How to Tell if Query Caching is Enabled in CodeIgniter

CodeIgniter’s query caching functionality is great - once you’ve got your head around having to manually clear the caches when the database gets updated it works pretty much transparently, as a good cache should.

One annoying thing though is that there’s no documented way to tell if caching is enabled or not. Not a big problem most of the time, but occasionally it could be very handy indeed - for example, if you wanted to display some kind of “system status” panel, or maybe display a manual “clear cache” button in case something goes skewiff and you need to clear the cache.

The Answer

Having failed to find anything in the documentation or via a quick search, I decided to do what all good developers would and RTFS. Sure enough, there is a way of telling if query caching is enabled, as shown in this snippet from system/database/DB_driver.php shows:

// Is query caching enabled?  If the query is a "read type" 		
// we will load the caching class and return the previously 		
// cached query if it exists 		
if ($this->cache_on == TRUE AND stristr($sql, 'SELECT')) 		
{ 			
	if ($this->_cache_init()) 			
	{ 				
		$this->load_rdriver(); 				
		if (FALSE !== ($cache = $this->CACHE->read($sql))) 				
		{ 					
			return $cache; 				
		} 			
	} 
}

The key part of that snippet is in the very first line of code - if($this->cache_on == TRUE… - this is how CodeIgniter checks internally whether query caching is enabled. $this->cache_on is set to TRUE or FALSE accordingly when you run the $this->db->cache_on() and $this->db->cache_off() methods.

So, if you want to tell whether query caching is enabled, you just have to check the value of $this->db->cache_on.

Be Careful!

All well and good, but using the internal variable like this can be dangerous. $this->db->cache_on looks an awful lot like $this->db->cache_on() but they can have very different results. It would be best to have a getter that would just return the state of $this->db->cache_on, but because you can’t extend the database classes it’s not as simple as it would usually be in CodeIgniter.

I have submitted a ticket to the CodeIgniter Reactor forum - if you agree that a getter would be useful, cast your votes and we’ll see if we can get it included in a future release!

Main image: “Hard Disk” by fDhooghe

Tags: Caching CodeIgniter Databases Optimization PHP

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