Provides eager loading of Action View templates.
This optimization aims to improve cold render times and to allow more memory to be shared via CoW on forking web servers.
For more information see:
- Aaron Patterson's RailsConf 2019 Keynote
- John Hawthorn's "Parsing and Rewriting Ruby Templates" (slides)
Should I use this?
You probably don't need to.
This gem provides a place to test out an optimization we hope to eventually include in Rails where everyone can gain this benefit without any additional work or configuration
That said, it shows promising results today
The most likely downside of using this is that if this mispredicts render calls it will waste a little memory (somewhat ironically, since one goal is to save memory).
How it works
The main challenge in precompiling these templates is determining the locals they're going to be passed. Without the initialization, local vars look the same as method calls, so we need to compile separate copies for each different set of local variable passed in.
We determine the locals passed to each template by parsing all templates looking for render calls and extracting the local keys passed to that.
Right now this assumes every template with the same
virtual_path takes the same locals (there may be smarter options, we just aren't doing them).
A curse/blessing/actually still a curse of this approach is that mis-predicting render calls doesn't cause any issues, it just wastes RAM.
Templates are half-compiled using standard Action View handlers, so this should work for erb/builder/haml/whatever.
Parsing is done using either Ruby 2.6's
RubyVM::AbstractSyntaxTree or JRuby's parser.
Add this line to your application's Gemfile:
And then execute:
$ bundle install
To precompile views on app boot, create an initializer to perform precompilation
# config/initializers/actionview_precompiler.rb ActionviewPrecompiler.precompile
It can also be run in verbose mode, which I use to tell which views it has detected. I usually run this in a console
- Support more
- Parse controllers/helpers for more renders
- Cache detected locals to avoid parsing cost
- Upstream more bits to Rails
After checking out the repo, run
bin/setup to install dependencies. Then, run
rake test to run the tests. You can also run
bin/console for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run
bundle exec rake install. To release a new version, update the version number in
version.rb, and then run
bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the
.gem file to rubygems.org.
Bug reports and pull requests are welcome on GitHub at https://github.com/jhawthorn/actionview_precompiler. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.
Code of Conduct
Everyone interacting in the ActionviewPrecompiler project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.