This code is very strange. I ran it, and it is indeed very slow. But I think the problem is that you are creating a child band for every parent row. Why are you doing that? Is there some reason you need to create an entirely different band for each row in the parent band?

Thanks Mike for the prompt response.

Here is very simple sample code I put together that illustrates the problem. Without resetting DataSource it runs for ~8 seconds. When you first set DataSource to null, do your changes and set it back to ultraDataSource it takes less than a second.

//ultraGrid1.DataSource = null;

this.ultraGrid1.BeginUpdate();
this.ultraGrid1.SuspendRowSynchronization();
try
{
    UltraDataRow row = ultraDataSource1.Rows.Add(new object[] { "Data1", "Data2", "Data3", "Data4", "Data5" });
   
    for (int i = 0; i < 30; i++)
    {
        UltraDataBand band = ultraDataSource1.Band.ChildBands.Add(i.ToString());
        //don't know if there is an easier way to inherit parent band's columns
        foreach (UltraDataColumn column in ultraDataSource1.Band.Columns)
            band.Columns.Add(column.Key, column.DataType);

        UltraDataRow row2 = row.GetChildRows(band).Add(new object[] { "BandA", "Data2", "Data3", "Data4", "Data5" });               
    }

    //ultraGrid1.DataSource = ultraDataSource1;
}
finally
{
    this.ultraGrid1.ResumeRowSynchronization();
    this.ultraGrid1.EndUpdate();
}