Joomla System Cache vs Page Cache: What Is the Difference?
System Cache and Page Cache are separate controls
Joomla's Global Configuration → System → System Cache setting controls Conservative or Progressive caching. Page Cache is enabled through the separate System - Page Cache plugin. You can therefore configure these mechanisms independently; turning System Cache off does not by itself disable an enabled Page Cache plugin.
System Cache can reuse component and module output
Conservative and Progressive System Cache work below the full-page level. Eligible component views can be cached, while module handling depends on the selected mode. Conservative mode allows supported modules to opt in through Use Global or opt out with No caching; Progressive mode caches the page's modules together.
Page Cache stores the whole generated page
With System - Page Cache enabled, Joomla stores the full HTML for an eligible guest page and can serve that cached HTML on a later request to the same URL. Because Joomla can bypass normal page generation, Page Cache is the more aggressive option and requires particular care on interactive or personalized pages.
Their invalidation behavior can differ
Joomla components can clear related component or module cache groups when administrators modify content. Current Joomla Programmer Documentation warns that editing an article does not automatically clear the full Page Cache for every page on which it appears. That cached page can remain until expiry or an administrator clears it.
Page Cache has page-level exclusions
The System - Page Cache plugin provides parameters to exclude specified menu items and URLs. This is important for dynamic workflows such as carts, account interactions, or other pages where the same URL can produce state-dependent output. System Cache uses different component and module caching rules rather than those Page Cache exclusions.
Both should be tested as a guest
Joomla's current Programmer Documentation states that Page Cache, Progressive Caching, and Conservative Caching do not cache for logged-on users. An Administrator who tests only while authenticated can therefore miss cache behavior that affects public visitors.
Use the least aggressive mechanism that meets the goal
Start with a clear performance problem and measure the result of each change. Conservative System Cache provides finer module control; Progressive System Cache is less selective; Page Cache can provide the greatest reuse for truly static guest pages. Correctness, exclusions, and predictable content freshness matter more than simply enabling every cache layer.
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