class ActiveRecord::ConnectionAdapters::TransactionManager

def begin_transaction(isolation: nil, joinable: true, _lazy: true)
  @connection.lock.synchronize do
    run_commit_callbacks = !current_transaction.joinable?
    transaction =
      if @stack.empty?
        RealTransaction.new(
          @connection,
          isolation: isolation,
          joinable: joinable,
          run_commit_callbacks: run_commit_callbacks
        )
      else
        SavepointTransaction.new(
          @connection,
          "active_record_#{@stack.size}",
          @stack.last,
          isolation: isolation,
          joinable: joinable,
          run_commit_callbacks: run_commit_callbacks
        )
      end
    if @connection.supports_lazy_transactions? && lazy_transactions_enabled? && _lazy
      @has_unmaterialized_transactions = true
    else
      transaction.materialize!
    end
    @stack.push(transaction)
    transaction
  end
end