How can I get large amount of data by an ajax call using .NET webservice ?

$.ajax({
      type: "POST",
      url: "Service.asmx/CreateReport",
      data: "{'reportname':'" + ReportID + "','datasourceid':'" + DataSourceId[i] + "','parameter':'" + Parameter + "'}",
      contentType: "application/json; charset=utf-8",
      dataType: "json",
      async: false,
      index: i,

      success: function (response) {
          numberofquery = numberofquery + 1;
          var Query = response.d;
          //alert(Query);

          store_data(Query, this.index);

          function store_data(Query, i) {
              try {
                  if (Query != null || Query != "") {

                      Query = JSON.parse(Query);


                      window[QueryName[i]] = [];

                      window[QueryName[i]] = Query;

                  }

              }

              catch (err) { }
          }


      },

      async: true,


      error: function (msg)
      {
          numberofquery = numberofquery + 1;
          CustomAlertShow("Error");
      },

      complete: function () {

          //GenerateAllReports();
          //console.log("numq=" + numberofquery + ",totalq=" + totalquery);
          if (numberofquery == totalquery) GenerateWithReloadedData();
      },

  });

[WebMethod]
    [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
    public string CreateReport(string reportname, string datasourceid, string parameter)
    {

        try
        {
            DataSet dataSet1 = new DataSet();
            SqlConnection cn1 = new SqlConnection(ConStr);

            string queryString = "Select ReportID, DataSourceID from dbo.ReportDataSourceDataModel " 

            SqlDataAdapter daGlobalClass = new SqlDataAdapter(queryString, cn1);

            cn1.Open();


            daGlobalClass.Fill(dataSet1, "myDataTable");

            cn1.Close();

            return JsonConvert.SerializeObject(dataSet1.Tables[0]);


        }
        catch (SqlException ex)
        {

            return "-ERR: " + DisplaySqlErrors(ex);

        }
    }