I was happily refactoring my messy vimrc, trying to emulate how the legendary junegunn does his. However, I realised that Vim was becoming less and less responsive the more I type. It appeared that the issue only plagued me when I was editing my vimrc, but not any other files. Needless to say, I was extremely annoyed. I was determined to identify the cause of the problem, and solve it.
During my investigation, I read up quite a bit on debugging Vim. Some of the noteworthy things I discovered include this helpful guide for troubleshooting Vim. I also found this great plugin called Bisectly that automates the plugin bisection process. By the way, if you are unfamiliar with the concept of bisection, you can read up more about it here. After much effort, I found that the issue could be attributed to these following three factors.
Factor #1: File Length
It turns out that my vimrc file was getting longer and longer. Writing more comments and functions made my code much more readable and understandable, but it also increased the file length. By right, going from 500 lines to 700 lines should not drastically impact the performance of Vim. Yet, it did. This served as an insight to the second factor in this problem. When a file gets longer, the syntax highlighting takes significantly more effort to work properly.
Factor #2: Regex Engine
Vim’s syntax highlighting relies on the regex engine. Typing
will show you all the syntax items that are active for the current
buffer. All that pattern matching requires a fast and reliable regex
engine for the syntax highlighting to feel seamless. Every time you
scroll the page, it takes a toll on the regex engine. If it is not
performant enough, the screen will start to lag as Vim furiously tries
to redraw the screen with new highlights. Vim 7.4 introduced a shiny,
new regex engine, but many people beg to differ.
Factor #3: Relative Number
The last thing that caught me by surprise was
seems like people have reported performance issues with relative number
when syntax highlighting is enabled. You can read more about the
issue on GitHub.
Funnily enough, relative number was actually the biggest issue.
Disabling it with
set norelativenumber in my vimrc immediately
solved the problem. Unfortunately, I really cannot live without a
life-changing feature like relative number. The Vim
team did release a patch to address the bug,
but applying means rebuilding Vim from its source with the patch applied
manually. To me, it was just too much work.
On the other hand, many people suggest reverting
to the old regex engine with
set re=1, especially for Ruby
development. So, I decided to give it a shot. It was a godsend. Vim felt
so much faster and responsive with that one extra line in my vimrc.
Since I dislike short forms, I went with this:
You can read the entry about the option with
:help regexengine. Of
course, we could also disable syntax highlighting completely with
:syntax off. That would literally solve the root of the problem, if
you could live with a life without colours.