Setting the cache function in Joomla! to Yes is just the first step towards getting a better performing web site. You have to open the Global Configuration panel and go to the System tab. On the left side of the screen you can change the settings for the Cache Time. Cache Time is the time taken for a cached page to be regenerated after somebody opens the page. The page is stored in a special directory to be shown to a new visitor who wants to look at the page. This reduces the number of queries to the database, which will improve the loading time.
How you set the time for the cache depends on what kind of site you run. A news site needs to have a shorter cache time than a web site on which there are only a few updates per month. For the first case you can set it to around five minutes, and for the later you can easily go for several hours. You can clear the cache to show your content immediately after writing by using your Administrator panel (Tools | Clean Cache). You can do that only if you have minimal administrator rights at the backend.
If you have set the caching option, you still need to check the modules you use on your site. If you have a module that shows updates or changes according to the page that is visited, you should deactivate the function of module caching.
A standard Caching module will be set to Use Global, which means if the cache is on then the module content will be cached as well. If you have a module such as Related Articles, you need to change this and set it to No Caching as every page has different related items. Using cache on such a module will prevent the system from showing the real related pages.
You can also optimize some server settings that can affect the loading time of your site. To change the settings, go to the Server tab in Global Configuration.
The first option is to set the GZIP Page Compression to Yes, in order to reduce the file size of the downloads. If you set this option, make sure to check your site for the next couple of days. In some cases the GZIP compression will effectively stop your site from showing its pages. You might even find that your hosting provider does not allow the use of GZIP because it uses more CPU time.
The standard cache function may prevent you from seeing the problems that may occur. Therefore, it is important to check the site until you are sure it is running fine. The second option to change is to set Error Reporting to None. This ensures that any errors that may occur are not written to the database, reducing the number of write actions to the database and also keeping it smaller in size.
You can move your caching and do it outside your Joomla! installation. At joomlatwork.com they have a separate component that makes your Joomla! web site much faster.
The component takes the generated pages and puts them in a separate cache, so it's not the same cache as Joomla! uses. After the component has done its work, surfing your web site is like looking through static HTML files (to be honest, it's even faster).
This component is tested on a huge Dutch web site called www.kika.nl, which is about helping cancer-prone children. If you browse through this site, you will see how fast it performs. Although the site is built on Mambo, the page loading time is very short. The caching engine was completely rebuilt for Mambo 4.6 and Joomla 1.5. If you use it, it should bring the same benefits to your site. You can find more information at http://www.joomlatwork.com/products/components/joomla-performance.html.
There is also a downside to this component—it alters the index.php file from your Joomla! installation. If you use other components that do the same, you will run into trouble. You will need to check if everything still works after a Joomla! core version upgrade.