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1.2 The Role of Performance Requirements in Performance Engineering

To ensure that performance needs are met, it is important that they be clearly specified in requirements early in the software development cycle. Early and concise specifications of performance requirements are necessary because:

  • Performance requirements are potential drivers of the system architecture and the choice of technologies to be used in the system’s implementation. Moreover, many performance failures have their roots in poor architectural choices. Modification of the architecture before a system is implemented is cheaper than rebuilding a slow system from scratch.
  • Performance requirements are closely related to the contractual expectations of system performance negotiated between buyer and seller, as well as to any relevant regulatory requirements such as those for fire alarm systems.
  • The performance requirements will be reflected in the performance test plan.
  • Drafting and reviewing performance requirements force the consideration of trade-offs between execution speed and system cost, as well as between execution speed and simplicity of both the architecture and the implementation. For instance, it is more difficult to design and correctly code a system that uses multithreading to achieve parallelism in execution than to build a single-threaded implementation.
  • Development and/or hardware costs can be reduced if performance requirements that are found to be too stringent are relaxed early in the software lifecycle. For example, while a 1-second average response time requirement may be desirable, a 2-second requirement may be sufficient for business or engineering needs. Poorly specified performance requirements can lead to confusion among stakeholders and the delivery of a poor-quality product with slow response times and inadequate capacity.
  • If a performance issue that cannot be mapped to explicit performance requirements emerges during testing or production, stakeholders might not feel obliged to correct it.

We shall explore the principles of performance requirements in Chapter 5.

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