Current Time Range Charts Custom Time Range Charts

15-8 Configuring and Using the Diagnostics Framework for Oracle WebLogic Server

15.4 Understanding How Metrics Are Collected and Presented

As mentioned in Section 15.2, Scope of the Diagnostic Information Displayed, the Monitoring Dashboard displays metrics from two sources: ■ Real-time, polled metric values that are obtained at regular intervals from running WebLogic Server instances and returned to the Monitoring Dashboard. ■ Metrics collected by the Harvester and placed into the Archive. To view real-time, polled metrics in the Monitoring Dashboard, it is not necessary to configure the Harvester. When a view is started with charts that contain one or more real-time, polled metrics, the runtime MBean instances corresponding to those metrics are polled at each configured interval, and the requested metric values are returned to the Monitoring Dashboard. A polled metric is stored only once in the Monitoring Dashboard, even if that metric has been added to multiple charts or multiple views. The runtime MBean instance corresponding to that metric is also polled only once at each interval, regardless of the number of charts or views in which its metric values are displayed. So when an updated value for a metric arrives in the Monitoring Dashboard, all charts containing that metric are updated simultaneously. This enables the Monitoring Dashboard to minimize the performance overhead on your system and maximize its overall efficiency. To be able to view collected metrics, you must first configure the Harvester to collect the data you want to monitor and have it available in the Archive. In a view with one or more custom time range charts containing collected metrics, the values for those metrics that correspond to the specific custom time ranges are fetched once from the Archive and displayed in those charts. Note that collected metrics data is also available for programmatic access, and it is written to a standard log, HarvestedDataArchive, which you can view using the standard Administration Console as well as the Monitoring Dashboard. For information about configuring the Harvester to collect metrics, see Chapter 7, Configuring the Harvester for Metric Collection.

15.4.1 About Metrics and Chart Types

The way in which the Monitoring Dashboard presents metrics depends upon the chart in which they are displayed. After you add a chart to a view, you can use the Chart Properties dialog box to specify either of the following time ranges: ■ Current ■ Custom The following sections provide key information about how metrics are presented in each chart type.

15.4.1.1 Current Time Range Charts

This is the default time range for charts in the Monitoring Dashboard. Use this time range for displaying real-time, polled metrics, which can be displayed only in current time range charts. These charts are updated at regular intervals, which by default is every 20 seconds. The sample interval can be customized in the Dashboard Preferences dialog box. When you add a metric to a current time range chart, the Monitoring Dashboard fetches a small number of historical values for that metric from the Archive, if they are available. Note the following about metric values obtained from the Archive for current time range charts: Using the Monitoring Dashboard 15-9 ■ The number of values fetched is derived from the amount of time over which the stored samples can range, in which the sample interval is multiplied by the maximum samples for the chart. The default sampling interval is 20 seconds and the default sample maximum is 100, which yields a time range of 2000 seconds, or approximately 33.3 minutes. ■ If the sampling interval used by the Harvester is different from the one configured for the Monitoring Dashboard, some distortion may be evident in the graphing of that metric.

15.4.1.2 Custom Time Range Charts

Charts configured with a custom time range display collected metrics only. When you specify a custom time range for a chart and add a collected metric, the Monitoring Dashboard fetches the metric’s values from the Archive that match the specified time range. These charts are static: once the Monitoring Dashboard displays collected metrics in a custom time range chart, the values of those metrics are never updated. Note the following: ■ Custom time range charts never include real-time, polled metric values. ■ As a convenience for creating custom time range charts, the Metric Browser includes a button labeled Collected Metrics Only. When you select this button, the Metric Browser displays only collected metrics.

15.4.2 Sequence in which Metrics Data is Displayed