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From: Maxim Yegorushkin <maxim.yegorush...@gmail.com>
Newsgroups: gnu.emacs.help
Subject: Re: emacs-24.1.1 slow scrolling in Fundamental mode with font lock
	disabled
Date: Mon, 12 Nov 2012 16:23:50 +0000
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On 12/11/12 16:19, Eli Zaretskii wrote:
>> From: Maxim Yegorushkin <maxim.yegorush...@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