RackGcProfiler

A rack middleware for measuring GC activity during a request.

Add this line to your application's Gemfile:

gem 'rack_gc_profiler'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack_gc_profiler

Install the middleware into your application's list of rack middlewares.

Issue a request to your application. Two extra headers will be appended to the response:

$ curl -v -o /dev/null -sSq yourapp.example.com
< HTTP/1.1 200 OK
   :
< GC-Runs: 1
< GC-Time: 0.040000
  :
{ [1219 bytes data]
* Connection #0 to host yourapp.example.com left intact

GC-Runs is the number of times garbage collection ran during the request. GC-Time is the duration of all the GC runs that occured, in seconds.

Should you use this in production? Profiling anything always adds overhead. To measure this more concretely, a benchmark has been provided. See benchmark.rb in the root of the repo. On my machine, using MRI 2.3.1, GC profiling added 0.6% overhead. This equates to about 1.2ms on a 200ms request. Always evaluate in your own production environment first and decide for yourself before adding this to a production application.

To prevent information leakage, the reverse proxy upstream from your application server should log and delete the two headers listed in the section above.

To install in rails, add the following to your application.rb:

config.middleware.use RackGcProfiler::Middleware

See the Rails rack guide for more details.

To install in sinatra, add the following to your application:

use RackGcProfiler::Middleware

See the Sinatra docs for more details.

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/aasmith/rack_gc_profiler.

The gem is available as open source under the terms of the MIT License.