InfoCenter Home > 6.6.0.12.1: Rating the impact of performance monitoringThis section explains the ratings for the impact costs of counters and instrumentation levels. The following topics are included:
Understanding the impact ratings for data countersBy default, performance data is automatically collected for WebSphere resources and for run-time resources. All data collection affects performance in some way, and the impact on performance varies depending on the counter. The Resource Analyzer represents the overhead cost associated with each counter as a rating of low, medium, or high. If a counter has a low cost rating, its performance cost is minor and usually involves a single addition or subtraction. A counter with a high cost rating has a higher performance impact. A high cost rating usually indicates that several calculations, including multiplication, division, or both, are involved in gathering the data for the counter. For example, collecting the number of times a bean instance is passivated has a low impact on performance. Calculating the average response time on all methods of an enterprise bean's remote interface has a medium impact on performance; calculating the average number of methods being processed concurrently has a high impact. The associated cost rating (low, medium, or high) for each counter is listed in Performance data. Understanding instrumentation levels for data collectionThe resources in a WebSphere administrative domain are instrumented so that statistical data can be collected. Instrumentation refers to the mechanism by which some aspect of the running system is measured (analogous to a meter attached to a resource). Each resource category has an instrumentation level (different from the impact rating for the counters in that category). The instrumentation level determines which counters are available to be collected for that category. The instrumentation level is set through the Monitoring Settings menu option in the Resource Analyzer, or through the Properties dialog box, which is accessed from the WebSphere Administrative Console. See Setting the instrumentation level for information about this task. For example, if a resource category has an instrumentation level setting of low, only counters having a low-impact cost rating are available for selection. If the instrumentation level is set to medium, then counters having low- impact and medium-impact cost ratings are available for selection. Similarly, when the instrumentation level is set to high, all counters with low-, medium-, and high-impact cost ratings are available for selection. An instrumentation level also can be set to maximum, which enables the availability of all counters and, in addition, increases the level of granularity when reporting on enterprise methods. This setting has a higher impact on a system's performance. Conversely, the instrumentation level can be set to none, which disables performance reporting and eliminates any impact of monitoring on system performance. Initially, the instrumentation levels are set to none. When you set an instrumentation level at the root level of the resource, all instances of that resource acquire the same setting. Any individual instance can be selected and separately set to a different instrumentation level. The instrumentation levels rate the approximate performance costs for counters. However, the ratings do not reflect the impact of counters that can become numerous. See Performance data for more information on instrumentation levels and counters for each resource category. Indentifying the instrumentation level represented in the graphic displayThe instrumentation level can be set for each resource category and for each resource instance. The current instrumentation level is represented by a small icon with a dial setting. The meanings of the dial settings are as follows:
See Performance data for more information on instrumentation levels and counters for each resource category. |
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