EVAL command for Lua execution in Redis - Mini Project: Build & Apply

Using the EVAL Command for Lua Execution in Redis

📖 Scenario: You are managing a Redis database for a small online store. You want to use Lua scripting to perform atomic operations that combine multiple Redis commands into one.

🎯 Goal: Learn how to write and execute a simple Lua script using the Redis EVAL command to increment a product's stock count safely.

📋 What You'll Learn

Create a Redis key for a product stock count with an initial value

Write a Lua script that increments the stock count by a given amount

Use the EVAL command to run the Lua script with keys and arguments

Verify the stock count is updated correctly after script execution

💡 Why This Matters

🌍 Real World

Using Lua scripts with Redis EVAL allows atomic operations that combine multiple commands, useful in inventory management, counters, and session handling.

💼 Career

Many backend developers and database administrators use Redis scripting to ensure data consistency and improve performance in real-time applications.

1

DATA SETUP: Create a Redis key for product stock

Use the Redis command SET to create a key called product_stock with the initial value 10.

Redis

# Your Redis command here
# Use SET product_stock 10

Need a hint?

Use the SET command to assign the value 10 to the key product_stock.

2

CONFIGURATION: Write a Lua script to increment stock

Create a Lua script string called increment_script that increments the key's value by the first argument ARGV[1]. Use redis.call('INCRBY', KEYS[1], ARGV[1]) inside the script.

Redis

SET product_stock 10
-- Define Lua script to increment stock
-- Your code here

Need a hint?

Assign the Lua script as a string to increment_script. It should call INCRBY on KEYS[1] with ARGV[1] converted to a number.

3

CORE LOGIC: Use EVAL to run the Lua script

Use the Redis EVAL command to run the increment_script with 1 key, the key name product_stock, and the increment value 5 as argument. The command format is EVAL increment_script 1 product_stock 5.

Redis

SET product_stock 10
local increment_script = "return redis.call('INCRBY', KEYS[1], tonumber(ARGV[1]))"
-- Run EVAL command to increment stock by 5
-- Your code here

Need a hint?

Use the EVAL command with the script variable, number of keys 1, the key product_stock, and the increment 5.

4

COMPLETION: Verify the updated stock count

Use the Redis GET command to check the value of product_stock after running the script. The command is GET product_stock.

Redis

SET product_stock 10
local increment_script = "return redis.call('INCRBY', KEYS[1], tonumber(ARGV[1]))"
EVAL increment_script 1 product_stock 5
# Your Redis command here to get updated stock

Need a hint?

Use GET product_stock to see the new stock value after increment.