b02458ef52
In Rails 5, including `ActionView::Context` can have a significant and
hidden performance penalty because this module also includes
`ActionView::CompiledTemplates`. This means that any module that
includes ActionView::Context becomes a descendant of
`CompiledTemplates`.
When a partial is rendered for the first time, it runs
`ActionView::CompiledTemplates#module_eval`, which will evaluate a
string that defines a new method for that partial. For example, the
source of partial might be this string:
```
def _app_views_project_show_html_haml___12345(local_assigns, output)
"hello world"
end
```
When this string is evaluated, the Ruby interpreter will define the
method and clear the global method cache for all descendants of
`ActionView::CompiledTemplates`. Previous to this change, we
inadvertently made a number of modules fall into this category:
* GroupChildEntity
* NoteUserEntity
* Notify
* MergeRequestUserEntity
* AnalyticsCommitEntity
* CommitEntity
* UserEntity
* Kaminari::Helpers::Paginator
* CurrentUserEntity
* ActionView::Base
* ActionDispatch::DebugExceptions::DebugView
* MarkupHelper
* MergeRequestPresenter
After this change:
* Kaminari::Helpers::Paginator
* ActionView::Base
* ActionDispatch::DebugExceptions::DebugView
Each time a partial is rendered for the first time, all methods for
those modules will have to be redefined. This can exact a significant
performance penalty.
How bad is this penalty? Using the following benchmark script, we can
use DTrace to sample the Ruby interpreter:
```
Benchmark.bm do |x|
x.report do
1000.times do
ActionView::CompiledTemplates.module_eval("def testme\nend")
end
end
end
```
This revealed a 11x jump in the time spent in `core#define_method`
alone.
Rails 6 fixes this behavior by moving the `include CompiledTemplates`
into ActionView::Base so that including `ActionView::Context` doesn't
quietly affect other modules in this way.
Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/11198
41 lines
1.6 KiB
Ruby
41 lines
1.6 KiB
Ruby
# frozen_string_literal: true
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# This file was simplified from https://raw.githubusercontent.com/rails/rails/195f39804a7a4a0034f25e8704220e03d95a752a/actionview/lib/action_view/context.rb.
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#
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# It is only needed by modules that need to call ActionView helper
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# methods (e.g. those in
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# https://github.com/rails/rails/tree/c4d3e202e10ae627b3b9c34498afb45450652421/actionview/lib/action_view/helpers)
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# to generate tags outside of a Rails controller (e.g. API, Sidekiq,
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# etc.).
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#
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# In Rails 5, ActionView::Context automatically includes CompiledTemplates.
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# This means that any module that includes ActionView::Context is now a descendant
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# of CompiledTemplates.
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#
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# When a partial is rendered for the first time, it runs
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# Module#module_eval, which will evaluate a string source that defines a
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# new method. For example:
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#
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# def _app_views_profiles_show_html_haml___1285955918103175884_70307801785400(local_assigns, output_buffer)
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# "hello world"
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# end
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#
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# When a new method is defined, the Ruby interpreter clears the method
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# cache for all descendants, and all methods for those modules will have
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# to be redefined. This can lead to a significant performance penalty.
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#
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# Rails 6 fixes this behavior by moving out the `include
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# CompiledTemplates` into ActionView::Base so that including `ActionView::Context`
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# doesn't quietly affect other modules in this way.
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if Rails::VERSION::STRING.start_with?('6')
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raise 'This module is no longer needed in Rails 6. Use ActionView::Context instead.'
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end
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module Gitlab
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module ActionViewOutput
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module Context
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attr_accessor :output_buffer, :view_flow
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end
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end
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end
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