Part 121: ACID Properties Explained: Atomicity, Consistency, Isolation & Durability

The ACID model is the gold standard for transactional database reliability.

1. The Four ACID Guarantees

A: Atomicity ("All or Nothing")

A transaction is treated as a single indivisible unit of work. If a money transfer deducts from Account A and adds to Account B, either both steps succeed, or if a crash occurs midway, neither occurs.

C: Consistency ("Rules are Never Broken")

A transaction can only bring the database from one valid state to another. All constraints, primary keys, foreign keys, and check rules must remain intact.

I: Isolation ("Concurrent Transactions Don't Interfere")

Concurrent transactions execute as if they were running serially one after another, preventing phantom reads and intermediate state leakage.

D: Durability ("Committed Data is Permanent")

Once a transaction commits, its changes survive power outages, crashes, or reboots through persistent Write-Ahead Logs (WAL).

Key Takeaways

• ACID guarantees that business-critical data remains correct and permanent in all circumstances.

In Part 122, we master Transaction Control Commands: BEGIN, COMMIT & ROLLBACK!