Re: Accelerating Emacs?

[David Kastrup]

"Herbert Euler" <herberteuler@hotmail.com> writes:

>>From: Eli Zaretskii <eliz@gnu.org>
>>To: help-gnu-emacs@gnu.org
>>Subject: Re: Accelerating Emacs?
>>Date: Fri, 28 Oct 2005 10:23:46 +0200
>
> Now I must show what I did. First, I wrote a Lisp program to generate
> random data:
>
> (let ((i 0))
>   (while (< i 20000)
>     (let ((j 0) s)
>       (while (< j 10)
>       (setq s (concat s (char-to-string (+ 50 (random 50))))
>             j (1+ j)))
>       (insert s "\n"))
>     (setq i (1+ i))))

This is not good in any programming language, as it has quadratic time
behavior.

_Buffers_ are the data structures for inserting text, not strings.  So
you better write:

(dotimes (i 20000)
  (dotimes (j 10)
    (insert-char (+ 50 (random 50))))
  (insert-char ?\C-j))

> I found Emacs used more and more memory when generating random data,
> so did when it replacing. These memory is released after Emacs
> finishes its job. Is this because Emacs operating buffer residing in
> memory?

No, it is because of nonsensical accumulation of strings which are
only garbage-collected from time to time.

> This happens when I am testing a 100MB size file. I go to the beginning
> of the file, press C-SPACE, then go to the end of the file, press M-w.

Don't do that, then.  Use delete-region instead of kill-region, or the
region will end up in the kill ring, where it still occupies memory.
And you might want to disable the undo history as well.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum