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Advanced 20 min readModule: Module 10: Transactions, Isolation Levels & Row Locks

ACID Transactions, Row Locks & Isolation Levels

Ensure financial-grade data integrity with transactions, ROLLBACK on errors, and SELECT ... FOR UPDATE locks.

What You Will Learn in This Lesson

  • The 4 ACID Pillars: Atomicity, Consistency, Isolation, Durability
  • Transaction lifecycle: BEGIN, COMMIT, ROLLBACK
  • Pessimistic locking with SELECT ... FOR UPDATE to prevent race conditions

Introduction & Core Concept

A database transaction is a sequence of multiple database operations executed as a single, atomic unit of work. Either all statements succeed, or the entire batch rolls back completely.
WHY DOES THIS MATTER IN THE REAL WORLD?

In bank transfers, deducting from Account A and adding to Account B must be atomic. If the server crashes mid-way, money cannot vanish into thin air.

Atomic Bank Transfer Transaction

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BEGIN;
 
-- 1. Deduct from sender with row lock
UPDATE accounts 
SET balance = balance - 100 
WHERE id = 'acc_sender' AND balance >= 100;
 
-- 2. Credit to receiver
UPDATE accounts 
SET balance = balance + 100 
WHERE id = 'acc_receiver';
 
COMMIT; -- All mutations become permanent atomically

Line-by-Line Technical Breakdown

1Isolation levels (Read Committed, Repeatable Read, Serializable) balance concurrency with isolation.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[SQL]
SQL SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Keep transactions as short as possible to minimize row lock contention.

Lesson Summary & Core Takeaways

  • ACID transactions guarantee total consistency and crash resilience.