Atomic operations with Lua in Redis - Mini Project: Build & Apply

Atomic Operations with Lua in Redis

📖 Scenario: You are managing a Redis database for a simple online store. You want to safely update the stock count of a product without interference from other operations.

🎯 Goal: Build a Lua script that atomically checks the stock of a product and decreases it by a specified amount only if enough stock is available.

📋 What You'll Learn

Create a Redis key with the initial stock count for a product.

Define a variable for the amount to decrease the stock.

Write a Lua script that atomically checks if the stock is sufficient and decreases it.

Add the final command to execute the Lua script using Redis EVAL.

💡 Why This Matters

🌍 Real World

Managing stock counts in an online store requires atomic updates to prevent overselling.

💼 Career

Understanding Lua scripting in Redis is valuable for backend developers working with caching and real-time data stores.

1

DATA SETUP: Create a Redis key for product stock

Create a Redis key called product_stock and set its value to 100 to represent the initial stock count.

Redis

# Your code here to set product_stock to 100

Need a hint?

Use the Redis SET command to create the key and assign the value.

2

CONFIGURATION: Define the amount to decrease stock

Define a Lua variable called decrease_amount and set it to 5 to represent how many items to remove from stock.

Redis

SET product_stock 100
-- Define decrease_amount variable in Lua
-- Your code here

Need a hint?

Use local decrease_amount = 5 to define the variable inside the Lua script.

3

CORE LOGIC: Write Lua script for atomic stock decrease

Write a Lua script that uses redis.call('GET', 'product_stock') to get the current stock, converts it to a number, checks if it is greater or equal to decrease_amount, and if yes, decreases the stock by decrease_amount using redis.call('SET', 'product_stock', new_stock). Use variables current_stock and new_stock.

Redis

SET product_stock 100
local decrease_amount = 5
-- Your Lua script here to atomically decrease stock

Need a hint?

Use tonumber to convert the stock string to a number. Use if to check stock and redis.call('SET', ...) to update.

4

COMPLETION: Execute the Lua script atomically with Redis EVAL

Write the Redis EVAL command to run the Lua script atomically. Use the full Lua script as a string, pass 0 for the number of keys, and no additional arguments.

Redis

SET product_stock 100
local decrease_amount = 5
local current_stock = tonumber(redis.call('GET', 'product_stock'))
if current_stock >= decrease_amount then
    local new_stock = current_stock - decrease_amount
    redis.call('SET', 'product_stock', new_stock)
end
-- Your EVAL command here

Need a hint?

Use EVAL with the Lua script as a string and 0 keys to run the script atomically.