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

From: Maxim Yegorushkin
Subject: Re: emacs-24.1.1 slow scrolling in Fundamental mode with font lock disabled
Date: Mon, 12 Nov 2012 16:23:50 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121016 Thunderbird/16.0.1

On 12/11/12 16:19, Eli Zaretskii wrote:
From: Maxim Yegorushkin <>
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
08:35:28.217216000 167.250000  54888
2012-10-09 08:35:28.233155000 167.150000  66035
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

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

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