OPS.10:4.3 - Choose the smallest adequate service analysis
| Receiving question | Appropriate first analysis | What it can establish |
|---|---|---|
| Can these known jobs fit the actual windows? | A finite schedule using arrival, readiness, service, calendar and precedence data, or a necessary time/resource bound. | A feasible assignment; impossibility only when a necessary bound or complete valid search excludes the deadline. |
| What is a useful mean steady-state screen? | A queueing approximation whose population, service, routing, stability and dependence assumptions fit. | A qualified mean estimate, not a tail guarantee. |
| What happens under a specified disruption or burst? | A trace replay or explicit stress schedule, with actual policy and resources. | A conditional scenario result, not its probability of occurrence. |
| Does a changing or coupled operation meet a probabilistic service target? | A stochastic model or simulation of the relevant inputs and policy, retaining parameter and model uncertainty. | A conditional service probability; reliance on actual service additionally needs the corresponding input and model basis. |
For a single continuously available compatible server operating first-come, first-served, a finite calculation can be very small. For each job in arrival order, start is the later of its arrival and the previous finish; finish is start plus service time; wait is start minus arrival. This assumes no other setup, interruption, precedence or resource requirement. Add those conditions to the schedule when they apply.
Do not use a steady-state approximation for a finite overload or changing regime merely because it yields a number. Correlated bursts, feedback, blocking, priorities and skill classes may require a different model. A specialist analysis is a named input with a receiving use, not a substitute for stating the operating question.