Enterprise Library Test Guide - Willy .Net

Testing for Performance and Scalability 169
Defining Performance Criteria
The most common approach to determining an application’s performance is to measure
its response times and the resources it uses against criteria, such as the application’s
budgets for resources, its business needs, and its service level agreements.
However, it is not always possible to use these criteria with Enterprise Library,
treated as a whole. The reasons for this are:
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There is no single application that encompasses all the application blocks.
Different applications require different resources.
Different applications have different goals.
Because the application blocks cannot be tested in the context of a specific application,
another approach is to measure an application block’s performance goals
against a baseline. This is the approach used with Enterprise Library. The baselines
are the .NET Framework and Enterprise Library 1.1. In this case, an example of a
performance goal may be that an Enterprise Library method should have less than a
15 percent overhead when compared to the overhead of the equivalent .NET Framework
method.
For example, the cost of adding an item to the ASP.NET cache serves as a baseline
measurement for the Caching Application Block’s equivalent Add method. By
comparing the two costs, the overhead of the Enterprise Library application block
becomes apparent.
Measurements of the performance criteria are collected with the Windows Performance
Monitor (Perfmon.exe). Here is the complete list of performance criteria for
Enterprise Library–January 2006:
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Overhead cost
Initialization cost
Consistency
Availability
The next sections discuss these subjects.
Overhead Cost
The overhead cost is expressed as a percentage. It is the difference between the response
time of an application block (or one of its system resources) when it performs
a function and the response time of the .NET Framework and Enterprise Library 1.1
when it performs the same function. The overhead cost is expressed as a percentage
of total transactions (this is also termed “total hits” for Web applications) and as a
percentage of transactions per second. The next sections describe the calculations for
determining the overhead costs.