How WordPress Caching Works: From PHP Request to Cached HTML
A plain-English explanation of dynamic WordPress requests, cache hits, cache misses and invalidation.
Short answer: Without a full-page cache, a WordPress request can invoke PHP, query the database and assemble a response before the browser receives HTML. A page cache stores a reusable result so later eligible requests can skip much of that repeated work.
Caching is not a permanent snapshot. Good systems clear or regenerate cached content when relevant content changes.
What happens on an uncached request
Caching is not a permanent snapshot. Good systems clear or regenerate cached content when relevant content changes.
Query strings, cookies, authentication and ecommerce state can change whether a response is safe to cache.
- Identify which layer is caching the response.
- Prefer the narrowest safe purge instead of clearing every cache by default.
- Verify behavior while logged out or in a private browsing session when testing public page caching.
What becomes the cache key
Query strings, cookies, authentication and ecommerce state can change whether a response is safe to cache.
Measure both time to first byte and browser rendering because page caching addresses only part of the end-to-end experience.
- Identify which layer is caching the response.
- Prefer the narrowest safe purge instead of clearing every cache by default.
- Verify behavior while logged out or in a private browsing session when testing public page caching.
Cache hit versus miss
Measure both time to first byte and browser rendering because page caching addresses only part of the end-to-end experience.
Caching is not a permanent snapshot. Good systems clear or regenerate cached content when relevant content changes.
- Identify which layer is caching the response.
- Prefer the narrowest safe purge instead of clearing every cache by default.
- Verify behavior while logged out or in a private browsing session when testing public page caching.
When content is purged
Caching is not a permanent snapshot. Good systems clear or regenerate cached content when relevant content changes.
Query strings, cookies, authentication and ecommerce state can change whether a response is safe to cache.
- Change one important variable at a time.
- Compare repeatable behavior rather than one isolated score.
- Keep reliability and maintainability ahead of marginal benchmark gains.
Why logged-in users can behave differently
Query strings, cookies, authentication and ecommerce state can change whether a response is safe to cache.
Measure both time to first byte and browser rendering because page caching addresses only part of the end-to-end experience.
- Change one important variable at a time.
- Compare repeatable behavior rather than one isolated score.
- Keep reliability and maintainability ahead of marginal benchmark gains.
Practical decision rule
Fix the layer the evidence points to. Caching helps repeated server work; CSS and JavaScript work affect rendering and responsiveness; images and fonts affect transfer and discovery; hosting and application behavior affect origin response. Avoid solving a different problem just because a tool is popular.
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