How does OPcache Preloading work in PHP 8.x, and how do you configure it in containerized production environments?

Real-World Scenario / Incident Description

Deploying a Docker container with PHP-FPM where cold requests experienced 200ms latency on the first 100 requests after deployment.

693 views • Updated 1 month ago

OPcache Preloading Mechanics

When PHP-FPM starts up, a designated preload script compiles specified classes, traits, and interfaces directly into permanent shared memory before any HTTP request is accepted:

opcache.preload=/var/www/preload.php
opcache.preload_user=www-data

Considerations & Gotchas

Preloaded classes are permanently bound in memory.
If code changes on disk, you must restart PHP-FPM (systemctl restart php-fpm) for preloaded memory to reload.
Preload only stable framework code (e.g. vendor/ and core service classes), not dynamically changing code.

Related Concepts: #OPcache #Preloading #Docker #DevOps #Performance

More Modern PHP 8.x & Internals Interview Questions

How does the Zend Engine manage memory with Zvals, Reference Counting, and the Circular Garbage Collector in PHP 8.x? Read → Explain PHP 8.4 Asymmetric Visibility, Property Hooks, and Constructor Property Promotion. Read → How does the JIT (Just-In-Time) compiler in PHP 8.x work, and why does it benefit CPU-heavy tasks but not typical database-heavy web apps? Read → How do PHP Fibers work under the hood, and how do they differ from full async threads (Go Goroutines / Node.js Event Loop)? Read → How do you stream and parse a 50GB JSON/CSV export file in PHP without exceeding a 128MB memory limit? Read →

Back to Modern PHP 8.x & Internals Questions