Looking at XenForo_Application::loadDb() and XenForo_Db::_execQuery(), I notice there's support for the pdo_mysql driver in XenForo. Or at least it was intended to provide support for pdo_mysql. But switching the adapter class via config.php doesn't really work seamlessly. Code: $config['db']['adapter'] = 'pdo_mysql'; (1) XenForo_Install_Model_Upgrade::getLatestUpgradeVersionId() now returns a string (correct data type for fetchOne, according to the published API) instead of an integer; which breaks any version checking. (2) Starting a nested transaction results in an sql error, sometimes. Happens just randomly. Couldn't find any pattern to it. (3) The forumlist page works, though. And it consistently loads ~15% faster with pdo, than with mysqli. Is it just me? And what's the status of PDO_MySql in XenForo: fully supported?