Tool Mentor: Planning a Performance Test
Purpose
This tool mentor describes how to plan a performance test that will be run on Rational LoadTest.
Related Rational Unified Process activities:
- Section "Workload Analysis" of Activity: Design Test
Also see the following pages for additional related information:
Overview
You can use LoadTest to test the performance of a sever by emulating many virtual users. The objective is to find out how the system performs under the load.
Because performance is subjective, when planning performance tests, you need to put some thought into what constitutes acceptable performance. Some of the performance questions you might want to answer are:
- How many virtual users can the server support under normal conditions?
- Are there any situations where server performance degrades suddenly under normal conditions?
- How does the system perform when you exceed the normal conditions? In a worse-case scenario, does the system degrade gracefully, or does it break down completely?
- How does the system perform under varying hardware configurations?
When planning performance tests, keep in mind the objectives of the test. You want to find out how quickly the systems performs what it is designed to do. You want to focus on how the system behaves when executing actual business operations. You will model an actual workload, which is an approximation of real-world environment you are trying to emulate. You can use data during the test to stress the capacity of the system.
To plan a performance test:
- Define your pass and fail criteria.
- Identify the hardware and software that you will test.
- Perform other planning tasks.
1. Define your pass and fail criteria. 
Because performance can be subjective, it is essential that you not only identify the features to be tested, but that you also determine the criteria that will determine whether the performance passes. If you make this determination ahead of time during the planning stages, you can then look at your results against these expectations, and make an assessment of whether the system passes or fails.
The pass criteria will often involve a range of acceptable response times. For example, you may define an acceptable response time as: at 100 users, 90% of all transactions have an average response time of 5 seconds or less, with no response time exceeding 20 seconds; at 500 users, 80% of all transactions have an average response time of 10 seconds or less, with no response time exceeding 45 seconds.
2. Identify the hardware and software that you
will test.
When planning a performance test, you need to determine the hardware and software that your test requires. For example:
- Server computers: database severs, Web servers, other server systems
- Client computers: Windows computers, network computers, Macintosh or UNIX workstations
- Databases that will be accessed
- Applications that will be running
In addition, you should think about the following parameters for your tests:
- How large should the test databases and other test files be in order to accurately represent the real workload?
- How should the data be distributed across the system-under-test in order to prevent I/O bottlenecks?
- If you are testing a database, how should the key database parameters be set?
3. Perform other planning tasks.
Other things you could take into consideration when planning performance
tests are listed below. These topics are all covered in Chapter 2 of the Using
Rational LoadTest manual, which can be found on the documentation CD.
- Designing a realistic workload
- Designing performance tests
- Planning virtual user scripts
- Setting virtual user recording options
- Modifying virtual user scripts
- Correcting errors in virtual user scripts
- Analyzing performance results
