Re: replace regex takes long

[Eli Zaretskii <eliz@gnu.org>]

> From: Gary Wessle <phddas@yahoo.com>
> Date: 16 Apr 2006 09:35:00 +1000
> 
> Gary Wessle <phddas@yahoo.com> writes:
> 
> > Peter Dyballa <Peter_Dyballa@Web.DE> writes:
> > 
> > > Am 15.04.2006 um 23:29 schrieb Gary Wessle:
> > > 
> > > > M-x query-replace-regex <RET> +<RET><ONE SPACE>
> > > > the file size is 4162111 with 77000 lines on PentiumIII 500, it has
> > > > been 10 minutes so I opened another emacs processor to write and
> > > > post this.
> > > > is there a problem with my command and why it is taking that long?
> > > 
> > > Yes, because the command needs your co-operation. And if you don't
> > > press "yes" no change will be made.
> > 
> > if fact I forget to say that I did hit ! which means "replace all"
> with M-x regex-replace it shows (replaced 304172 occurrences) and it
> is taking more than 5 minutes now and still have not finished the
> task.

I just tried query-replace-regex on a file with the structure you
described, and the command ran to completion in just 40 seconds,
including 3 questions whether to discard undo info.  That was on a
3-GHz Pentium 4 in a buffer that is in Fundamental mode.  So your
timing seems very unusual, to say the least.

Do you have some specialized major mode in that buffer?  If so,
perhaps it slows down the replacement; try in Fundamental mode.  I'd
also suggest to try the command in "emacs -q", perhaps something in
your customizations slows down the replacements.

In any case, your command is wasteful because it forces Emacs to
replace even a single space.  I suggest to try this instead:

    M-x query-replace-regex <RET>  +<RET> <RET>
                                 ^^
                             two spaces here

This command takes just 20 seconds on my machine.

Btw, what version of Emacs do you have, and on which OS?