ACID Properties in DBMS

ACID properties are one of the most important DBMS interview and viva topics because they explain why transactions in a database stay reliable.

What is a transaction?

A transaction is a logical unit of work in a database.

Example:

• transferring money from one account to another

This may include:

• deduct amount from sender
• add amount to receiver

Both steps should work correctly together.

What is ACID?

ACID stands for:

• Atomicity
• Consistency
• Isolation
• Durability

Atomicity

Atomicity means a transaction should happen completely or not at all.

If one step fails, the full transaction should roll back.

Consistency

Consistency means the database should move from one valid state to another valid state.

Data rules and constraints should remain correct.

Isolation

Isolation means one transaction should not interfere incorrectly with another concurrent transaction.

Durability

Durability means once a transaction is committed, it should remain saved even if system failure happens later.

Simple Example

In online banking:

• if money is deducted from one account
• but system crashes before adding it to another account

then database reliability breaks. ACID properties prevent such problems.

Interview-style answer

ACID properties are transaction reliability properties in DBMS. Atomicity means all-or-nothing execution, Consistency keeps the database valid, Isolation controls concurrent execution safely, and Durability ensures committed data is permanently saved.

Quick Revision Points

• Atomicity = complete or rollback
• Consistency = valid state maintained
• Isolation = safe concurrent execution
• Durability = committed data remains saved

Viva Questions

1. What are ACID properties?
2. What is atomicity?
3. What is consistency?
4. What is isolation?
5. What is durability?