class ActiveRecord::ConnectionAdapters::TransactionInstrumenter

def start
  raise InstrumentationAlreadyStartedError.new("Called start on an already started transaction") if @started
  @started = true
  ActiveSupport::Notifications.instrument("start_transaction.active_record", @base_payload)
  @payload = @base_payload.dup # We dup because the payload for a given event is mutated later to add the outcome.
  @handle = ActiveSupport::Notifications.instrumenter.build_handle("transaction.active_record", @payload)
  @handle.start
end