Simple definition
The WordPress object cache stores results of database queries and other reusable application data.
Technical definition
The default WordPress object cache lasts for one request. A persistent object cache drop-in, often backed by Redis or Memcached, can reuse cached objects across requests. Cache invalidation remains essential after updates.
What is it used for?
Reduce repeated database work and improve response times on query-heavy WordPress sites.
Practical example
On a busy WooCommerce site, a compatible Redis object cache can reduce repeated database lookups; measure performance and avoid caching data that must remain fresh.
Common issues
- Plugin or theme conflict
- Incompatible update
- Cache hiding the change