Question

Q4: Define transactions in DBMS. Briefly explain each of the ACID properties of a transaction

Answer 1

A transaction can be defined as a logical unit of work on the database. This may be an entire program, a piece of a program, or a single command (like the SQL commands such as INSERT or UPDATE), and it may engage in any number of operations on the database. In the database context, the execution of an application program can be thought of as one or more transactions with non-database processing taking place in between.

ACID PROPERTIES are used for maintaining the integrity of database during transaction processing. ACID stands for Atomicity, Consistency, Isolation, and Durability.

• Atomicity: A transaction is a single unit of operation. You either execute it entirely or do not execute it at all. There cannot be partial execution.
• Consistency: Once the transaction is executed, it should move from one consistent state to another.
• Isolation: Transaction should be executed in isolation from other transactions (no Locks). During concurrent transaction execution, intermediate transaction results from simultaneously executed transactions should not be made available to each other. (Level 0,1,2,3)
• Durability: · After successful completion of a transaction, the changes in the database should persist. Even in the case of system failures.