begin (Vapor::Transaction)

    # File vapor/transaction.rb, line 38
        def begin
          unless @active
            @datastore.begin_transaction
            unless @persistence_manager.autocommit_in_progress?
              @persistence_manager.autocommit = false
            end
            @log = TransactionLog.new
            @log.committer = @committer
            @active = true
          else
            raise NestedTransactionError
          end
        end