Capacity planning is difficult for DBAs who expect growth. Will there be enough CPU, Memory or I/O to serve the anticipated load? One category falls outside those three, logical contention.
Logical contention is a problem where excessive blocking causes throughput to suffer. It would be great to get advanced warning. One essential strategy is to make use of the blocked process report. The problem is that blocked process reports are an alarm metric, not a guage metric. In other words, the blocked process report can indicate when there is a problem, but it is poor at giving advanced notice.
This is a nice visual tool to begin to understand the topic. The same principles apply to road traffic, water flow, etc.