ACID

Question 1

Atomicity

Answer 1

By this, we mean that either the entire transaction takes place at once or doesn’t happen at all. There is no midway i.e. transactions do not occur partially. Each transaction is considered as one unit and either runs to completion or is not executed at all. It involves the following two operations.
— Abort : If a transaction aborts, changes made to the database are not visible.
— Commit : If a transaction commits, changes made are visible.
Atomicity is also known as the ‘All or nothing rule’.

Question 2

Consistency

Answer 2

Consistency ensures that a database remains in a valid state before and after a transaction. It guarantees that any transaction will take the database from one consistent state to another, maintaining the rules and constraints defined for the data.

Question 3

Isolation

Answer 3

This property ensures that multiple transactions can occur concurrently without leading to the inconsistency of the database state. Transactions occur independently without interference. Changes occurring in a particular transaction will not be visible to any other transaction until that particular change in that transaction is written to memory or has been committed. This property ensures that when multiple transactions run at the same time, the result will be the same as if they were run one after another in a specific order.

Question 4

Durability

Answer 4

This property ensures that once the transaction has completed execution, the updates and modifications to the database are stored in and written to disk and they persist even if a system failure occurs. These updates now become permanent and are stored in non-volatile memory. The effects of the transaction, thus, are never lost.