OPcache

OPcache is a PHP extension that caches the compiled bytecode of PHP scripts, allowing PHP applications to skip the parsing and compilation phase on subsequent requests. By storing opcodes in shared memory, OPcache reduces CPU usage and improves response times, especially for high-traffic sites. It also supports preloading, which can initialize commonly used scripts at server startup, and invalidation rules that refresh the cache when source files change or after a configured interval.

OPcache originated as Zend OPcache, developed by Zend Technologies. It was integrated into the PHP project in PHP 5.5 and is now maintained as an official component of PHP by the PHP community. The extension can be enabled in php.ini and controlled via a set of directives that govern whether the cache is active, how much memory it may use, how string interning behaves, and how strictly source changes are detected. Management and monitoring can be performed at runtime with APIs such as opcache_get_status() and opcache_reset().

In operation, OPcache keeps the compiled code in shared memory so all PHP worker processes on the same machine can reuse it. It can also be configured to use a file cache for sharing caches across systems in certain deployments. Typical deployment guidance includes setting opcache.enable to yes, tuning opcache.memory_consumption to fit available RAM, and adjusting validation and preloading settings for reliability and performance.

OPcache is widely used in production PHP deployments and is considered a standard performance optimization tool for PHP applications.