Re: emacs-24.1.1 slow scrolling in Fundamental mode with font lock disabled

[Maxim Yegorushkin]

On 12/11/12 16:19, Eli Zaretskii wrote:
> > From: Maxim Yegorushkin <maxim.yegorushkin@gmail.com>
> > Date: Mon, 12 Nov 2012 12:49:51 +0000
> >
> > I have 9Mb text file with 90000+ lines in it. When opening this file in
> > emacs-24.1.1 and scrolling to line 5000 and onwards the scrolling
> > becomes very slow and there is a long delay after I press PageDown and
> > emacs updates the view.
> >
> > I heard that font lock may cause this so I disabled font lock in that
> > buffer. Disabling font lock doesn't resolve the issue or speed things up
> > a bit.
> >
> > The contents of the file look like this:
> >
> > 2012-10-09 08:35:28.217216000 167.150000  44035
> > 2012-10-09 08:35:28.217216000 167.200000   2859
> >                                                   2012-10-09
> > 08:35:28.217216000 167.250000  54888
> > 2012-10-09 08:35:28.233155000 167.150000  66035
> >                                                   2012-10-09
> > 08:35:28.233155000 167.250000  44404
> >
> > (long line wrapped in the above).
> >
> > I.e. there is a timestamp on each line of it in the form of YYYY-MM-DD
> > HH:MM:SS.nnnnnnnnn.
> >
> > I almost accidentally replaced all 2012-10-09 with YYYY-MM-DD in the
> > file and that fixed the issue, the scrolling became swift again.
> >
> > Do you guys have any clues what may be causing this scrolling slowness
> > and why replacing ISO dates with YYYY-MM-DD makes scrolling so much
> > faster? (once again I have font lock disabled in that buffer).
>
> Does scrolling become faster if you type this:
>
>    M-x set-variable RET bidi-paragraph-direction RET left-to-right RET
>
> If it does,

It does indeed fixes the problem.

> then I believe this is an inefficiency in the
> bidirectional display engine that is already fixed in the development
> sources, and will be part of the upcoming Emacs 24.3 release.  If you
> can try the development sources, I think you should see that this
> problem is gone.

Thanks a lot Eli. I will stick this customization in .emacs for now.

-- Maxim