An object cache is a server-side caching layer that stores the results of expensive WordPress database queries and PHP computations in fast memory — typically Redis or Memcached — so identical requests within subsequent page loads are served from the in-memory store rather than re-executing the database query. WordPress includes a built-in non-persistent object cache (WP_Object_Cache) that survives only for the duration of a single page request. For persistent object caching that carries results across multiple page loads, a memory store must be connected via a wp-content/object-cache.php drop-in. Redis Object Cache by Till Krüss is the most widely used drop-in. Managed WordPress hosts (WP Engine, Kinsta, Pressable) provide persistent Redis object caching by default. Object caching is particularly impactful on sites with repeated expensive queries: WooCommerce product lookups, membership permission checks, or news archives with complex taxonomy queries.
Glossary entry
