Faster Pathname handling for Ruby written in Rust
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Latest commit ca470d4 Aug 4, 2018


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This gem shaves off more than 30% of my Rails application page load time.

The primary GOAL of this project is to improve performance in the most heavily used areas of Ruby as path relation and file lookup is currently a huge bottleneck in performance. As this is the case the path performance updates will likely not be limited to just changing the Pathname class but also will be offering changes in related methods and classes.

Users will have the option to write their apps directly for this library, or they can choose to either refine or monkeypatch the existing standard library. Refinements are narrowed to scope and monkeypatching will be a sledge hammer ;-)


I read a blog post about the new Sprockets 3.0 series being faster than the 2.0 series so I tried it out. It was not faster but rather it made my website take 31.8% longer to load. So I reverted back to the 2.0 series and I did a check on Rails on what methods were being called the most and where the application spends most of its time. It turns out roughly 80% (as far as I can tell) of the time spent and calls made are file Path handling. This is shocking, but it only gets worse when handling assets. That is why we need to deal with these load heavy methods in the most efficient manner!

Here's a snippet of a Rails stack profile with some of the most used and time expensive methods.

Booting: development
Endpoint: "/"
       user     system      total        real
100 requests 26.830000   1.780000  28.610000 ( 28.866952)
Running `stackprof tmp/2016-06-09T00:42:10-04:00-stackprof-cpu-myapp.dump`. Execute `stackprof --help` for more info
  Mode: cpu(1000)
  Samples: 7184 (0.03% miss rate)
  GC: 1013 (14.10%)
     TOTAL    (pct)     SAMPLES    (pct)     FRAME
      1894  (26.4%)        1894  (26.4%)     Pathname#chop_basename
      1466  (20.4%)         305   (4.2%)     Pathname#plus
      1628  (22.7%)         162   (2.3%)     Pathname#+
       234   (3.3%)         117   (1.6%)     ActionView::PathResolver#find_template_paths
      2454  (34.2%)          62   (0.9%)     Pathname#join
        57   (0.8%)          52   (0.7%)     ActiveSupport::FileUpdateChecker#watched
       760  (10.6%)          47   (0.7%)     Pathname#relative?
       131   (1.8%)          25   (0.3%)     ActiveSupport::FileUpdateChecker#max_mtime
        88   (1.2%)          21   (0.3%)     Sprockets::Asset#dependency_fresh?
        18   (0.3%)          18   (0.3%)     ActionView::Helpers::AssetUrlHelper#compute_asset_extname
       108   (1.5%)          14   (0.2%)     ActionView::Helpers::AssetUrlHelper#asset_path

Here are some additional stats. From Rails loading to my home page, these methods are called (not directly, Rails & gems call them) this many times. And the home page has minimal content.

Pathname#to_s called 29172 times.
Pathname#<=> called 24963 times.
Pathname#chop_basename called 24456 times
Pathname#initialize called 23103 times.
File#initialize called 23102 times.
Pathname#absolute? called 4840 times.
Pathname#+ called 4606 times.
Pathname#plus called 4606 times.
Pathname#join called 4600 times.
Pathname#extname called 4291 times.
Pathname#hash called 4207 times.
Pathname#to_path called 2706 times.
Pathname#directory? called 2396 times.
Pathname#entries called 966 times.
Dir#each called 966 times.
Pathname#basename called 424 times.
Pathname#prepend_prefix called 392 times.
Pathname#cleanpath called 392 times.
Pathname#cleanpath_aggressive called 392 times.
Pathname#split called 161 times.
Pathname#open called 153 times.
Pathname#exist? called 152 times.
Pathname#sub called 142 times.

After digging further I've found that Pathname is heavily used in Sprockets 2 but in Sprockets 3 they switched to calling Ruby's faster methods from File#initialize and Dir#each. It appears they've written all of the path handling on top of these themselves in Ruby. They achieved some performance gain by switching to rawer code methods, but then they lost more than that in performance by the many method calls built on top of that.

If you want to see the best results in Rails with this gem you will likely need to be using the Sprockets 2.0 series. Otherwise this library would need to rewrite Sprockets itself.

I've said this about Sprockets but this required two other gems to be updated as well. These are the gems and versions I upgraded and consider group 1 (Sprockets 2) and group 2 (Sprockets 3). My data is based on method calls rather than source code.

Sprockets 2 Group Sprockets 3 Group
sprockets 2.12.4 sprockets 3.6
sass 3.2.19 sass 5.0.4
bootstrap-sass bootstrap-sass 3.3.6

Performance Specifics

The headline for the amount for improvement on this library is specific to only the improvement made with the method chop_basename. Just so you know; in my initial release I had a bug in which that method immediately returned nothing. Now the good thing about this is that it gave me some very valuable information. First I found that all my Rails site tests still passed. Second I found that all my assets no longer loaded in the website. And third, and most importantly, I found my Rails web pages loaded just more than 66% faster without the cost of time that chop_basename took.

That's right; the path handling for assets in your website *consumes more than 2/3rds of your websites page load time.

