As another example, suppose that you receive a call about long commit times. The users are saying "submits" or "saves" are taking longer today than yesterday. Upon an examination of the average log file sync wait times (which indicate commit times from an Oracle perspective), you discover there is no change from the previous day. Therefore, you know the performance issue is not because of Oracle's commit mechanism and most likely not related to the database.

Figure 2-16 shows a non-IO wait time summary, along with the underlying wait event detail. While most Oracle performance problems start out as an IO issue, after working on the problems, many turn into memory management issues. Depending on the event mix, sometimes I will perform an additional classification manually.

Starting with Oracle Database 10g, each latch of significance has its own wait event. If you want to know the total latch-related time, you'll need to sum the individual latch times. Usually, this is not necessary, even with severe latch contention, because one latch will dominate and be your main focal point.