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Here’s a list of some of the most commonly used Fundamental Formulae from a Performance modelling standpoint.
- X = C / T ………[ X = Throughput, C = Number of Completions, T = Total Elapsed Time]
- Di = Vi * Si ……… [D = Service Demand, V = Visit Count, S = Service Time]
- Uavg = X * Savg ……… [ Uavg = Utilization, X = Throughput, Savg = Service Time]
- Xmax < or = 1 / Smax ……… [ Xmax = Max Throughput, Smax = Max Service Time]
- Savg = B / C ……… [ Savg = Service Time, C = Completions]
- Ravg = Qt + Savg ……… [ R = Response Time, Q = Queuing Time, Savg = Service Time]
- Qavg = X * Qt ……… [ Q = Queue Length, Qt = Queuing Time, X = Throughput]
- N = (R+Z) * X : Little’s Law ……… [ N = Number in System, R = Response Time, X = Throughput, Z = Think Time]
Little’s Law provides a set of equations to understand the relationship between User Concurrency in a System, the Response time (Response = Wait time or Queue Time + Service Time) and the Transactional throughput.
Little’s Law was given to us by Prof. John Little (http://en.wikipedia.org/wiki/Little%27s_law).
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