Add a column to a big table without downtime

gistfile1.rb

  disable_ddl_transaction!
  
  def up
    add_column :users, :processed, :boolean
    change_column :users, :processed, :boolean, default: false
    execute 'update users set processed = false where processed is null'
    add_index :users, :processed, where: 'processed = false', algorithm: :concurrently
  end