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1.5 Disciplines and Techniques Used in Performance Engineering

The practice of performance engineering draws on many disciplines and skills, ranging from the technological to the mathematical and even the political. Negotiating, listening, and writing skills are also essential for successful performance engineering, as is the case for successful architects and product owners. The set of original undergraduate major subjects taken by performance engineers the author has met includes such quantitative disciplines as mathematics, physics, chemical engineering, chemistry, biology, electrical engineering, statistics, economics, and operations research, as well as computer science. Those who have not majored in computer science will need to learn about such subjects as operating systems design, networking, and hardware architecture, while the computer scientists may need to acquire additional experience with working in a quantitative discipline.

To understand resource usage and information flow, the performance engineer must have at least a rudimentary knowledge of computer systems architecture, operating systems principles, concurrent programming principles, and software platforms such as web servers and database management systems. In addition, the performance engineer must have a sound grasp of the technologies and techniques used to measure resource usage and traffic demands, as well as those used to drive transactions through a system under test.

To understand performance requirements and the way the system will be used, it is necessary to know something about its domain of application. The performance and reliability needs of financial transaction systems, fire alarm systems, network management systems, conveyor belts, telecommunications systems, train control systems, online news services, search engines, and multimedia streaming services differ dramatically. For instance, the performance of fire alarm systems is governed by building and fire codes in the jurisdictions where the systems will be installed, while that of a telephone system may be governed by international standards. The performance needs of all the systems mentioned previously may be driven by commercial considerations such as competitive differentiation.

Because performance is heavily influenced by congestion, it is essential that a performance engineer be comfortable with quantitative analysis methods and have a solid grasp of basic statistics, queueing theory, and simulation methods. The wide variety of computer technologies and the evolving set of problem domains mean that the performance engineer should have an eclectic set of skills and analysis methods at his or her disposal. In addition, it is useful for the performance engineer to know how to analyze large amounts of data with tools such as spreadsheets and scripting languages, because measurement data from a wide variety of sources may be encountered. Knowledge of statistical methods is useful for planning experiments and for understanding the limits of inferences that can be drawn from measurement data. Knowledge of queueing theory is useful for examining the limitations of design choices and the potential improvements that might be gained by changing them.

While elementary queueing theory may be used to identify limits on system capacity and to predict transaction loads at which response times will suddenly increase [DenningBuzen1978], more complex queueing theory may be required to examine the effects of service time variability, interarrival time variability, and various scheduling rules such as time slicing, preemptive priority, nonpreemptive priority, and cyclic service [Kleinrock1975, Kleinrock1976].

Complicated scheduling rules, load balancing heuristics, protocols, and other aspects of system design that are not susceptible to queueing analysis may be examined using approximate queueing models and/or discrete event simulations, whose outputs should be subjected to statistical analysis [LawKelton1982].

Queueing models can also be used in sizing tools to predict system performance and capacity under a variety of load scenarios, thus facilitating what-if analysis. This has been done with considerable commercial success. Also, queueing theory can be used to determine the maximum load to which a system should be subjected during performance tests once data from initial load test runs is available.

The performance engineer should have some grasp of computer science, software engineering, software development techniques, and programming so that he or she can quickly recognize the root causes of performance issues and negotiate design trade-offs between architects and developers when proposing remedies. A knowledge of hardware architectures, including processors, memory architectures, network technologies, and secondary storage technologies, and the ability to learn about new technologies as they emerge are very helpful to the performance engineer as well.

Finally, the performance engineer will be working with a wide variety of stakeholders. Interactions will be much more fruitful if the performance engineer is acquainted with the requirements drafting and review processes, change management processes, architecture and design processes, and testing processes. The performance engineer should be prepared to work with product managers and business managers. He or she will need to explain choices and recommendations in terms that are related to the domain of application and to the trade-offs between costs and benefits.

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