$this->db->trans_begin();
$q1 = $this->db->query("INSERT INTO `test`(`test_col`) VALUES ('aaaaaa')");
sleep(100000);
$q2 = $this->db->query("INSERT INTO `test`(`test_col`) VALUES ('bbbbbb')");
$this->db->trans_complete();

$this->db->trans_begin();
$q1 = $this->db->query("INSERT INTO `test`(`test_col`) VALUES ('duplicated')");
$q2 = $this->db->query("INSERT INTO `test`(`test_col`) VALUES ('new row')");
$this->db->trans_complete();

if ($this->db->trans_status() === FALSE) {
    // I get this line, but trans_rollback doesn't work
    $this->db->trans_rollback();
}