freeze the column name to drop string allocations in dirty checks
Dirty checking keeps a hash where the keys are the column name and the value is a dup of the value from the database[1]. This hash is kept for every AR object, which means that we dup every column name for every AR object that does dirty checking. Freezing the column name prevents the column name from being duped and reduced overall string allocations. Here is a benchmark to demonstrate: ```ruby require 'active_record' class Topic < ActiveRecord::Base end 20.times do |i| Process.waitpid fork { ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:' ActiveRecord::Base.connection.instance_eval do create_table(:topics) do |t| t.string :title, limit: 250 t.string :author_name t.string :author_email_address t.string :parent_title t.string :type t.string :group i.times do |j| t.string :"aaa#{j}" end t.timestamps null: true end end ObjectSpace::AllocationTracer.setup(%i{type}) Topic.create title: "aaron" # heat cache result = ObjectSpace::AllocationTracer.trace do 10.times do |i| Topic.create title: "aaron #{i}" end end puts "#{Topic.columns.length},#{(result.find { |k,v| k.first == :T_STRING }.last.first / 10)}" } end ``` 1. https://github.com/rails/rails/blob/3ad381c3f8598d9920998c8949a96b5f62b280dd/activerecord/lib/active_record/attribute_set/builder.rb#L102
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