistent retrievals: Retrieval during update

9. Inconsistent retrievals:

10. Database-Level Lock

11. Table-level lock

12. A Page level lock

13. A row-level lock

14. Lock Types Binary lock Exclusive lock Shared lock
Has two states, locked (1) and unlocked (0)
If an object is locked by a transaction, no other transaction can use that object
If an object is unlocked, any transaction can lock the object for its use
Binary lock
Exists when access is reserved for the transaction that locked the object
Exclusive lock
Exists when concurrent transactions are granted read access on the basis of a common lock
Shared lock

15. Using a binary lock

16. Figure 10.7 - Two-Phase Locking Protocol

17. Table 10.13 - How a Deadlock Condition is Created

18. Table 10.14 - Wait/Die and Wound/Wait Concurrency Control Schemes

19. Transaction recovery example