OPcache

Also Known As

TL;DR

Explanation

OPcache (bundled since PHP 5.5) stores compiled PHP bytecode in shared memory so subsequent requests skip the parse-and-compile phase. It can reduce CPU usage by 50–90% for busy applications. Key configuration settings include opcache.memory_consumption (typically 128–256 MB), opcache.max_accelerated_files (set above your file count), opcache.validate_timestamps (disable in production for maximum speed; invalidate cache on deploy), and opcache.jit_buffer_size (PHP 8.0+ JIT). Misconfigured OPcache can expose cached files to other processes — ensure opcache.restrict_api is set appropriately.

Common Misconception

Why It Matters

Common Mistakes

• Leaving OPcache disabled in production because it was absent from the default php.ini.
• Setting opcache.validate_timestamps=1 in production — defeats caching by checking file mtimes on every request.
• Forgetting to restart PHP-FPM after deploying — stale bytecode serves old code until the cache expires.
• Setting opcache.memory_consumption too low — cache eviction under memory pressure causes random misses.

Code Examples

; php.ini — OPcache not configured, effectively disabled
; opcache.enable=0

; php.ini production settings
opcache.enable=1
opcache.memory_consumption=256
opcache.max_accelerated_files=20000
opcache.validate_timestamps=0  ; clear cache on deploy instead

References

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

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