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Jon Moss 353122c9da Speed up Time.zone.now
@amatsuda, during his RailsConf talk this past year, presented a
benchmark that showed `Time.zone.now` (an Active Support joint)
performing 24.97x slower than Ruby's `Time.now`. Rails master appears to
be a _bit_ faster than that, currently clocking in at 18.25x slower than
`Time.now`. Here's the exact benchmark data for that:

```
Warming up --------------------------------------
            Time.now   127.923k i/100ms
       Time.zone.now    10.275k i/100ms
Calculating -------------------------------------
            Time.now      1.946M (± 5.9%) i/s -      9.722M in   5.010236s
       Time.zone.now    106.625k (± 4.3%) i/s -    534.300k in   5.020343s

Comparison:
            Time.now:  1946220.1 i/s
       Time.zone.now:   106625.5 i/s - 18.25x slower
```

What if I told you we could make `Time.zone.now` _even_ faster? Well,
that's exactly what this patch accomplishes. When creating `ActiveSupport::TimeWithZone`
objects, we try to convert the provided time to be in a UTC format. All
this patch does is, in the method where we convert a provided time to
UTC, check if the provided time is already UTC, and is a `Time` object
and then return early if that is the case, This sidesteps having to continue on,
and create a new `Time` object from scratch. Here's the exact benchmark
data for my patch:

```
Warming up --------------------------------------
            Time.now   124.136k i/100ms
       Time.zone.now    26.260k i/100ms
Calculating -------------------------------------
            Time.now      1.894M (± 6.4%) i/s -      9.434M in   5.000153s
       Time.zone.now    301.654k (± 4.3%) i/s -      1.523M in   5.058328s

Comparison:
            Time.now:  1893958.0 i/s
       Time.zone.now:   301653.7 i/s - 6.28x slower
```

With this patch, we go from `Time.zone.now` being 18.25x slower than
`Time.now` to only being 6.28x slower than `Time.now`. I'd obviously love some
verification on this patch, since these numbers sound pretty interesting... :)

This is the benchmark-ips report I have been using while working on this:

```ruby
require 'benchmark/ips'

Time.zone = 'Eastern Time (US & Canada)'

Benchmark.ips do |x|
  x.report('Time.now') {
    Time.now
  }

  x.report('Time.zone.now') {
    Time.zone.now
  }

  x.compare!
end
```

cc @amatsuda
cc performance folks @tenderlove and @schneems

![Pretty... pretty... pretty good.](https://media.giphy.com/media/bWeR8tA1QV4cM/giphy.gif)
2016-10-02 15:12:46 -04:00
.github Add a note about adding CHANGELOG entries at the top of the file [ci skip] 2016-07-02 22:31:09 +05:30
actioncable Use websocket-client-simple instead of Faye as a websockets client 2016-10-02 12:25:33 +10:30
actionmailer Fix broken comments indentation caused by rubocop auto-correct [ci skip] 2016-09-14 18:26:32 +09:00
actionpack Remove obsolete comment about class-level respond_to 2016-10-01 14:29:42 +01:00
actionview Change render to support any hash keys in locals 2016-10-02 00:21:17 -07:00
activejob fix link to resque [ci skip] 2016-09-20 08:56:05 +09:00
activemodel Do not leak the Errors default proc when calling to_hash or as_json 2016-09-27 14:33:16 +02:00
activerecord Add missing require for zlib 2016-10-01 16:29:22 +02:00
activesupport Speed up Time.zone.now 2016-10-02 15:12:46 -04:00
ci normalizes indentation and whitespace across the project 2016-08-06 20:16:27 +02:00
guides add cached key to sql.active_record event [ci skip] 2016-10-02 13:29:17 +09:00
railties remove mongrel once again 2016-09-29 17:30:56 +09:00
tasks modernizes hash syntax in the rest of the project 2016-08-06 19:40:54 +02:00
tools fixes remaining RuboCop issues [Vipul A M, Xavier Noria] 2016-09-01 23:41:49 +02:00
.codeclimate.yml Generators and tests are under the same style rules 2016-07-27 20:26:39 -03:00
.gitattributes adds .gitattributes to enable Ruby-awareness 2016-03-16 11:15:22 +01:00
.gitignore .gitignore: Ignore .ruby-version in any subdir 2015-09-07 16:37:14 -07:00
.rubocop.yml Fix broken comments indentation caused by rubocop auto-correct [ci skip] 2016-09-14 18:26:32 +09:00
.travis.yml Remove Faye mode 2016-10-01 15:35:59 +09:30
.yardopts
CODE_OF_CONDUCT.md
CONTRIBUTING.md Add notes on cosmetic patches 2016-05-13 15:03:50 -04:00
Gemfile Use websocket-client-simple instead of Faye as a websockets client 2016-10-02 12:25:33 +10:30
Gemfile.lock Use websocket-client-simple instead of Faye as a websockets client 2016-10-02 12:25:33 +10:30
rails.gemspec applies new string literal convention in the gemspecs 2016-08-06 19:27:12 +02:00
RAILS_VERSION Start Rails 5.1 development 🎉 2016-05-10 03:46:56 -03:00
Rakefile Remove Faye mode 2016-10-01 15:35:59 +09:30
README.md Fix title of README according to Markdown conventions 2016-02-25 03:39:02 +01:00
RELEASING_RAILS.md fix grammar 2016-05-31 13:31:18 +05:30
version.rb Start Rails 5.1 development 🎉 2016-05-10 03:46:56 -03:00

