The longest queue is going to be in front of the tightest bottleneck, but not the central bottleneck critical to your application. If you find you have a bottl

The longest queue is going to be in front of the tightest bottleneck, but not the central bottleneck critical to your application. If you find you have a bottleneck halfway through the pipe and you make that bottleneck go away, your true real bottleneck down in the wall still remains there, and all your optimizations done above that one will end up just opening the floodgates wider. Once you've protected that kind of more at-risk core, then it's easier and safer to measure everything that sits above it in the stack, and it puts an upper bound on how much you need to optimize (you stop when you hit your rate limits on the core component).