Re: Accelerating Emacs?

[Eli Zaretskii <eliz@gnu.org>]

> From: "Herbert Euler" <herberteuler@hotmail.com>
> Date: Fri, 28 Oct 2005 13:53:08 +0800
> 
> >try fundamental-mode
> 
> I tried that, but it is only effective when making small
> changes i.e. deleting a character.

Well, your original complaint _was_ about deleting a single
character.  Are you on the quest to prove at all costs that Emacs is
slow?

> On my test on a 8612 KB size file, Emacs is not quick enough
> yet. The sed command
> 
>     sed 's/[A-Z]/0/g' test
> 
> needs 17s to finish its job, and vim command
> 
>     :1,$:s/[A-Z]/0/g
> 
> needs 1min 7s, but even 20min is still not enough for
> the Emacs command (in fundamental-mode)
> 
>     (replace-regexp "[A-Z]" "0" nil nil nil)

What kind of machine do you have there?  I tried this on a 3MB file
(my email inbox), and it took less than 1 minute, even though I needed
to answer the question about discarding undo info several times during
that time.  This is on a 3GHz Pentium 4 running Windows XP.  I then
tried the same with a 19MB email box on a 700MHz Pentium III running
Debian GNU/Linux, and it took 13 minutes there (vim did it in 30
seconds).  Perhaps you should upgrade your hardware?

Anyway, `replace-regexp' does much more than just replace its first
argument with the second, and those other things make it run slower.
The doc string for `replace-regexp' says (note the last part,
especially):

    This function is usually the wrong thing to use in a Lisp program.
    What you probably want is a loop like this:
      (while (re-search-forward regexp nil t)
	(replace-match to-string nil nil))
    which will run faster and will not set the mark or print anything.

> Besides, Emacs uses about 128MB memory.

??? Not unless you visit many large files, it isn't.  My Emacs session
where I'm typing this runs for many days, has gobs of files and
buffers in it, and still uses only 22MB of memory.

> And when I tried to mark all text, Emacs complains about the memory.

How much memory do you have on that machine (and what OS is that)?
Also, please tell what command you used ``to mark all text'', and what
was the exact language of the Emacs complaint about memory.

> So I think it is better of using tools such as sed and
> vim to edit file bigger than 5MB instead of Emacs,
> since Emacs is not good at this job.

You are entitled to decide whatever you wish, but this would be not a
very wise decision, I think.  It is based on an unrealistic example
(perform unrealistic replacement in an unrealistic file).  I'd advise
against such a decision.