SOM plot - hangs?

I have around 20000 rows in my Database table. When I tried to do SOM Plot view, it hangs for a long time (progress button hangs at last-but-two step), after pressing the 'Calculate' button. Is this a bug? If not, please let me know how to proceed with this?
Note: I have already changed the values for plotter.rows.maximum to 20000.