$dbconfig['db_type'] = 'mysqli';

vtigerlibrariesadodbdriversadodb-mysqli.inc.php

if ($ok) {
        if ($argDatabasename)  return $this->SelectDB($argDatabasename);
        return true;
} else {
        if ($this->debug)
            ADOConnection::outp("Could't connect : "  . $this->ErrorMsg());
        $this->_connectionID = null;
        return false;
}

if ($ok) {
        mysqli_query($this->_connectionID, "SET SESSION sql_mode = 'TRADITIONAL'");
        if ($argDatabasename)  return $this->SelectDB($argDatabasename);
        return true;
} else {
        if ($this->debug)
            ADOConnection::outp("Could't connect : "  . $this->ErrorMsg());
        $this->_connectionID = null;
        return false;
}