As discussed on emacs-help  I'm posting this example here which
reorders the file and runs slowly.

Though it's an sql dump file with long lines, the file is navigable without
any problem or slowness. Only this snippet runs slowly.

Here's the snippet:

(progn
  (goto-char (point-min))
  (when (search-forward "INSERT INTO `test2` (`aa`, `bb`) VALUES" nil t)
    (beginning-of-line)
    (while (looking-at "INSERT INTO `test2`.+,\\([0-9]+\\));")
      (let ((item (match-string 1))
            (line (buffer-substring (line-beginning-position) (line-end-position))))
        (message item)
        (save-excursion
          (re-search-backward (concat "INSERT INTO `test1`.+"
                                      "VALUES ("
                                      item
                                      ","))
          (end-of-line)
          (insert "\n" line))
        (delete-region (line-beginning-position) (1+ (line-end-position)))
        ))))


And the example file to run it on  is attached. (anonymized sql dump)