ghiculescu · June 17, 2021 19:20 · Jun 17, 2021
diff --git a/bench.rb b/bench.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require "bundler/inline"
+
+gemfile(true) do
+  source "https://rubygems.org"
+
+  git_source(:github) { |repo| "https://github.com/#{repo}.git" }
+
+  gem "rails", github: "rails/rails", branch: "main"
+  # gem "rails", github: "ghiculescu/rails", branch: "has-many-build-perf-regression"
+  gem "sqlite3"
+  gem "benchmark-ips"
+end
+
+require "active_record"
+require "active_support"
+require "logger"
+
+ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
+ActiveRecord::Base.logger = Logger.new(STDOUT)
+
+ActiveRecord::Schema.define do
+  create_table :authors, force: true do |t|
+  end
+  create_table :posts, force: true do |t|
+    t.references :author
+  end
+end
+
+class Author < ActiveRecord::Base
+  has_many :posts
+end
+
+class Post < ActiveRecord::Base
+  belongs_to :author
+end
+
+author = Author.create!
+
+posts = 100_000.times.map { |n| { author_id: author.id } }
+Post.insert_all(posts)
+
+author = Author.find(author.id)
+author.posts.load_target
+
+Benchmark.ips do |x|
+  x.report("main branch") { author.posts.build }
+  # x.report("my branch") { author.posts.build }
+  x.compare!
+end
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