PSR-6 Cache Introduction

In the late fall 2015 the PHP-FIG released a specification for caching. It is called PSR-6. Like all the PSRs, it is just a recommendation for improve interoperability.

Basic concepts

The PSR-6 defines two interfaces; a CachePool and a CacheItem. You interact with the pool to get an item. You will never create an item yourself.

// Create a pool
$pool = new ApcuCachePool();

// Get an item (existing or new)
$item = $pool->getItem('cache_key');

// Set some values and store

// Verify existence
$pool->hasItem('cache_key'); // True
$item->isHit(); // True

// Get stored values
$myValue = $item->get();
echo $myValue; // "value"

// Delete
$pool->hasItem('cache_key'); // False

Note: A cache item can not be transferred from one pool to another.

Cache keys

According to PSR-6 the following characters could be used in a valid cache key; A-Z, a-z, 0-9, _, and .. Some characters are forbidden like: {}()/\@:. If you use any of the forbidden characters you will get an exception. Other characters (like -) are not forbidden nor valid. It is up to the implementation if they support that character or not.

We recommend to always use valid characters in the cache key.

To make sure you do not use an invalid character by mistake, you should hash your keys.

$cacheKey = sha1($_SERVER['REQUEST_URI']);

Choosing a pool

What cache pool you want to use is up to you. As you can see in the table on the startpage, different pools have different features. Commonly used pools are:

  • Apcu
  • Array
  • Memcached
  • Redis

The steps to create a pool varies from pool to pool. Look at the pool's repository to see how to create it. Generally you create a connection to a cache implementation and then give it to the pool. See a Memcached example:

$client = new \Memcached();
$client->addServer('localhost', 11211);
$pool = new MemcachedCachePool($client);


The PHP-Cache organization has built some more features on top of PSR-6. Look at our documentation for hierarchy or namespace for more information.