What is a small party ? Is 9 considered a small party?

Yes

Definitely, I would recommend that you call ahead. Oliver Garden can get quite busy sometimes.

9 is a pretty fair size and depending on the day you're going you would definitely want to call ahead and let the restaurant know you're brining a party of 9 to their restaurant. This helps them prepare a space for the group and gives everyone in the restaurant including the kitchen a heads up. Always note when you call ahead they could be booked prior to that as well and won't always guarantee you a spot. Olive Garden is general is fairly busy especially during the dinner hours.