How to Configure Redis Object Cache for Wordpress to Reduce Database Load

ByAkensai

Learning how to configure Redis object cache for WordPress to reduce database load is one of the best performance upgrades you can make to a busy WordPress site. Every time a visitor loads a page, WordPress makes multiple database queries. On high-traffic sites, this creates serious bottlenecks. Redis stores the results of those queries in memory. This means WordPress retrieves data from RAM instead of hitting the database repeatedly. The result is faster page loads and a much lighter server. In this tutorial, you’ll install Redis on Ubuntu, connect it to WordPress using a plugin, and verify that caching is working correctly.

Prerequisites for Configuring Redis Object Cache for WordPress to Reduce Database Load

Before you start, make sure you have the following in place.

Server requirements:
– Ubuntu 20.04 or 22.04 (this guide uses Ubuntu)
– Root or sudo access via SSH
– WordPress installed and running
– Apache or Nginx as your web server
– PHP 7.4 or higher

Assumed knowledge:
– Basic Linux command-line usage
– Familiarity with WordPress admin dashboard
– Ability to edit files using nano or vim

Estimated time: 20–30 minutes

You don’t need prior Redis experience. This tutorial walks you through everything from installation to verification. If your WordPress site is hosted on a managed platform like WP Engine or Kinsta, Redis may already be available through their dashboard. Check with your host before proceeding.

How to Configure Redis Object Cache for WordPress to Reduce Database Load

Related article: How to Set Up Nginx Reverse Proxy with Ssl Termination Using Docker and Let’s Encrypt Certbot

Follow these steps carefully. Each step builds on the previous one.

Step 1: Update your server packages

Always start with a fresh package list. Run the following command:

sudo apt update && sudo apt upgrade -y

This ensures you install the latest available version of Redis.

Step 2: Install Redis on Ubuntu

Install the Redis server package with this command:

sudo apt install redis-server -y

Once installed, start and enable Redis so it runs on boot:

sudo systemctl start redis-server
sudo systemctl enable redis-server

Verify Redis is running:

sudo systemctl status redis-server

You should see active (running) in the output.

Step 3: Test the Redis connection

Run a quick test using the Redis CLI:

redis-cli ping

Redis should respond with PONG. If it does, your Redis server is working correctly.

Step 4: Install the PHP Redis extension

WordPress needs a PHP extension to communicate with Redis. Install it now:

sudo apt install php-redis -y

Restart your web server to load the extension. For Apache:

sudo systemctl restart apache2

For Nginx with PHP-FPM:

sudo systemctl restart php8.1-fpm

Replace php8.1-fpm with your actual PHP version.

Step 5: Install the Redis Object Cache plugin

Log in to your WordPress admin dashboard. Go to Plugins → Add New. Search for Redis Object Cache by Till Krüss. Install and activate it.

This plugin acts as the bridge between WordPress and your Redis server.

Step 6: Add Redis settings to wp-config.php

You need to tell WordPress where Redis is running. Open your wp-config.php file:

sudo nano /var/www/html/wp-config.php

Add these lines just above the line that says / That's all, stop editing! /:

define('WP_REDIS_HOST', '127.0.0.1');
define('WP_REDIS_PORT', 6379);
define('WP_REDIS_TIMEOUT', 1);
define('WP_REDIS_READ_TIMEOUT', 1);
define('WP_REDIS_DATABASE', 0);

Save the file with Ctrl+O, then exit with Ctrl+X.

Step 7: Enable the object cache from the plugin

Go back to your WordPress dashboard. Navigate to Settings → Redis. You’ll see the connection status. Click Enable Object Cache. The plugin creates a object-cache.php drop-in file inside your wp-content folder. This file intercepts WordPress database calls and routes them through Redis.

Step 8: Verify Redis is caching data

Check Redis is receiving data by running this command on your server:

redis-cli monitor

Reload a page on your WordPress site. You should see Redis commands appearing in the terminal output. Press Ctrl+C to stop the monitor.

You can also check how many keys Redis has stored:

redis-cli dbsize

A number greater than zero confirms WordPress is writing to Redis.

Troubleshooting Redis Object Cache Issues in WordPress

Even a clean setup can hit snags. Here are the most common problems and how to fix them.

Problem: Status shows “Not connected” in the plugin dashboard

Check that the PHP Redis extension loaded correctly:

php -m | grep redis

If nothing appears, the extension isn’t active. Re-run sudo apt install php-redis -y and restart your web server.

Problem: Redis is running but WordPress isn’t caching

Double-check your wp-config.php values. A typo in the host or port will break the connection. Also confirm the object-cache.php file exists:

ls /var/www/html/wp-content/object-cache.php

If the file is missing, disable and re-enable the plugin from the dashboard.

Problem: Redis runs out of memory

By default, Redis has no memory limit. Set one to prevent it from consuming all available RAM. Edit the Redis config:

sudo nano /etc/redis/redis.conf

Find and update these lines:

maxmemory 256mb
maxmemory-policy allkeys-lru

The allkeys-lru policy removes the least recently used keys when memory fills up. Restart Redis after saving:

sudo systemctl restart redis-server

Problem: Cache not clearing after content updates

The Redis Object Cache plugin handles cache invalidation automatically. If you’re seeing stale content, try flushing the cache manually from Settings → Redis → Flush Cache.

For more details on Redis configuration options, check the official Redis configuration documentation.

Conclusion

You now know how to configure Redis object cache for WordPress to reduce database load on your server. You installed Redis, connected it to WordPress through the Redis Object Cache plugin, and confirmed that caching is active. Your site now stores database query results in memory. This cuts response times and takes pressure off your MySQL server. The more traffic your site gets, the bigger the performance difference you’ll notice. From here, you can explore adding a full-page cache with a plugin like W3 Total Cache, or look into setting up Redis with a password for added security. Small server-side changes like this one make a real difference as your WordPress site grows.

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