So now we have some real numbers to work with We can be generoues and use 66% as our margin of area to improve over (for chop_basename specifically, not counting the benefit from improving the performance in other file path related methods). That means we want to remove as much of that percentage from the overall systems page load time. The original headline boasts over 33% performance improvement — that was when chop_basename was improved by just over 50%. Now chop_basename is improved by 83.4%. That alone should make your site run 55.044% faster now (given your performance profile stats are similar to mine).

What Rails Versions Will This Apply To?

As mentioned earlier Sprockets, which handles assets, changed away from using Pathname at all when moving from major version 2 to 3. So if you're using Sprockets 3 or later you won't reap the biggest performance rewards from using this gem for now (it's my goal to have this project become a core feature that Rails depends on and yes… that's a big ask). That is unless you write you're own implementation to re-integrate the use of Pathname and FasterPath into your asset handling library. For now just know that the Sprockets 2 series primarily works with Rails 4.1 and earlier. It may work in later Rails versions but I have not investigated this.


  • Rust compilation is working
  • Methods are stable
  • Thoroughly tested
  • Testers and developers are most welcome
  • Windows & encoding support is underway!


Ensure Rust is installed:

Rust Downloads

curl -sSf | sh

Add this line to your application's Gemfile:

gem 'faster_path', '~> 0.3.10'

And then execute:

$ bundle

Or install it yourself as:

$ gem install faster_path

Visual Benchmarks

Benchmarks in Faster Path now produce visual graph charts of performance improvements. When you run export GRAPH=1; bundle && rake bench the graph art will be placed in doc/graph/. Here's the performance improvement result for the chop_basename method.

Visual Benchmark


Add the proper require to your project.

require "faster_path"

Current methods implemented:

FasterPath Rust Implementation Ruby 2.5.0 Implementation Time Shaved Off
FasterPath.absolute? Pathname#absolute? 95.3%
FasterPath.add_trailing_separator Pathname#add_trailing_separator 48.4%
FasterPath.basename File.basename 12.0%
FasterPath.children Pathname#children 34.4%
FasterPath.chop_basename Pathname#chop_basename 83.4%
FasterPath.cleanpath_aggressive Pathname#cleanpath_aggressive 94.1%
FasterPath.cleanpath_conservative Pathname#cleanpath_conservative 93.5%
FasterPath.del_trailing_separator Pathname#del_trailing_separator 85.4% Pathname#directory? 6.4%
FasterPath.dirname File.dirname 55.4%
FasterPath.entries Pathname#entries 41.0%
FasterPath.extname File.extname 63.1%
FasterPath.has_trailing_separator? Pathname#has_trailing_separator 88.9% Pathname#join 79.1% Pathname#plus 94.7%
FasterPath.relative? Pathname#relative? 92.6%
FasterPath.relative_path_from Pathname#relative_path_from 93.3%

You may choose to use the methods directly, or scope change to rewrite behavior on the standard library with the included refinements, or even call a method to monkeypatch everything everywhere.

For the scoped refinements you will need to

require "faster_path/optional/refinements"
using FasterPath::RefinePathname

And for the sledgehammer of monkey patching you can do

require "faster_path/optional/monkeypatches"

Optional Rust implementations

These are stable, not performant, and not included in Pathname by default.

These will not be included by default in monkey-patches. To try them with monkeypatching use the environment flag of WITH_REGRESSION. These methods are here to be improved upon.

FasterPath Implementation Ruby Implementation
FasterPath.entries_compat Pathname.entries
FasterPath.children_compat Pathname.children

It's been my observation (and some others) that the Rust implementation of the C code for File has similar results but performance seems to vary based on CPU cache on possibly 64bit/32bit system environments. These are not included by default when the monkey patch method FasterPath.sledgehammer_everything! is executed.

Getting Started with Development

The primary methods to target are mostly listed in the Why section above. You may find the Ruby source code useful for Pathname's Ruby source, C source, tests, and checkout the documentation.

Methods will be written as exclusively in Rust as possible. Even just writing a not in Ruby with a Rust method like !absolute? (not absolute) drops 39% of the performance already gained in Rust. Whenever feasible implement it in Rust.

After checking out the repo, make sure you have Rust installed, then run bundle. Run rake test to run the tests, and rake bench for benchmarks.

Building and running tests

First, bundle the gem's development dependencies by running bundle. Rust compilation is included in the current rake commands.

FasterPath is tested with The Ruby Spec Suite to ensure it is compatible with the native implementation, and also has its own test suite testing its monkey-patching and refinements functionality.

To run all the tests at once, simply run rake. To run all the ruby spec tests, run mspec.

To run an individual test or benchmark from FasterPath's own suite:

# An individual test file:
ruby -I lib:test test/benches/absolute_benchmark.rb
# All tests:
rake minitest

To run an individual ruby spec test, run mspec with a path relative to spec/ruby_spec, e.g.:

# A path to a file or a directory:
mspec core/file/basename_spec.rb
# Tests most relevant to FasterPath:
mspec core/file library/pathname
# All tests:


Bug reports and pull requests are welcome on GitHub at


MIT License or APACHE 2.0 at your pleasure.