why CTAS faster than Insert select?

Hi,

I've been testing the performance between Create Table As Select (CTAS) vs Insert Select for large volume of data (40 million records or so). Both in nologging mode, parallel, etc. It consistently shows that CTAS faster than Insert Select. My understanding is that, if you parallel both create/insert process and select process, then theoratically they should perform about the same (same amount of work, same number of parallel processes, minimum redo and undo...). Could anybody explain why this is the case?

Thanks,
Linda Received on Tue Mar 29 2005 - 12:46:14 CST