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

ByAkensai

Learning how to configure Redis object cache in WordPress to reduce database load is one of the best performance upgrades you can make for a high-traffic site. Every time a visitor loads a WordPress page, PHP queries the database repeatedly. This gets expensive fast. Redis stores those query results in memory. WordPress retrieves them instantly on the next request. The result is fewer database queries, faster page loads, and a server that handles traffic spikes much more gracefully. In this tutorial, you’ll install Redis on your Linux server, connect it to WordPress using the Redis Object Cache plugin, and verify everything works correctly. By the end, your site will be hitting the database far less often.

Prerequisites to Configure Redis Object Cache in WordPress

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

Server access: You need SSH access to your Linux server with sudo privileges. This tutorial assumes Ubuntu 20.04 or 22.04.

WordPress installation: A working WordPress site with admin access. You should be able to install plugins.

Basic Linux knowledge: You should be comfortable running commands in a terminal.

Estimated time: About 20–30 minutes from start to finish.

Software versions this tutorial uses:
– Ubuntu 20.04 / 22.04
– Redis 6.x or 7.x
– PHP 7.4 or higher with the php-redis extension
– WordPress 5.x or 6.x

You also need the Redis Object Cache plugin by Till Krüss from the WordPress plugin repository. It’s free and actively maintained.

Check your PHP version before proceeding:

php -v

Make sure it returns PHP 7.4 or higher. If you’re running an older version, upgrade PHP first.

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

This event shares similarities with: How to Install and Configure Fail2ban on Ubuntu to Protect Against Brute-force Attacks

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

Step 1: Install Redis on your server

Connect to your server via SSH. Run the following commands to install Redis:

sudo apt update
sudo apt install redis-server -y

Once installed, start Redis and enable it to run 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 2: Install the PHP Redis extension

WordPress needs the PHP Redis extension to communicate with the Redis server. Install it with:

sudo apt install php-redis -y

Restart your web server to load the extension. Use the command that matches your setup:

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-FPM version.

Confirm the extension loaded:

php -m | grep redis

This should return redis.

Step 3: Configure Redis for WordPress

Open the Redis configuration file:

sudo nano /etc/redis/redis.conf

Find the maxmemory line and set a limit. This prevents Redis from consuming all available RAM:

maxmemory 256mb
maxmemory-policy allkeys-lru

The allkeys-lru policy tells Redis to evict the least recently used keys when memory fills up. This is the right choice for a WordPress object cache.

Save the file and restart Redis:

sudo systemctl restart redis-server

Step 4: Install the Redis Object Cache plugin

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

Step 5: Add Redis settings to wp-config.php

Open your wp-config.php file. Add these lines above the / That's all, stop editing! / line:

define('WP_REDIS_HOST', '127.0.0.1');
define('WP_REDIS_PORT', 6379);
define('WP_REDIS_DATABASE', 0);
define('WP_REDIS_TIMEOUT', 1);
define('WP_REDIS_READ_TIMEOUT', 1);
define('WP_REDIS_MAXTTL', 86400);

Save the file. These settings tell WordPress where to find your Redis server.

Step 6: Enable the object cache

Go to Settings → Redis in your WordPress dashboard. You’ll see the Redis connection status. Click Enable Object Cache. The plugin creates a object-cache.php drop-in file in your wp-content directory.

The status should change to Connected. You’ll also see a hit/miss ratio once traffic starts flowing.

Step 7: Verify Redis is caching data

Run this command to open the Redis CLI:

redis-cli

Then check the number of keys stored:

DBSIZE

Browse a few pages on your WordPress site. Run DBSIZE again. The number should increase. This confirms WordPress is writing data to Redis.

You can also monitor live activity:

redis-cli MONITOR

Press Ctrl+C to stop monitoring.

Troubleshooting Redis Object Cache Issues in WordPress

Here are the most common problems and how to fix them.

Problem: Plugin shows “Not Connected”

Check that Redis is actually running:

sudo systemctl status redis-server

Also confirm the host and port in wp-config.php match your Redis config. By default, Redis listens on 127.0.0.1:6379.

Problem: php-redis extension not found

Run php -m | grep redis. If nothing returns, reinstall the extension:

sudo apt install --reinstall php-redis -y
sudo systemctl restart apache2

Problem: Redis runs out of memory

If Redis evicts keys too aggressively, increase the maxmemory value in /etc/redis/redis.conf. A good starting point is 512mb for busier sites.

Problem: object-cache.php file missing

The plugin creates this file automatically. If it’s missing, deactivate and reactivate the plugin. You can also check file permissions on your wp-content directory:

ls -la /var/www/html/wp-content/

The web server user (usually www-data) needs write access.

Tip: If you run multiple WordPress sites on one server, use a different Redis database number for each. Set WP_REDIS_DATABASE to 1, 2, etc. for each site. This keeps their cached data separate.

For deeper performance analysis, consider pairing Redis with a full-page cache plugin like W3 Total Cache. Object caching and page caching work well together.

Conclusion

You now know how to configure Redis object cache in WordPress to reduce database load on your server. You installed Redis, connected it to WordPress, and verified the cache is working. Your site now stores database query results in memory. Repeated requests skip the database entirely. This makes a real difference under heavy traffic. Keep an eye on your Redis memory usage over the first few days. Adjust the maxmemory setting if needed. From here, you might explore persistent object caching strategies or look into Redis Sentinel for high-availability setups. Either way, knowing how to configure Redis object cache in WordPress to reduce database load gives you a solid foundation for scaling WordPress performance.

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