How to monitor table load?

I've got to make sure there is always enough space in my db so that new entries can be inserted. How to do that best?

Today I

• analyze my table to get average row length and number of rows
• then I compare avg_row_len*num_rows with initial_extend + (max_extends-1) * next_extend
• when actual load is close to the maximum size I delete some entries

But this apparently doesn't work. Oracle reports "max extends reached" (something like that) way before actual load is close to maximum load (~4GB). In fact it's only at about 60%.

Any ideas, hints?

Thanks in advance,
Rajk

-- 

Rajk Kaiser					Alcatel SEL AG Berlin
						Department VB/EFB	
phone:	  +49 30 7002 3112			Colditzstrasse 34-36
telefax:  +49 30 7002 3345			12099 Berlin           
e-mail:	  Rajk.Kaiser_at_bln.sel.alcatel.de	Germany