In Ruby 2.3 or later, `String#+@` is available and `+@` is faster than `dup`.

```ruby
# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  gem "benchmark-ips"
end

Benchmark.ips do |x|
  x.report('+@') { +"" }
  x.report('dup') { "".dup }
  x.compare!
end
```

```
$ ruby -v benchmark.rb
ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]
Warming up --------------------------------------
                  +@   282.289k i/100ms
                 dup   187.638k i/100ms
Calculating -------------------------------------
                  +@      6.775M (± 3.6%) i/s -     33.875M in   5.006253s
                 dup      3.320M (± 2.2%) i/s -     16.700M in   5.032125s

Comparison:
                  +@:  6775299.3 i/s
                 dup:  3320400.7 i/s - 2.04x  slower

```

This reverts commit 3420a145, reversing
changes made to afb66a5a.

Plus a couple of related ActionPack patches.

Implement naive partial caching mechanism.

Add test for LogSubscriber

Use ActionView::Base#log_payload to store log_subscriber's payload, so we can pass cache result into it.

Fixed tests

Remove useless settings

Check if #log_payload exists before calling it. Because other classes also includes CacheHelper but don't have is attribute

Use @log_payload_for_partial_reder instead of #log_payload to carry ActionView's payload.

Update test's hash syntax

Add configuration to enable/disable fragment caching logging

Remove unless test and add new test to ensure cache info won't effect next rendering's log

Move :enable_fragment_cache_logging config from ActionView to ActionPack

Apply new config to tests

Update actionview's changelog

Update configuration guide

Improve actionview's changelog

Refactor PartialRenderer#render and log tests

Mute subscriber's log instead of disabling instrumentation.

Fix typo, remove useless comment and use new hash syntax

Improve actionpack's log_subscriber test

Fix rebase mistake

Apply new config to all caching intstrument actions

We don't need to use active support in this case because we know the
type that will be returned.

Referencing Rails.env without checking if it's defined couples
us to Railties.

Fix by avoiding the line breaks if we don't have an env check
to rely on.

- Fixes #23428.

I wrote a utility that helps find areas where you could optimize your program using a frozen string instead of a string literal, it's called [let_it_go](https://github.com/schneems/let_it_go). After going through the output and adding `.freeze` I was able to eliminate the creation of 1,114 string objects on EVERY request to [codetriage](codetriage.com). How does this impact execution?

To look at memory:

```ruby
require 'get_process_mem'

mem = GetProcessMem.new
GC.start
GC.disable
1_114.times { " " }
before = mem.mb

after = mem.mb
GC.enable
puts "Diff: #{after - before} mb"

```

Creating 1,114 string objects results in `Diff: 0.03125 mb` of RAM allocated on every request. Or 1mb every 32 requests.

To look at raw speed:

```ruby
require 'benchmark/ips'

number_of_objects_reduced = 1_114

Benchmark.ips do |x|
  x.report("freeze")    { number_of_objects_reduced.times { " ".freeze } }
  x.report("no-freeze") { number_of_objects_reduced.times { " " } }
end
```

We get the results

```
Calculating -------------------------------------
              freeze     1.428k i/100ms
           no-freeze   609.000  i/100ms
-------------------------------------------------
              freeze     14.363k (± 8.5%) i/s -     71.400k
           no-freeze      6.084k (± 8.1%) i/s -     30.450k
```

Now we can do some maths:

```ruby
ips = 6_226k # iterations / 1 second
call_time_before = 1.0 / ips # seconds per iteration 

ips = 15_254 # iterations / 1 second
call_time_after = 1.0 / ips # seconds per iteration 

diff = call_time_before - call_time_after

number_of_objects_reduced * diff * 100

# => 0.4530373333993266 miliseconds saved per request
```

So we're shaving off 1 second of execution time for every 220 requests. 

Is this going to be an insane speed boost to any Rails app: nope. Should we merge it: yep. 

p.s. If you know of a method call that doesn't modify a string input such as [String#gsub](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37) please [give me a pull request to the appropriate file](https://github.com/schneems/let_it_go/blob/b0e2da69f0cca87ab581022baa43291cdf48638c/lib/let_it_go/core_ext/string.rb#L37), or open an issue in LetItGo so we can track and freeze more strings. 

Keep those strings Frozen

![](https://www.dropbox.com/s/z4dj9fdsv213r4v/let-it-go.gif?dl=1)

The Logger by default includes a guard which checks for the
logging level. By removing the custom logging guards, we can decouple
the logging guard from the logging action to be done.

This also follows the good practice listed on http://guides.rubyonrails.org/debugging_rails_applications.html#impact-of-logs-on-performance.

Simple Sungularize ActionController::UnpermittedParameters error in case when only 1 parameter is unpermitted.

deep_munge solves CVE-2013-0155 security vulnerability, but its
behaviour is definately confuisng. This commit adds logging to deep_munge.
It logs keys for which values were set to nil.

Also mentions in guides were added.

Log 'Filter chain halted as CALLBACKNAME rendered or redirected' every time a before callback halts.

make the logs a little simpler to view, put the render message inline with other events, pull processing to char[0] and add a new line to the completed. looks more like a block now, which is useful for serial actions like test/dev

A patch so that http status codes are still included in logs even during an exception [#6333 state:resolved]
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Signed-off-by: NJosé Valim <jose.valim@gmail.com>

Move Rails::LogSubscriber to ActiveSupport::LogSubscriber, allowing frameworks like ActiveRecord and ActiveResource to log outsude Rails::Application [#4816 state:resolved]