an approximation to an n-server capacity planner

# an approximation to an n-server capacity planner - A little...

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A little elaboration of capacity planning Dennis Shasha

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Capacity Planning Arrival Rate A1 is given as an assumption A2 = (0.4 A1) + (0.5 A2) A3 = 0.1 A2 Service Time (S) S1, S2, S3 are measured Utilization U = A x S Response Time R = U/(A(1-U)) = S/(1-U) (assuming Poisson arrivals) Entry (S1) 0.4 Search (S2) Checkout (S3) 0.5 0.1 Getting the demand assumptions right is what makes capacity planning hard
How to Handle Multiple Servers Suppose one has n servers for some task that requires S time for a single server to perform. The perfect parallelism model is that it is as if one has a single server that is n times as fast. However, this overstates the advantage of parallelism, because even if there were no waiting, single tasks require S time.

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Servers There are two components to response time: waiting time + service time. In the parallel setting, the service time is
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an approximation to an n-server capacity planner - A little...

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