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.

In Figure 2-16, the top non-IO wait event is library cache latch contention. Is this an issue? While 85% of the non-IO wait time is related to library cache latch contention, the 5 seconds it consumes, compared to the total wait time of 621 seconds, are insignificant.