Middleware for measuring Rack-based web applications. Part of the Rails Google Summer of Code '09 quartet.
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README.markdown

Dtracy, or How To Soon Spot Trends in your Web Application and Server

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Dtracy is part of the Ruby on Rail's Google Summer of Code '09 Quartet, with development updates and entertainment available at http://ecin.tumblr.com Welcome! Sit down, grab a sugary drink, and enjoy the smell of freshly baked code right out of the oven.

requirements

An operating system with support for Dtrace (http://www.sun.com/bigadmin/content/dtrace/) is a must. Mac OS X, Solaris/OpenSolaris and FreeBSD are all acceptable choices, though you're hardcore if you get Dtrace running properly on FreeBSD.

A courageous heart will also come in handy: this is still alpha software.

gem dependencies

running locally

The running process will require root privileges in order to access the Dtrace probes. As such, sudo bin/server will run rackup with examples/dtracy.ru as a rackup file on port 3000.

hello world - a brief overview

Actually, I don't mean to be pretentious. "hello 4 or 5 curious developers" is a better name for this section.

Digression aside, Dtracy is divided into two areas: Rack::Probe and Dtracy::App. They're both written as Rack middleware to allow easy dropping into other apps, with Rack::Probe handling the definition and consumption of Dtrace probes while Dtracy::App is meant to provide visualizations to the data generated from the aforementioned probes.

When running bin/server, the Dtracy::App app gets loaded, providing a list of activated probes and an inconspicuous ring at /__dtracy__/. Requests made to the server will fire the rack*:ruby:path:path probe setup in examples/dtracy.ru. In short:

  • Point a browser at localhost:3000/__dtracy__/
  • Drag and drop the rack*:ruby:path:path div/string onto the ring; it should start spinning
  • curl localhost:3000/[any path] several times
  • Watch the ring spin faster; this is due to the probe firing for each request made
  • ab -n100 http://127.0.0.1:3000/[any path] if you feel like hosing the application

Feel free to visit /__dtracy__/updates to see what kind of JSON data gets generated by the active probes.