Understanding ACID in Databases

What does the 'A' in ACID stand for in database transactions?

• Accuracy

• Atomicity

• Accessibility

• Adaptability

Answer explanation

The 'A' in ACID stands for Atomicity, which ensures that a series of database operations are completed as a single unit. If any operation fails, the entire transaction is rolled back, maintaining data integrity.

Which of the following best describes Atomicity in the context of ACID?

• Transactions are completed in parts.

• A transaction is treated as a single, indivisible unit.

• Transactions can be reversed partially.

• Transactions are always visible to all users.

Answer explanation

Atomicity ensures that a transaction is treated as a single, indivisible unit, meaning it either completes fully or not at all. This prevents partial transactions, making the correct choice "A transaction is treated as a single, indivisible unit."

Why is Consistency important in database transactions?

• It ensures transactions are fast.

• It ensures transactions leave the database in a valid state.

• It allows transactions to be visible to all users immediately.

• It allows transactions to be partially completed.

Answer explanation

Consistency is crucial in database transactions as it ensures that all transactions leave the database in a valid state, maintaining data integrity and preventing corruption.

Which of the following is an example of Consistency in a database?

• A transaction that updates multiple tables simultaneously.

• A transaction that adheres to all defined rules and constraints.

• A transaction that can be reversed at any time.

• A transaction that is visible to all users immediately.

Answer explanation

Consistency in a database ensures that a transaction adheres to all defined rules and constraints, maintaining the integrity of the data. Thus, the correct choice is a transaction that adheres to all defined rules and constraints.

What does Isolation ensure in the context of ACID properties?

• Transactions are completed in parts.

• Transactions do not interfere with each other.

• Transactions are always visible to all users.

• Transactions can be reversed partially.

Answer explanation

Isolation ensures that transactions do not interfere with each other, allowing them to execute independently. This prevents issues like dirty reads and ensures data integrity during concurrent transactions.

Which of the following scenarios illustrates Isolation?

• Two users can update the same account simultaneously without waiting.

• One transaction waits for another to finish before accessing the same data.

• Transactions are visible to all users immediately.

• Transactions can be reversed at any time.

Answer explanation

Isolation in transactions means that one transaction must wait for another to complete before accessing the same data. This prevents conflicts and ensures data integrity, making 'One transaction waits for another to finish' the correct choice.

What does the 'D' in ACID stand for?

• Dependability

• Durability

• Divisibility

• Discrepancy

Answer explanation

The 'D' in ACID stands for Durability, which ensures that once a transaction is committed, it remains so, even in the event of a system failure. This is crucial for maintaining data integrity in databases.

Why is Durability important in database transactions?

• It ensures transactions are fast.

• It ensures committed transactions remain permanent.

• It allows transactions to be visible to all users immediately.

• It allows transactions to be partially completed.

Answer explanation

Durability is crucial because it ensures that once a transaction is committed, it remains permanent, even in the event of a system failure. This guarantees data integrity and reliability in database operations.

Which of the following is an example of Durability?

• A transaction that can be reversed at any time.

• A transaction that is saved to non-volatile storage after being committed.

• A transaction that is visible to all users immediately.

• A transaction that updates multiple tables simultaneously.

Answer explanation

Durability ensures that once a transaction is committed, it remains permanent even in the event of a system failure. Thus, a transaction saved to non-volatile storage after being committed exemplifies durability.

What is the primary purpose of the ACID properties in databases?

• To ensure transactions are completed quickly.

• To prevent data corruption and ensure data integrity.

• To allow transactions to be visible to all users immediately.

• To allow transactions to be partially completed.

Answer explanation

The primary purpose of ACID properties is to prevent data corruption and ensure data integrity during transactions, making sure that all operations are completed successfully or not at all.