Using Joomla 1.5 to cache expensive computations

Monday, 01 June 2009

Sometimes you need to preserve some computation results for a while, and have it refresh automatically. You may use this technique for periodic RSS fetching, or a really heavy SQL query. There are many more applications, of course.

Joomla's cache system allows you to automatically cache the output and result of a function(in this example the '_fetch' static method from the 'Currency' class). Cache's purpose is to offload your servers (and remote servers if fetching remote data), and speed up page display.

The $res will return the cached function result(if fresh enough). If the result is older than 'lifetime' seconds, the cache call will execute the function again, and store the result for another 'lifetime' seconds. In other words, the cache refreshes every 'lifetime' seconds.

Take note that the class is not instantiated, we're just using it for namespace purposes. The actual call will be the same as calling Currency::_fetch() from PHP.

The code below creates and uses a 'Currency' subfolder in Jomla's cache folder(if the cache system was configured for file storage in Joomla administration). To clear the cache, you may use Tools->Clean cache from Joomla administration.

// cache subfolder(group) 'Currency', cache method: callback
$cache= & JFactory::getCache('Currency','callback');
 
// save configured lifetime
 
@$lifetime=$cache->lifetime;
 
$cache->setLifeTime(86400/2); // check twice per day
 
// save cache conf
 
$conf =& JFactory::getConfig();
 
// check if cache is enabled in configuration
 
$cacheactive = $conf->getValue('config.caching');
 
$cache->setCaching(1); //enable caching
 
// Currency=classname, _fetch=static method. The $res will hold the cached return value
 
// if the cache expired, the method will be called again and the result will be stored for 'lifetime' seconds
 
$res = $cache->call(array('Currency','_fetch')); 
 
// revert configuration
 
$cache->setCaching($cacheactive);