Just a quick observation...

It sounds like you are running a DSS application from the size... I doubt 4GB for TEMP is going to be anywhere near enough space...I've got about 40GB allocated to mine so far. It does depend on the application and what you are doing but 4GB seems like a small amount if you are running really large queries. Have you tuned your sort_area_size and TEMP tablespace? Also make sure that you create the temporary tablespace as type TEMP so Oracle will dynamically allocate and deallocate the space. Finally there is an issue with PMON not keeping up with cleanup. There is a way to force PMON to work a little harder to clean the space up - it is described on Steve Adams (author of OReilly's "Oracle 8i Internal Services for Waits, Locks, and Memory) Oracle internals site and a script is provided.

Finally ESTIMATE STATISTICS at 50% will actually do a compute statistics because the overhead isn't much different. I believe this happens at anything over 30% (it might be 40%, I can't remember, I'll go back and look it up later) but I know positively that 50% will just give you the same issue.

Joe