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Determining the Expected Demand

To determine the expected demand for resources of a system, capacity planners need to

determine individual demands of all the applications supported by the system. Later they can

aggregate those results to get idea about traffic pattern of the whole system. Understanding the

demand pattern of application is important as the traffic pattern generally changes with time.

Figure 10.5 shows sample graphs plotted from the recorded number of hits in a web

application viewed over a week and a year. Such statistics may give a fair idea regarding the

overall workload pattern of application.

From the weekly graph it can be seen that the spikes are not always of equal demand in

a single day. Sometimes it is high, sometimes low. The yearly graph provides idea about the

varying demand of an application over a year. The business goal of capacity planning is to

correlate these performance spikes and dips with particular events and occasions, like product

launches, special campaigning or yearly festivals.

Capacity planners should evaluate these statistics on an ongoing basis. Like the weekly and

yearly graphs, daily and hourly graphs also have to be analyzed. For new applications which do

not have any such statistical data, the capacity planner will have to rely upon the suppositions

made by business experts, until such data are recorded.

There will always be unexpected peaks in application demand beyond the expectation

of capacity planner. The goal of capacity planning is not to eliminate the occurrence of such

unexpected peaks. Rather it is about planning for the expected, recognizing the unexpected,

and reacting appropriately to the deviation.


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