4.4 Advance detection of an excess beyond the threshold by trend monitoring
Trend monitoring calculates trends in the performance trends of monitored services and detects in advance possible overages of a service performance threshold. Trend monitoring monitors each monitoring item.
A trend is an approximated straight line obtained from current service performance. An approximated straight line is calculated on the basis of the past N hours of service performance. If this approximated straight line exceeds the threshold within N hours from the present time, this event is detected as a warning sign of a potential service performance error. The value of N is specified in the Settings window.
For details about how to specify numeric values in the Settings window, see 4.6.2 Setting up the monitoring items for service performance.
The following shows an example in which an overage of a threshold is detected ahead of time by trend monitoring.
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![[Figure]](GRAPHICS/F0000028.GIF)
This example monitors average response time. The trend is calculated from the past N hours of service performance. A warning sign is detected if the service performance is predicted to exceed the threshold within the next N hours.
To obtain a trend for predicting an overage of a threshold within N hours, N hours' worth of service performance is required. This reduces the error associated with a long period of trend monitoring. To predict an overage of a threshold during the next hour, one hour's worth of service performance is required.
The approximated straight line is updated every 60 seconds and each time this occurs a check is performed to see if an overage of the threshold might occur. If an overage of the threshold is predicted, a warning is displayed in the window.
The following shows an example of a warning displayed in the window.
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![[Figure]](GRAPHICS/F0000039.GIF)
The information displayed in the window includes a warning icon, the detection date and time, the time at which service performance is predicted to exceed the threshold, the name of the service group subject to the warning, and the service name. If the trend keeps exceeding the threshold, a warning is displayed only the first time the trend is detected. You can view the service performance leading up to and following the point of the warning as a graph.
The following shows an example of a graph that is displayed.
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![[Figure]](GRAPHICS/F0000013.GIF)
In the graph, a warning icon is displayed indicating the time when a value that exceeded the trend threshold was detected. Also, a yellow band is displayed indicating the time when service performance is predicted to exceed the threshold and the time when a value that exceeded the trend threshold was detected.
To run trend monitoring, you must specify the following items in the Settings window:
Threshold
Reference time for calculating trends
- Threshold
Specifies the reference threshold that is to be used to determine the status of the monitored service.
- Reference time for calculating trends
Specifies N hours as the reference time for calculating trends. N hours are used as follows:
A trend is calculated on the basis of the past N hours of service performance.
A warning sign is detected if an overage of a threshold is predicted to occur within N hours from the present time.
For details about monitor items, see 4.2 Monitoring methods and monitor items of SLM. Note, however, that trend monitoring cannot be used for monitoring the error rate.
For details about trend monitoring, see the description about trend monitoring in the manual JP1/Service Level Management.