Note that invalidation doesn't actually evict anything from the cache, it just forces a recompile. You can verify this by calling opcache_get_status() and seeing that the invalidated script is not actually removed from "scripts". This means it cannot be used as a more graceful alternative to opcache_reset() when the cache is full ("cache_full":true in status). The cache will eventually fill up and refuse to cache new requests if you do atomic deployment of PHP code by changing the web server's document root. It appears opcache_reset() is the only way to prevent this, but opcache_reset() can disable the cache for any amount of time while attempting to restart, causing load spikes.