Joomla caching, in the order you should turn it on

Caching in Joomla is not one setting. Knowing which layer does what saves you from the classic outcome, where the site is faster and also subtly wrong.

The layers

View cache stores component output, so the article view does not rebuild its query on every hit. This is the System Cache setting in Global Configuration, on the System tab.

Module cache stores each module's output separately. It is controlled per module, in its Advanced tab, and honours the global cache time unless you override it.

Page cache stores the entire rendered page and serves it without running most of Joomla at all. That is the System - Page Cache plugin, and it is the one that makes the biggest difference and causes the most trouble.

The order

Start with System Cache set to Conservative, cache handler File, cache time somewhere between 15 and 60 minutes depending on how often your content changes. Test the site. Log in, log out, submit a form.

Then enable module caching where it clearly helps: menus, banners, anything listing articles. Leave login and cart modules alone.

Only then consider Page Cache, and only if the site is genuinely mostly anonymous visitors reading the same pages. Read its options before enabling it: it has settings for excluding menu items and for whether it caches for logged-in users. Get those wrong on a site with a members area and you will hand one member another member's page.

Clearing it

System, Clear Cache in the admin, or from the command line:

php cli/joomla.php cache:clean

Put that in your deployment routine. Half the "the change did not go live" reports are a cache that was never cleared.

What caching will not fix

If a page takes four seconds because a module runs an unindexed query across 40.000 rows, caching hides it from most visitors and leaves it just as slow for the unlucky one who triggers the rebuild. Find the slow thing first. Cache afterwards, to save the work you have already made cheap.