Singed
Singed makes it easy to get a flamegraph anywhere in your code base. It wraps profiling your code with stackprof or rbspy, and then launching speedscope to view it.
Installation
Add to Gemfile:
gem "singed"
Then run bundle install
Then run npm install -g speedscope
Usage
Simplest is calling with a block:
flamegraph {
# your code here
}
Flamegraphs are saved for later review to Singed.output_directory, which is tmp/speedscope on Rails. You can adjust this like:
Singed.output_directory = "tmp/slowness-exploration"
Blockage
If you are calling it in a loop, or with different variations, you can include a label on the filename:
flamegraph("rspec") {
# your code here
}
You can also skip opening speedscope automatically:
flamegraph(open: false) {
# your code here
}
RSpec
If you are using RSpec, you can use the flamegraph metadata to capture it for you.
# make sure this is required at somepoint, like in a spec/support file!
require 'singed/rspec'
RSpec.describe YourClass do
it "is slow :(", flamegraph: true do
# your code here
end
end
Controllers
If you want to capture a flamegraph of a controller action, you can call it like:
class EmployeesController < ApplicationController
flamegraph :show
def show
# your code here
end
end
This won't catch the entire request though, just once it's been routed to controller and a response has been served (ie no middleware).
Rack/Rails requests
To capture the whole request, there is a middleware which checks for the X-Singed header to be 'true'. With curl, you can do this like:
curl -H 'X-Singed: true' https://localhost:3000
PROTIP: use Chrome Developer Tools to record network activity, and copy requests as a curl command. Add -H 'X-Singed: true' to it, and you get flamegraphs!
This can also be enabled to always run by setting SINGED_MIDDLEWARE_ALWAYS_CAPTURE=1 in the environment.
Command Line
There is a singed command line you can use that will record a flamegraph from the entirety of a command run:
$ bundle binstub singed # if you want to be able to call it like bin/singed
$ bundle exec singed -- bin/rails runner 'Model.all.to_a'
The flamegraph is opened afterwards.
Limitations
When using the auto-opening feature, it's assumed that you are have a browser available on the same host you are profiling code.
The open is expected to be available.