What is the cache ?

Each time a web page is displayed Joomla! needs to fetch information from both the database (menu's, modules etc), the template dirctory (logo, graphics etc) and other components of Joomla!.

When you have a lot of users hitting your site simultaneously this can be quite a overhead so Joomla! has built in cache which can be enabled / disabled.

The cache is turned on by default and can be turned off via Site->Global Configuration->system tab->Cache settings.

When the cache is enabled Joomla! will store information in a temporary cache file. When the next request for that information is requested Joomla! will use the information from the cached page instead of retrieving information from all the original components. The downside to this is that those components that do not use the caching feature of Joomla! (not all third party components take advantage of this caching feature) may start displaying stale copies of the web page if you have made changes within the time period set within the Cache settings, which is set to 15 minutes by default. For the technically minded people out there ... Joomla! caches the actual return values from functions.

For example :-

• Caching is turned on
• Cachtime is 15 minutes (Every 15 minutes Joomla! will refresh the cached page from the database)
• 9:00 - Frontpage article is entitled 'Stale pages and Joomla cache'
• 9:01 - Visitor sees the article title 'Stale pages and Joomla cache'
• 9:10 - You modify the article title to ''Stale pages and Joomla! cache' (a ! is added to the word Joomla)
• 9:12 - Another Visitor sees the article title 'Stale pages and Joomla cache'(will see stale page as 15 minutes has not passed)
• 9:17 - Another Visitor sees the article title 'Stale pages and Joomla! cache' (Joomla refreshed the cache

The benefits of using the cache far outweigh having to manually clear the cache if you make changes to articles / module positions etc and want the changes to appear immediately.

Clearing the cache manually

• Tools->Clean Cache to display the Cache Manager - Clean Cache Admin page
• Check each box (or click the top box to select all boxes)
• Click Delete