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Caching with PHP5

Question: Whats the best way to improve performance of your website?
Answer: Get rid of it, and stop worrying.

Unfortunately, that's not always practical (livelihoods etc). So lets have a look at caching instead. Rather miraculously I've just written and published some nifty caching code.

The code is PHP5 only, and built with a static class mindset. This kinda uses the OOP system as namespaces, though also uses inheritance to reuse common code. The code is separated out into three classes, Cache, OutputCache and DataCache. Groups and unique IDs are used to identify individual cached content. This comes in handy if you have to clear just a certain section of the cached data.

The Cache class is the base class, and contains common code for generating filenames, and reading and writing data files. Most of the code here is protected, as you shouldn't be interfacing with this class directly except in one instance, which is enabling or disabling the cache.
Output Cache

The OutputCache class is used for caching the generated output of your scripts, or certain sections of them. It has Start and End methods, and is used like this:

if (!OutputCache::Start("myGroup", "myID", 600)) {

// Generate some output (as you do)...



So whats happening here? Well first off the call to Start() passes the group, unique ID and the TTL (Time To Live) for this particular bit of caching. So the data will be uniquely identified on disk by the group/id combo, and will be considered stale after the TTL number of seconds have passed. This function returns true if the data is found in the cache, and also prints the data to the screen. This means the code inside the if() block is skipped (thanks to the not (!) operator), and so the data isn't printed twice.

If however, the given combo of group/id isn't found in the cache, the Start() method will return false. When this happens output buffering is turned on to record the output. The code inside the if() block will then run (again - the not (!) operator), generate the output (which gets buffered), and then call the End() method. This method stops output buffering, saves the data to disk, and then prints it.

Elegant, efficient, and sexy. What more could you ask for?
Data Cache

The DataCache is used to cache data structures, as opposed to script output. This allows you to cache the creation of large arrays for example, or the results of slow queries. This is helpful if your pages are rather dynamic, though some areas aren't. Or in a recently experienced situation of mine: You have one central DB server, and multiple front end webservers. A common setup. If the load is getting high on the database, you might want to move some portion of queries (ORDER BY RAND() is a good example) to the webservers instead of the database server. Thus randomisation (eg using shuffle()) happens on one of 5 webservers, instead of your single resource limited database server. Anyway, some code:

if (!$data = DataCache::Get("myGroup", "myOtherID")) {

$result = $db->query("SELECT BIG_ASS_QUERY()");

DataCache::Put("myGroup", "myOtherID", 600, $result);

// Do something useful with $result


So in this example (very similar to output caching), if the data is cached, it's assigned to $data and the if() block is skipped. If not, then the if() block is run, and the data is cached at the Put() method call.
Miscellaneous Bits

There's a few configuration bits and bobs you can twiddle with if you like twiddling. setPrefix() as you can well imagine sets the prefix used in the cache data filenames. This defaults to "cache_". setStore() sets where the data files themselves are stored. This defaults to "/dev/shm/", since this is a convenient way to store the data files in shared memory. If you don't have this, try changing the path to "/tmp/". Must be given with a trailing slash.

And last, and least (so as not to be a corny ass), there's the static variable Cache::$enabled. That's how your refer to static class variables in case you didn't know. This is a boolean which enables or disables the cache. Surprising that.

C'est tout. Get the code here.


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