Поведение этих функций зависит от установок в php.ini.
Краткое разъяснение конфигурационных директив.
Enables or disables the plugin. If set to disabled, the extension will not allow users to plug into mysqlnd to hook mysqlnd calls.
Wheter to report wrong return value types of user hooks as error of the type E_WARNING. It is strongly recommended to use this setting for detecting possible issues.