Tracking slow SQL queries in Codeigniter

// index.php
$ci = & get_instance();
$handle = fopen('slow_query_1.log', "a+");
$handle_slow = fopen('slow_query_10.log', "a+");
foreach($ci->db->queries as $key =>$query)
{
    $time = number_format($ci->db->query_times[$key], 4);
    if ($time < 1)
        continue;
    if ($time < 10)
    {
        fwrite($handle, date('j.m.Y G:i:s').' : '.$time."\r\n");
        fwrite($handle, $query."\r\n\r\n-----------------------------\r\n");
    }
    else
    {
        fwrite($handle_slow, date('j.m.Y G:i:s').' : '.$time."\r\n");
        fwrite($handle_slow, $query."\r\n\r\n-----------------------------\r\n");
    }
}
fclose($handle);
fclose($handle_slow);