Welcome to Rails

Rails is a web-application framework that includes everything needed to create database-backed web applications according to the Model-View-Controller (MVC) pattern.

Understanding the MVC pattern is key to understanding Rails. MVC divides your application into three layers, each with a specific responsibility.

The Model layer represents your domain model (such as Account, Product, Person, Post, etc.) and encapsulates the business logic that is specific to your application. In Rails, database-backed model classes are derived from ActiveRecord::Base. Active Record allows you to present the data from database rows as objects and embellish these data objects with business logic methods. You can read more about Active Record in its README. Although most Rails models are backed by a database, models can also be ordinary Ruby classes, or Ruby classes that implement a set of interfaces as provided by the Active Model module. You can read more about Active Model in its README.

The Controller layer is responsible for handling incoming HTTP requests and providing a suitable response. Usually this means returning HTML, but Rails controllers can also generate XML, JSON, PDFs, mobile-specific views, and more. Controllers load and manipulate models, and render view templates in order to generate the appropriate HTTP response. In Rails, incoming requests are routed by Action Dispatch to an appropriate controller, and controller classes are derived from ActionController::Base. Action Dispatch and Action Controller are bundled together in Action Pack. You can read more about Action Pack in its README.

The View layer is composed of "templates" that are responsible for providing appropriate representations of your application's resources. Templates can come in a variety of formats, but most view templates are HTML with embedded Ruby code (ERB files). Views are typically rendered to generate a controller response, or to generate the body of an email. In Rails, View generation is handled by Action View. You can read more about Action View in its README.

Active Record, Active Model, Action Pack, and Action View can each be used independently outside Rails. In addition to that, Rails also comes with Action Mailer (README), a library to generate and send emails; Active Job (README), a framework for declaring jobs and making them run on a variety of queueing backends; Action Cable (README), a framework to integrate WebSockets with a Rails application; and Active Support (README), a collection of utility classes and standard library extensions that are useful for Rails, and may also be used independently outside Rails.

Getting Started

  1. Install Rails at the command prompt if you haven't yet:

     $ gem install rails
    
  2. At the command prompt, create a new Rails application:

     $ rails new myapp
    

    where "myapp" is the application name.

  3. Change directory to myapp and start the web server:

     $ cd myapp
     $ rails server
    

    Run with --help or -h for options.

  4. Using a browser, go to http://localhost:3000 and you'll see: "Yay! Youre on Rails!"

  5. Follow the guidelines to start developing your application. You may find the following resources handy:

Contributing

We encourage you to contribute to Ruby on Rails! Please check out the Contributing to Ruby on Rails guide for guidelines about how to proceed. Join us!

Everyone interacting in Rails and its sub-projects' codebases, issue trackers, chat rooms, and mailing lists is expected to follow the Rails code of conduct.

Code Status

Build Status

License

Ruby on Rails is released under the MIT License.