rack-objectspace

This is my attempt to make a rack middleware that profiles memory usage in rails (or any rack-based app), with the aim of detecting memory leaks. After every request it takes a dump of the objectspace and saves it to a data store of your choice*.

* Any object supporting the []= method can be used as a data-store. I recommend Moneta, which has support for Redis and Amazon S3.

Getting Started

After installing the gem, insert rack-objectspace into your middleware stack:

config.middleware.insert_after ActionDispatch::Static, Rack::Objectspace, store: Moneta.new(:Redis)

I'd recommend installing rack-objectspace as low as you can in your stack. Preferably only requests that hit your own application code should be profiled.

Warnings

DO NOT USE THIS IN PRODUCTION (it's VERY slow - I'd recommend running it on a close-copy of production instead)

Every objectspace dump is unique to a particular ruby process. Make sure your server is only running a single worker when profiling.

I've found that with unicorn, requests will usually time-out when using rack-objectspace. Try increasing the timeout value in unicorn.rb.

How to find memory leaks

Right now this bit is manual. rack-objectspace will give you the objectspace for a running app. I'd recommend taking the objectspace dumps for several successive requests and looking for objects that aren't garbage collected, as @wagenet did in his post on the Skylight blog.

Credits

This project was heavily inspired by blog posts by @samsaffron and @wagenet. I take no credit for the technique used here.

Also, many thanks to @newbamboo for letting me work on this during office hours.