neovim syntax highlight with large files issue

Question

I use neovim 0.4.3. When I open a large xml file (about 130-140k lines) syntax highlighting switches off with a message:

'redrawtime' exceeded, syntax highlighting disabled

If add this line to my config init.vim:

set redrawtime=10000

The syntax highlighting works but when I try to scroll up page by page it becomes really slow.

What can be a possible solution or I just need to accept the fact that there is no syntax highlighting for large files in neovim/vim?

Answer 1

Syntax for large files is consistently atrociously slow (especially when the language is hugely recursive à la lisp or xml: C fares much better because it has generally has more consecutive structures than recursive ones). I find it best to turn it off when viewing large documents.

I don’t have anything technical to back this up (links, discussion, timings, etc.), and I would greatly welcome an answer that did.

See also :syntime

One tweak can be bumping up the maxmempattern to let vim use more memory.

Answer 2

Syntax highlighting is done synchronously in vim, which is why it is slow when dealing with large files.

There's a few highlights you can deactivate to speed things up:

set nocursorline
set nocursorcolumn

You can also set the minimum / maximum highlighted lines (:h :syn-sync-maxlines):

syntax sync minlines=200
syntax sync maxlines=500

There's a good article about this on vim fandom.

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A better way to get fast and consistent highlights is to use the language server protocol.

It's not only for highlights though, its first use is indeed completion.

A few vim plugins can use the LSP, here's some of them:

• CoC (I use this one)
• Ale
• vim-lsp
• LanguageClient-neovim

Setting this up can be a bit tedious, but it's very powerful once it's done.

I'm not sure about the others, but CoC offers highlights out of the box.