Interesting Ruby Resources

Posted by Alexander Todorov on Wed 23 December 2015

During my quest for faster RSpec tests I've come across several interesting posts about Ruby. Being new to the language they've helped me understand a bit more about the internals. Posting them here so they don't get lost.

Garbage Collection

The road to faster tests - a story about tests and garbage collection.

Tuning Ruby garbage collection for RSpec - practical explanation of Ruby's garbage collector and how to adjust its performance for RSpec

Demystifying the Ruby GC

Probably the very first posts I found referencing slow RSpec tests. It turned out this was not the issue but I've nevertheless tried running GC manually. I can clearly see (using puts GC.count in after()) GC invoked less frequently, memory usage rising but the overall execution time wasn't affected. The profiler said 2% speed increase to be honest.


Not being very clear about the different profiling tools available and how to interpret their results I've found these articles:

Profiling Ruby With Google's Perftools - practical example for using perftools.rb

How to read ruby profiler's output - also see the Profiler__ module

Show runtime for each rspec example - using rspec --profile

Suggestions for Faster Tests

Several general best practices for faster tests:

9 ways to speed up your RSpec tests

Run faster Ruby on Rails tests

Three tips to improve the performance of your test suite

RubyGems related

I've noticed Bundler loading tons of requirements (nearly 3000 unique modules) and for some particular specs this wasn't necessary (for example running Rubocop). I've found the following articles below which sound very reasonable to me:

Use Bundler.setup Instead of Bundler.require

5 Reasons to Avoid Bundler.require

Why "require 'rubygems'" Is Wrong


Finally (or more precisely first of all) I've seen this Weird performance issue.

During my initial profiling I've seen (and still see) a similar issue. When calling require it goes through lots of hoops before finally loading the module. My profiling results show this taking a lot of time but this time is likely measured with profiling enabled and doesn't represent the real deal.

On my MacBook Air with Red Hat Enterprise Linux 7 this happens when using Ruby 2.2.2 from Software Collections. If using Ruby installed from source with rbenv the profiling profile is completely different.

I will be examining this one in more details. I'm interested to know what is the difference and if that affects performance somehow so stay tuned!

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