Transactions vs Lua scripts in Redis - Hands-On Comparison

Understanding Transactions vs Lua Scripts in Redis

📖 Scenario: You are managing a Redis database for a simple online store. You want to update the stock quantity of a product safely when a purchase happens. You will learn how to do this using Redis transactions and Lua scripts.

🎯 Goal: Build two Redis commands: one using a transaction with MULTI and EXEC, and another using a Lua script to update product stock atomically.

📋 What You'll Learn

Create a Redis key product:1001:stock with initial stock value 10

Use a Redis transaction to decrement stock by 1 safely

Write a Lua script to decrement stock by 1 atomically

Ensure the stock does not go below zero in both methods

💡 Why This Matters

🌍 Real World

Managing inventory stock safely in an online store to prevent overselling.

💼 Career

Understanding Redis transactions and Lua scripting is essential for backend developers working with Redis to ensure data consistency and atomic operations.

1

DATA SETUP: Create the initial stock key

Create a Redis key called product:1001:stock and set its value to 10 using the SET command.

Redis

# Your Redis command here to set initial stock

Need a hint?

Use the SET command with the key product:1001:stock and value 10.

2

CONFIGURATION: Start a transaction to decrement stock

Start a Redis transaction using the MULTI command to prepare for decrementing the stock.

Redis

SET product:1001:stock 10
# Start transaction with MULTI

Need a hint?

Use the MULTI command to start a transaction block.

3

CORE LOGIC: Decrement stock safely inside the transaction

Within the transaction, use the DECRBY command on product:1001:stock to decrement the stock by 1. Then use EXEC to execute the transaction.

Redis

SET product:1001:stock 10
MULTI
# Decrement stock by 1
# Execute transaction

Need a hint?

Use DECRBY product:1001:stock 1 inside the transaction, then EXEC to run it.

4

COMPLETION: Write a Lua script to decrement stock atomically

Write a Lua script that checks if product:1001:stock is greater than 0, then decrements it by 1 and returns the new stock. Use the EVAL command with this script.

Redis

SET product:1001:stock 10
MULTI
DECRBY product:1001:stock 1
EXEC
# Write Lua script with EVAL to decrement stock atomically

Need a hint?

Use EVAL with a Lua script that gets the stock, checks if it's above zero, decrements it, and returns the new value.