Question

In the context of concurrent database transactions, a transaction must possess three characteristics. In the space below, give a short description for each of these characteristics.

I am having trouble finding this in Database System Concepts fourth 6th edition. Author is Abraham Silberschatz.

I think this is the answer, but I am unsure:

1. Transaction Processing
2. Management of concurrent transactions
3. Failure Recovery

Answer 1

In database there are many resources which can be shared mutually among various processes at the same time. For example, Banking system, airline reservation systems and so on. Concurrent execution of the same transaction can affect the performance and at the same time can result in deadlock. There are various states of a database transaction which are listed below

1. Active: Database transaction enter this state when execution begins. Read or write can be performed during this state.
2. Partially Committed: A database transaction enters into this state after end of a transaction.
3. Committed state: This state implies that transaction has completed successfully. All the changes are recorded to the database permanently
4. Failed state: A transaction is treated as failed, if transaction is aborted or any checks have been failed
5. Terminated state: A transaction enters into terminated state if certain transactions which are leaving the system cannot be restarted.

For marinating the concurrency of database transactions. Each and every transaction is expected to possess the below mentioned characteristics.

Atomicity:

Every transaction should be considered as a two-phase execution unit. Either it should be executed completely or it should not be executed at all. There is no room for partial execution.

Consistency:

Once transaction is executed, it should move from one consistent state to another (states have been explicitly stated above)

Isolation:

Isolation means that data used during the processing of one transaction cannot be shared with another transaction until and unless the first transaction is complete. Second transaction should wait until it is accessing the data alone.

Durability:

Durability means that a committed transaction continues to remain in the same state even after a system failure. If a transaction is under process, then effects are not permanent .In the casualty of database failure, backups should be able to restore consistent state of transaction