Blog post: Speed Tracer Server-side Tracing with Rack

Rack::SpeedTracer middleware provides server-side tracing capabilities to any Rack compatible app. Include the middleware, instrument your application, and then load it in your Google Chrome + SpeedTracer to view detailed breakdown of your JavaScript/CSS load times, GC cycles, as well as, server side performance data provided by this middleware - you can preview both server side and client side performance data all within the same view in SpeedTracer!

Preview of a sample, server side Rails trace (see below for setup) in SpeedTracer:

• Auto Rails 3 instrumentation (see example below)
• Memory, or Redis storage backend
  • Redis backend allows trace expiration (via :trace_ttl), and custom namespaces (via :namespace)

• Authentication / optional enable, ala rack-bug: IP-based, password based
  • At the moment, every request will record & store a trace
  • Could also do conditional tracing based on a request header: 'X-SpeedTracer: true'

Without authentication, I wouldn't recommend running this middleware in production, unless you add some extra logic. For a capped memory footprint, use Redis backend with a TTL to expire your traces after some reasonable amount of time.

Rack::SpeedTracer provides a Tracer class which you can use to instrument your code. From there, the trace details are stored as a JSON blob, and a special X-TraceUrl header is sent back to the client. If the user clicks on the network resource that corresponds to a request which returned a X-TraceUrl header, then SpeedTracer will make a request to our app to load the server side trace. Rack::SpeedTracer responds to this request and returns the full trace - aka, the data is provided on demand.

gem install rack-speedtracer

# in your rack app / rackup file
use Rack::SpeedTracer

# in your app
env['st.tracer'].run('name of operation') do
  ... your code ...
end

Check out a full sample rack app: examples/runner.rb

Rails 3 provides new Notifications API, which we can use to automatically instrument your Rails applications! It's as easy as:

# in your Gemfile
gem 'rack-speedtracer', :require => 'rack/speedtracer'

# in development.rb environment
config.middleware.use Rack::SpeedTracer

To produce a server-side trace equivalent to one in the screenshot above:

# in your Gemfile
gem 'rack-speedtracer', :require => 'rack/speedtracer'

# in development.rb environment
config.middleware.use Rack::SpeedTracer

# define a widgets controller
class WidgetsController < ApplicationController
  def index
    env['st.tracer'].run('Widgets#index') do
      env['st.tracer'].run("ActiveRecord: Widgets.all") do
        Widget.all
      end

      env['st.tracer'].run('Render') { render :text => 'oh hai' }
    end
  end
end

Speed Tracer is a Google Chrome extension to help you identify and fix performance problems in your web applications. It visualizes metrics that are taken from low level instrumentation points inside of the browser and analyzes them as your application runs. Speed Tracer is available as a Chrome extension and works on all platforms where extensions are currently supported (Windows and Linux).

Using Speed Tracer you are able to get a better picture of where time is being spent in your application. This includes problems caused by JavaScript parsing and execution, layout, CSS style recalculation and selector matching, DOM event handling, network resource loading, timer fires, XMLHttpRequest callbacks, painting, and more.

• Official SpeedTracer site
• Install SpeedTracer
• Getting Started
• Google Group

(The MIT License)

Copyright © 2010 Ilya Grigorik

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