I first presented on Oracle 10g Block Change Tracking Internals at UKOUG 06 in Birmingham. It was very well received, but there were quite a few gaps in my knowledge, and I later discovered I was incorrect in some places. I’ve done some additional research, filled in the blanks and corrected in a few places.
The wrong part concerned which processes track changes in blocks. I assumed it was database writers when in fact it’s a shadow process changing the block that produces change-tracking entries. I also added details on how this info is passed to CTWR process, which SGA memory areas are used for that, and how both of these impacted by the number of CPUs. In addition, I mentioned hidden parameters that are related to block change tracking.
The presentation and white paper are available for download. If you didn’t happen to be at the presentation itself, I suggest you look at the paper rather than the slides — it has more details and is easier to follow.
Unfortunately, I focused too much while preparing on the new areas I wanted to cover in this session, and didn’t invest enough time in reviewing the whole presentation and old material. Imagine my shame and embarrassment when I actually forgot a few slides and had to actually look at some of them for few seconds to recall what they were about. I also found that the audience was less interested than that at UKOUG in this level of internals. In the end, the presentation didn’t go as well as it did in Birmingham, so I learned an important lesson this day: never overestimate your knowledge of the topic and always vigorously review your presentations, even those repeatedly delivered.
Nevertheless, there were folks very interested in the details and since I was getting those much-needed nods during my session, I had some confirmation that the audience (or at least part of it) was following the thread. I think next time I should include the demo in presentations with a similar level of internal details — that should make it a much better experience and more lively for the audience.