When we talk about WordPress caching, most people think of Page Caching (saving a static HTML copy of a page). But if your site has dynamic content—like an eCommerce store, a membership site, or a busy forum—page caching isn’t enough. You need Object Caching.
What is Object Caching?
WordPress relies heavily on its database. Every time a page loads, WordPress runs dozens (sometimes hundreds) of SQL queries to fetch options, post data, and user metadata.
Object Caching saves the results of these database queries in the server’s RAM. The next time WordPress needs that specific piece of data, it grabs it instantly from memory instead of querying the database again.
By default, WordPress has built-in object caching, but it is non-persistent. This means the cache is cleared at the end of every page load. To truly speed up your site, you need Persistent Object Caching.
Implementing Persistent Object Caching
To enable persistent object caching, your server must have specific software installed: usually Redis or Memcached.
Step 1: Check Server Compatibility
Contact your hosting provider and ask them to enable Redis or Memcached for your account. Most premium managed WordPress hosts (like Kinsta, WPEngine, or Cloudways) have this available with a single click in their dashboard.
Step 2: Install a Drop-In Plugin
Once enabled on the server, you need to tell WordPress to use it.
For Redis:
Install and activate the free plugin: Redis Object Cache.
Navigate to Settings > Redis and click “Enable Object Cache”.
For Memcached:
Install and activate the free plugin: Memcached Redux.
This plugin works by dropping an object-cache.php file into your /wp-content/ directory.
Troubleshooting Object Cache Issues
1. Admin Dashboard is Slow
Sometimes, aggressive object caching can make the backend dashboard slow or buggy. If this happens, you can disable object caching specifically for the admin area by adding this to wp-config.php:
define( 'WP_CACHE', false ); // Turns off standard cache(Note: Some specific drop-in plugins handle admin exclusion differently, check their documentation).
2. Changes Not Appearing on the Live Site
Because queries are cached in memory, changes you make (like updating a setting) might not appear immediately.
The Fix:
You need to flush the object cache. You can do this via the settings page of your Redis/Memcached plugin, or by using WP-CLI via SSH:
wp cache flushImplementing persistent object caching is the single most effective way to reduce database load and speed up dynamic WordPress websites.