OpCache Adapter (PSR-16 )

A PSR-16 Simple Cache Implementation.

Out-of-the-Box Bytecode Cache

PHP is an interpreted language. The default PHP runtime compiles PHP sourcecode to an intermediate representation called PHP bytecode which is then executed. A bytecode cache stores this compiled representation of PHP sourcecode in shared memory. This eliminates the need to load and compile sourcecode on each request which leads to a significant increase in performance (up to 70% more requests per second).

The basic idea, when executing a PHP script is in two steps:

• First: the PHP code, written in plain-text, is compiled to opcodes
• Then: those opcodes are executed.

When you have one PHP script, as long as it is not modified, the opcodes will always be the same ; so, doing the compilation phase each time that script is to be executed is kind of a waste of CPU-time.

To prevent that redundant-compilation, there are some opcode caching mechanism that you can use.

Once the PHP script has been compiled to opcodes, those will be kept in RAM -- and directly used from memory the next time the script is to be executed ; preventing the compilation from being done again and again.

Read more

• https://blog.graphiq.com/500x-faster-caching-than-redis-memcache-apc-in-php-hhvm-dcd26e8447ad#.tsokdw9d4
• https://github.com/TerryE/opcache/wiki/The-Zend-Engine-and-opcode-caching#opcode-caching-with-opcache
• https://juokaz.com/blog/from-php-to-machine-code

Installation

composer require odan/cache

Usage

$cachePath = sys_get_temp_dir() . '/cache';

$cache = new \Odan\Cache\Simple\OpCache($cachePath);

// set a opcache value
$cache->set('foo', 'bar');

// get a opcache value
echo $cache->get('foo'); // bar

Known issues

Fatal error: Call to undefined method stdClass::__set_state()

If there are objects in the value, they will be written as stdClass::__set_state(). This is fine for objects where __set_state() can be added, but it can't be added to stdClass.

To fix this issue just serialize the value you are trying to cache:

$cache->set('key', serialize($object));

Then unserialize the string back to the original value:

$object = unserialize($cache->get('key'));

Race conditions

If you're in a high-concurrency environment you should avoid using a filesystem cache. Multiple operations on the file system are very hard to make atomic in PHP.

Alternative OPcache implementations

• laminas/laminas-cache - See the Filesystem Adapter
• Symonfy Php Files Cache Adapter