For load testing tools and how to perform the load testing, see 17.3, Tools of the trade.
If you are using the Runtime Performance Advisor in a test environment, or doing any other tuning for performance, simulate a realistic production load for your application. The application should run this load without errors. This simulation includes the number of concurrent users typical for peak periods, and drives system resources, such as CPU and memory to the levels expected during peak production periods. The Performance Advisor can provide some type of advice only when the CPU utilization exceeds a sufficiently high level. For example, advice on thread pool size is only issued if there is a problem with it (which can usually only be detected when the system is under load). Other types of advice, however, are always issued, for example advice related to the Prepared statement cache or the Servlet Session module.
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| Select Warning in the Administrative Console under Troubleshooting -> Runtime Messages or look at the SystemOut.log file, located in the <install_root\logs\servername> directory to view tuning advice. Some messages are not issued immediately.
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| Change your appserver configuration based on the received advice.
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Important: As with any analysis and tuning, make sure that only one parameter is changed, and then the results monitored. This provides an effective method of backing out of the change if it proves detrimental to the environment. Also, making multiple changes could result in undesired results, because many options are dependent on other settings.
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Although the Performance Advisors attempt to distinguish between loaded and idle conditions, misleading advice might be issued if the advisor is enabled while the system is ramping up or down. This result is especially likely when running short tests. Although the advice helps in most configurations, there might be situations where the advice hinders performance. Due to these conditions, advice is not guaranteed. Therefore, test the environment with the updated configuration to ensure it functions and performs as expected.
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Tips for using the Runtime Performance Advisor:
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| Enable PMI in the appserver and in the Node Agent if running ND.
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| Be sure to configure the correct number of processors.
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Ensure the application runs without exceptions/errors.
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Runtime Performance Advisor only provides advice when CPU utilization is high.
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| Once production load level is reached, enable the Runtime Performance Advisor.
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| Apply advice, restart the appserver, and re-test.
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| More details can be found in the WebSphere InfoCenter section "Using the Runtime Performance Advisor".
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