opcache¶

Each run starts PHP, and stops it: what opcache compiled is gone with it. With PHP 8.5 and later, opcache can keep it in files of the WASM filesystem, in /opcache, that the next runs read instead of compiling the PHP files again. OPCACHE says when it compiles them:

• none, the default: every run compiles what it runs;
• runtime: as they run, the first run that needs a file compiles it, and writes it;
• precompiled: when PHP is built, after WARMUP. Every .php file of the embedded directory is compiled, and what opcache writes is embedded.

What it changes¶

With the Symfony example, in node:

The boot is bin/console doctrine:schema:update, the first run of the page. WARMUP alone, bin/console cache:warmup, saves the compilation of the container. Writing the cache makes the first runs slower, with runtime. precompiled costs what is embedded: opcodes are bigger than the PHP files, 46 MB for the 16 MB of the 3,932 PHP files of the example, in the .wasm file (13 MB with brotli, 5.2 MB without), and in the memory of the module (MEMORY, see Build arguments): 73 MB of its 128 MB before it runs, 26 MB without.

How it works¶

opcache checks the mtime of a file: one written over is compiled again, an embedded one too. Its mtimes are in seconds: it does not cache a file written less than 2 s before, it could be written again in the same second. What is embedded dates from 1970-01-01 00:00:01 (filemtime() gives 1): opcache caches it from the first run, and the build compiles it with this date.

opcache_invalidate() does nothing, and opcache_get_status() is false: opcache only has the files, no shared memory. A php.ini changes its settings, at /usr/local/lib/php.ini, written before the first run.

On 32 bits, what the module is, the file cache of PHP 8.5.12 and before breaks the attributes of constants, as the #[Deprecated] of symfony/polyfill-uuid: PHP crashes on such a file, or loses them (GH-24745). The build applies the fix of PHP 8.5.13 to these versions.