I need to find a really good intro to queuing theory to send people to. A full queue is a slow queue. You actually want to aim for about 65% utilization.
Also, there was a formula for determining the optimal cache size. I forget the name all the time. IIRC, in the end, caching most popular 10 items was enough to respond to 95% of your queries without hitting the disk.
If the numbers from the phoenix project are to be trusted, a loose estimate is the time spent in queue is proportional to the ratio of utilized to unutilized resources. For example, 50% used & 50% unused is 50:50 = 1 unit of time. 99% used is 99:1 = 99 units of time.
