Transactions

Question 1

What is a transaction?

Answer 1

a single logical unit of work that must be entirely completed or aborted.

Question 2

Name the transaction properties

Answer 2

1. Atomicity
2. Consistency
3. Isolation
4. Durability

Question 3

define Atomicity.

Answer 3

all database operations (sql requests) of a transaction must be entirely completed or entirely aborted.

Question 4

Define Consistency

Answer 4

it must take the database from one consistent state to another

Question 5

Define Isolation

Answer 5

• it must not interfere with other concurrent transactions.
• Data used during execution of a transaction cannot be used by a second transaction until the first one is completed.

Question 6

Define Durability

Answer 6

Once completed the changes the transaction made to the data are durable, even in the event of system failure.

Question 7

What is serializability

Answer 7

• ensures that the schedule for the concurrent execution of several translations should yield consistent results.

Question 8

What is a transaction log.

Answer 8

keeps track of all transactions in the database.
- recovery requirements triggered by Rollback Statement.
- Program’s abnormal termination.
- System Failure.

Question 9

what is Concurrency Control.

Answer 9

A method used to manage simultaneous operations without conflicts.

Question 10

Three Main problems associated with Concurrency Control

Answer 10

1. Lost update
2. Uncommitted data.
3. Inconsistency Retrievals

Question 11

Define lost update.

Answer 11

• Occurs in two concurrent transactions when : same data element is updated and one of the updates is lost.

Question 12

Define Uncommitted data.

Answer 12

• occurs when 2 transactions are executed concurrently, first transaction is rolled back after the second transaction has accessed uncommitted data.

Question 13

Define Inconsistency Retrievals

Answer 13

• occurs when a transaction accesses data before and after one or more other transactions finish working with such data.