Hi Vibhore,

      I have tried your scenario with our "Orders" table from Northwind database, and grouping performace only take a couple seconds to expand and collapse the row.

      However, here is the snippet to perform expand the group row from client side:

        function Button1_onclick() {
            var grid = ISGetObject("WebGrid1");
            grid.GetRootTable().GetGroupRows()[1].ExpandGroupRow();
        }

     function Button1_onclick() {
            var grid = ISGetObject("WebGrid1");
            grid.GetRootTable().GetGroupRows()[1].CollapseGroupRow();
        }

      I hope it helps. Thank you and have a nice day.

Best Regards,

Andi Santoso