Caching

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# Chapter 13. Caching

Caching is used to speed up a call to display() or fetch() by saving its output to a file. If a cached version of the call is available, that is displayed instead of regenerating the output. Caching can speed things up tremendously, especially templates with longer computation times. Since the output of display() or fetch() is cached, one cache file could conceivably be made up of several template files, config files, etc.

Since templates are dynamic, it is important to be careful what you are caching and for how long. For instance, if you are displaying the front page of your website that does not change its content very often, it might work well to cache this page for an hour or more. On the other hand, if you are displaying a page with a weather map containing new information by the minute, it would not make sense to cache this page.

# Setting Up Caching

The first thing to do is enable caching. This is done by setting $caching = true (or 1.)

Example 13-1. enabling caching
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = true; $smarty->display('index.tpl'); ?>`

With caching enabled, the function call to display('index.tpl') will render the template as usual, but also saves a copy of its output to a file (a cached copy) in the $cache_dir. Upon the next call to display('index.tpl'), the cached copy will be used instead of rendering the template again.

> Technical Note: The files in the $cache_dir are named similar to the template name. Although they end in the ".php" extention, they are not really executable php scripts. Do not edit these files!

Each cached page has a limited lifetime determined by $cache_lifetime. The default value is 3600 seconds, or 1 hour. After that time expires, the cache is regenerated. It is possible to give individual caches their own expiration time by setting $caching = 2. See the documentation on $cache_lifetime for details.

Example 13-2. setting cache_lifetime per cache
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = 2; // lifetime is per cache // set the cache_lifetime for index.tpl to 5 minutes $smarty->cache_lifetime = 300; $smarty->display('index.tpl'); // set the cache_lifetime for home.tpl to 1 hour $smarty->cache_lifetime = 3600; $smarty->display('home.tpl'); // NOTE: the following $cache_lifetime setting will not work when $caching = 2. // The cache lifetime for home.tpl has already been set // to 1 hour, and will no longer respect the value of $cache_lifetime. // The home.tpl cache will still expire after 1 hour. $smarty->cache_lifetime = 30; // 30 seconds $smarty->display('home.tpl'); ?>`

If $compile_check is enabled, every template file and config file that is involved with the cache file is checked for modification. If any of the files have been modified since the cache was generated, the cache is immediately regenerated. This is a slight overhead so for optimum performance, leave $compile_check set to false.

Example 13-3. enabling $compile_check
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = true; $smarty->compile_check = true; $smarty->display('index.tpl'); ?>`

If $force_compile is enabled, the cache files will always be regenerated. This effectively turns off caching. $force_compile is usually for debugging purposes only, a more efficient way of disabling caching is to set $caching = false (or 0.)

The is_cached() function can be used to test if a template has a valid cache or not. If you have a cached template that requires something like a database fetch, you can use this to skip that process.

Example 13-4. using is_cached()
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = true; if(!$smarty->is_cached('index.tpl')) { // No cache available, do variable assignments here. $contents = get_database_contents(); $smarty->assign($contents); } $smarty->display('index.tpl'); ?>`

You can keep parts of a page dynamic with the insert template function. Let's say the whole page can be cached except for a banner that is displayed down the right side of the page. By using an insert function for the banner, you can keep this element dynamic within the cached content. See the documentation on insert for details and examples.

You can clear all the cache files with the clear_all_cache() function, or individual cache files (or groups) with the clear_cache() function.

Example 13-5. clearing the cache
`<?php require('Smarty.class.php'); $smarty = new Smarty; $smarty->caching = true; // clear out all cache files $smarty->clear_all_cache(); // clear only cache for index.tpl $smarty->clear_cache('index.tpl'); $smarty->display('index.tpl'); ?>`

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