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Re: Handling large files with Emacs

From: Eli Zaretskii
Subject: Re: Handling large files with Emacs
Date: Wed, 24 Oct 2012 20:16:12 +0200

> From: Tom <>
> Date: Wed, 24 Oct 2012 09:34:41 +0000 (UTC)
> Jambunathan K <kjambunathan <at>> writes:
> > >
> > > I think it's because syntax highlight or something. When I try opening
> > > SQL dumps (say, 200MB) then Emacs grinds to a halt for a minute or
> > > so, and moving in the file is very slow even after that.
> > 
> > Have you experimented with `font-lock-maximum-size' together with
> > `font-lock-support-mode'?
> > 
> Not yet, because I rarely need this and if I do then it's simpler to open
> the file in fundamental mode.
> But the real question is if font locking is really  the cuplrit then why
> do we need to resort such special settings? We have fast enough computers
> and AFAIK jit font-lock is the default, so it should not be a problem.

And it isn't a problem, indeed, unless the mode in question does
something pathological with its definition of font-lock-keywords etc.

> Even if lisp perfomance cannot be improved much, font lock should be
> clever enough to stay in the background and do stealth fontification
> on remote parts of the large buffer only if the user is idle and only
> in chunks, so it can yield to user input. Isn't this what JIT font-lock
> is supposed to do in the first place?

It is, and it does.  But whenever you scroll to another portion in the
buffer, JIT font-lock fontifies the displayed portion before
displaying it, which could slow down redisplay, regardless of stealth.

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