The Wayback Machine - https://web.archive.org/web/20211006154237/https://www.php.net/manual/vote-note.php?id=95340&page=features.persistent-connections&vote=up
There's a third case for PHP: run on a fastCGI interface. In this case, PHP processes are NOT destroyed after each request, and so persistent connections do persist. Set PHP_FCGI_CHILDREN << mysql's max_connections and you'll be fine.