CBSE Class 12 Informatics Practices Database Transactions Assignment

SOLVED QUESTIONS

1. Define a transaction.

Ans. -A transaction is a logical unit of a work that must succeed or fail in its entirely. It is an atomic operation which can be divided unto smaller operations.

2. What are the two ways in which multiple transactions can be executed?

Ans. - Multiple transactions can be executed in one of the following two ways:

(i) Serially (ii) Concurrently

3. What is a savepoint?

Ans. - Savepoints are special operations that allow you to divide the work of a transaction into different segments. In case of a failure, you can execute rollbacks to the savepoint only, leaving prior changes intact.

4. What to you understand by a database transaction?

Ans. - A database transaction is a logical unit of work that must succeed or fail in its entirely.

5. Why do understand by transaction COMMIT and ROLLBACK?

Ans-COMMITing a transaction means all the steps of a transaction are carried out successfully and all data changes are made permanent in the database. Transaction ROLLBACK means transaction has not been finished completely and hence all data changes made by the transaction in the database if any, are undone and the database returns to the state as it was before this transaction execution started.

6. What do you understand by ACID properties of database transaction?

Ans. -To ensure the data-integrity, the database system maintains the following properties of transaction. The properties given below are termed as ACID properties-an acronym derived from the first letter of each of the properties.

(i) Atomicity-This property ensures that either all operations of the transactions are reflected properly in the database, none are. Atomicity ensures either al-or-none operations of a transaction are carried out.

(ii) Consistency-This property ensures that database remains in a consistent state before the start of transaction and after the transaction is over.

(iii) Isolation-Isolation ensures that executing transaction execution in isolation i.e. is unaware of other transactions executing concurrently in the system.

(iv) Durability-This property ensures that after the successful completion of a transaction i. e when a transaction COMMITs, the changes made by it to the database persist i. e remain in the database irrespective of other failures.

7. What the function is of redo and undo logs?

Ans. -Every database has a set of redo log files. It records all change in data including both committed and uncommitted changes. Undo logs stored roll backed data.

8. What TCL commands are supported by SQL?

Ans. -SQL supports following TCL commands 

• BEGIN |START TRANSACTION-Marks the beginning of a transaction

• COMMIT-Ends the current transaction by saving database changes and starts a new transaction. 

• ROLLBACK-Ends the current transaction by discarding changes and starts a new transaction. 

• SAVEPOINT-Defines breakpoints for the transactions to allow partial rollbacks. 

• SET AUTOCOMMIT-Enables or disable the default autocommit mode.

9. Which two statements complete a transaction?

A. DELETE employees;

B. DESCRIBE employees;

C. ROLLBACK TO SAVEPOINT C;

D. GRANT SELECT ON employees TO SCOTT;

E. ALTER TABLE employees

MODIFY COLUMN sal;

F. Select MAX(sal)

FROM employees

WHERE department_id=20;

Ans. - C, E

UNSOLVED QUESTIONS

1. What is the benefit of transaction?

2. What are the five states of the transactions?

3. What will happen when COMMIT statement is issued?

4. What will happen when ROLLBACK statement is issued?

5. How can you start a new transaction?