If you set sort_area_retained_size to 0, it will show as 0 in V$PARAMETER, but it defaults back to the value of sort_area_size when called upon. You can confirm this with event 10032. However, if the sort occurs in memory, then this does not matter, because there is no merge phase in a memory sort.

What if the sort_area_retained_size is set to 0. The sort occurs in memory and then what happens to the merge? Does the 0 setting for sort_area_retained_size cause a write to disk?