Determining the correct grid size is done through a process of trial and error. It is recommended that you set your grid size in relationship to the approximate size of the object that you are indexing. Grid sizes that are set too small or too large can result in slowed performance. Sizes that are set too small affect the key/object ratio during an index search. In this case, too many keys are created and a large number of candidates is returned. For grid sizes that are set too large, the initial index search returns a small number of candidates, but the performance might be slowed during the final table scan.
For more information about selecting grid cell sizes and the number of grid levels, see Selecting the grid cell size.