My shell is slooow!

This is my first blog post for years. I have been finding excuses for not writing one over the years, but I feel this is the right time.

I was coding as usual when I started something odd with my shell. I have done few adjustments to my .zshrc file and out of a sudden it became very slow to spawn a new shell. As a person who has a obsession with performance, it became my duty to find out the problem.

The culprit

I have done some measurements:

> time /bin/zsh -i -c exit
/bin/zsh -i -c exit  0.30s user 0.41s system 34% cpu 2.077 total

2 secs just for spawning a new shell? There is really something odd. Well at this point, I thought using some kind of profiler on my Mac like samples, but then I decided it will be simpler to go over the things on .zshrc file comment out some of them to find out what is causing this annoying lag.

After a while, I found 3 things:

[ -s "$NVM_ROOT/nvm.sh" ] && \. "$NVM_ROOT/nvm.sh"
[ -s "$NVM_ROOT/bash_completion" ] && \. "$NVM_ROOT/bash_completion"

export PATH=$RVM_ROOT/bin:$PATH
source $RVM_ROOT/scripts/rvm

export PATH=$PYENV_ROOT/bin:$PATH
eval "$(pyenv init --path)"

As you can see, I am frequently using nvm, rvm and pyenv. That is because my day-to-day job requires jumping between different versions of Node/Python/Ruby currently.

When I comment out above code, the startup time decreases to 0.153 from 2.077 :)

lazyload extension to the rescue

Most of the time, I don’t need these stuff to be initialized at all. However, I need them when I need them.

There is a extension called lazyload that takes a command and do the initialization only once when you need them. Within few minutes, I arrived at following code:

lazyload nvm -- '[ -s "$NVM_ROOT/nvm.sh" ] && \. "$NVM_ROOT/nvm.sh"
    [ -s "$NVM_ROOT/bash_completion" ] && \. "$NVM_ROOT/bash_completion"'

lazyload rvm -- 'export PATH=$RVM_ROOT/bin:$PATH
    source $RVM_ROOT/scripts/rvm'

lazyload pyenv -- 'export PATH=$PYENV_ROOT/bin:$PATH
    eval "$(pyenv init --path)"'

Which was exactly what I needed!

My full .zshrc file: https://github.com/sumerc/dotfiles/blob/main/zshrc

And the zsh-lazyload extension: https://github.com/qoomon/zsh-lazyload

One final thought

Right now, I am really wondering why these tools do not provide this kind of lazy-loading by default. It seems far better practice especially for people that have to install lots of different tools.