With a single latch, serialization is ensured, but concurrency is severely limited. All it takes is one other process requesting the latch while it's being held for contention to result. In this example, simply adding one more latch could solve the problem. Scale this out quite a bit by having hundreds or thousands of processes requiring access to the CBCs, and you can see the potential exists for serious performance-limiting concurrency issues.

Fortunately, by default, Oracle creates thousands of CBC latches. While Figure 6-9 shows 3 latches, real Oracle systems will have at least 10,000 chains and 1,000 latches.

One way to look at the contention possibility is to calculate how many chains each latch protects. For example, if there are 10,000 chains and 1,000 latches, then each latch ensures serialization for 10 chains.