OPcache Preloading (PHP 7.4)

TL;DR

Explanation

Configured with opcache.preload = /path/to/preload.php in php.ini. The preload script uses opcache_compile_file() or require to load files into shared memory. All PHP-FPM workers share this preloaded code. Gains: 10–30% performance improvement for frameworks (Symfony, Laravel). Limitation: preloaded code cannot be reloaded without restarting PHP-FPM — not suitable for development. opcache.preload_user specifies the user to run the preload script as. Frameworks generate preload scripts automatically. Ideal for production only.

Common Misconception

Why It Matters

Common Mistakes

• Enabling preloading in development — must restart FPM for code changes to take effect.
• Not regenerating the preload file after Composer updates.
• Preloading too much — only framework core, not application code.

Code Examples

# Development with preloading — requires FPM restart on every change:
; opcache.preload=/var/www/vendor/autoload.php

# Production php-fpm.conf:
[production]
opcache.preload=/var/www/config/preload.php
opcache.preload_user=www-data

# preload.php:
<?php
require '/var/www/vendor/autoload.php';
opcache_compile_file('/var/www/vendor/symfony/framework-bundle/FrameworkBundle.php');

References

• ↗ https://www.php.net/manual/en/opcache.preloading.php

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