“
Performance Tactics on the Road Tactics are generic design principles. To exercise this point, think about the design of the systems of roads and highways where you live. Traffic engineers employ a bunch of design “tricks” to optimize the performance of these complex systems, where performance has a number of measures, such as throughput (how many cars per hour get from the suburbs to the football stadium), average-case latency (how long it takes, on average, to get from your house to downtown), and worst-case latency (how long does it take an emergency vehicle to get you to the hospital). What are these tricks? None other than our good old buddies, tactics. Let’s consider some examples: • Manage event rate. Lights on highway entrance ramps let cars onto the highway only at set intervals, and cars must wait (queue) on the ramp for their turn. • Prioritize events. Ambulances and police, with their lights and sirens going, have higher priority than ordinary citizens; some highways have high-occupancy vehicle (HOV) lanes, giving priority to vehicles with two or more occupants. • Maintain multiple copies. Add traffic lanes to existing roads, or build parallel routes. In addition, there are some tricks that users of the system can employ: • Increase resources. Buy a Ferrari, for example. All other things being equal, the fastest car with a competent driver on an open road will get you to your destination more quickly. • Increase efficiency. Find a new route that is quicker and/or shorter than your current route. • Reduce computational overhead. You can drive closer to the car in front of you, or you can load more people into the same vehicle (that is, carpooling). What is the point of this discussion? To paraphrase Gertrude Stein: performance is performance is performance. Engineers have been analyzing and optimizing systems for centuries, trying to improve their performance, and they have been employing the same design strategies to do so. So you should feel some comfort in knowing that when you try to improve the performance of your computer-based system, you are applying tactics that have been thoroughly “road tested.” —RK
”
”