Have you noticed you’ll pull up the performance tab on Oracle Enterprise Manager and notice the graph is very choppy or wavy, like the ocean. You start wondering what is going on, but find nothing. I saw this enough times that I started looking into it. What I found was that it seems to only happen when you first login to OEM, and then it smooths out. At a conference I asked an Oracle employee who was presenting on ASH. His response was that Oracle hadn’t figured it out yet, but were aware of it.
So, if you’re trying to figure out why this happens, well, I don’t know, but don’t spend too much time trying figure it out.
The following image shows an example of this. The first graph shows my waits after having OEM open for a while. I then logged out of OEM, and logged back in. The second graph shows how it looked when I logged back in (note the time range is the same, and only offset by a couple minutes). You can see the spikes that don’t appear in the first. The third is the same session, but watching it for a while – you’ll notice it levels back out.