From /data/project/zoomviewer/public_html/index.php

$db = mysqli_connect("p:commonswiki.labsdb", $ts_mycnf['user'], $ts_mycnf['password'], "commonswiki_p");

From https://www.php.net/mysqli_connect:

Prepending host by p: opens a persistent connection.

From https://wikitech.wikimedia.org/wiki/Help:Toolforge/Database#Connection_handling_policy:

Usage of connection pools (maintaining open connections without them being in use), persistent connections, or any kind of connection pattern that maintains several connections open even if they are unused is not permitted on shared MySQL instances (Wiki Replicas and ToolsDB).