Transaction Management

Question 1

What is a transaction?

Answer 1

A transaction is an operation (or operations) onto a database such as a write operation.

Question 2

What is the purpose of transactions having the atomicity property?

Answer 2

Atomicity is the property that a transaction is conducted with no intermediate steps. This means that if the transaction fails, all operations in the transaction are cancelled meaning the database returns to its state pre-transaction. Thus, there is no room for data inconsistency errors.

Question 3

What is the acronym for the 4 transaction properties? Define each property…

Answer 3

Atomicity : A transaction with multiple operations is conducted in a single unit. This helps prevent conflicting operations.
Consistency : Transactions act within the constraints of the database.
Isolation : Transactions are conducted in isolation of one another, meaning they can occur concurrently.
Durability : Transactions maintain regardless if system crashes.

Question 4

Define scheduling in regards to database transactions…

Answer 4

Scheduling is the way in which concurrent transactions are conducted on a database

Question 5

What are the 2 types of schedule? Define each..

Answer 5

Serial : Concurrent operations are not interleaved. Not recommended.
Non serial : Concurrent operations are interleaved.

Question 6

Which type of scheduling is preferred?

Answer 6

Non-serial is preferred.

Question 7

What are the 2 main desired properties of a schedule?

Answer 7

Serializability and Recoverability

Question 8

What is the purpose of serializability?

Answer 8

Serializability ensures atomicity in order to prevent conflicting operations.

Question 9

How do we test for serializability?

Answer 9

1. Create a precedence graph.
2. Test for cycle.