Opcode Caching

Also Known As

TL;DR

Explanation

PHP normally parses and compiles source files on every request. Opcode caching (via OPcache, the standard built-in extension since PHP 5.5) stores the compiled bytecode in shared memory so subsequent requests for the same file skip compilation entirely. This can improve throughput by 50–90% for typical applications. The JIT compiler introduced in PHP 8.0 extends this further by compiling hot bytecode to native machine code. Proper OPcache configuration (adequate memory, file count, and deployment cache-clear strategy) is essential in production.

Common Misconception

Why It Matters

Common Mistakes

• Not enabling OPcache in production — it is often off by default in minimal PHP installs.
• Setting opcache.validate_timestamps=1 in production — checks file mtimes on every request, negating half the benefit.
• Not setting opcache.memory_consumption large enough — cache evictions cause repeated recompilation.
• Deploying new code without restarting PHP-FPM or touching opcache.php — stale bytecode serves old code.

Code Examples

; php.ini — OPcache disabled or misconfigured:
;opcache.enable=1          ; Commented out — no caching
opcache.memory_consumption=64  ; Too small for large frameworks — use 256+
opcache.validate_timestamps=1  ; File stat on every request in production — set to 0

; php.ini — OPcache production settings
opcache.enable=1
opcache.memory_consumption=256     ; MB — size to your codebase
opcache.interned_strings_buffer=16
opcache.max_accelerated_files=20000
opcache.validate_timestamps=0      ; disable in production — manual invalidation
opcache.revalidate_freq=0
opcache.save_comments=1            ; needed for PHPDoc-based tools

; After deploy — invalidate stale cache
; opcache_reset(); or restart PHP-FPM
php -r 'opcache_reset();'
; Or per file: opcache_invalidate('/var/www/app/bootstrap.php', true);

References

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

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