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由 Stan Hu 提交于
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
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