jimn1982,
Where did you get the information about "buffer descriptor"? How did you find it? If you copied the article from somewhere else, please tell us the location.
As far as I know, the term "buffer descriptor" is rarely used. When it *is* used, it simply refers to buffer header (BH). But buffer header exists all the time, not created at the time a query or DML starts.
Yong Huang