How to increase the Performance of the Select query fetching Huge data from database

 private void FetchDataToDataList()
    {DataTable dt = new DataTable();
        if (Cache["DataTable-cach"] == null)
        {
            String strConnString = System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
            SqlConnection con = new SqlConnection(strConnString);
            SqlCommand cmd = new SqlCommand("SELECT dbo.table_name.field_name, FROM dbo.table_name ", con);
            con.Open();
             dt = new DataTable("T");
             string startime = System.DateTime.Now.ToLongTimeString();
            dt.Load(cmd.ExecuteReader());
            string endtime = System.DateTime.Now.ToLongTimeString();
            Cache.Insert("DataTable-cach", dt, null, DateTime.Now.AddMinutes(5), System.Web.Caching.Cache.NoSlidingExpiration);
            con.Close();
        }
        else 
        {
            dt = ((DataTable)Cache["DataTable-cach"]);
        }

// pagedDS is data list control
        PagedDataSource pagedDS = new PagedDataSource();
        pagedDS.DataSource = dt.DefaultView;
        pagedDS.AllowPaging = true;
        pagedDS.PageSize = 6;
        pagedDS.CurrentPageIndex = CurrentPage;
        dlPaging.DataSource = pagedDS;
        dlPaging.DataBind();
        lblCurrentPage.Text =  pagedDS.PageCount.ToString() +" صفحه    " +  (CurrentPage + 1).ToString()+ " از " ;
        // Disable Prev or Next buttons if necessary
        cmdPrev.Enabled = !pagedDS.IsFirstPage;
        cmdNext.Enabled = !pagedDS.IsLastPage;
       
    }