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IBM Tivoli Monitoring > Version 6.3 > User's Guides > Agent Builder User's Guide > Edit data source and attribute properties > Create derived attributes IBM Tivoli Monitoring, Version 6.3
Interval specific calculations
You can choose Interval specific calculations when you define a derived attribute that is based on the rate or delta functions.
You select Interval specific calculations on the Derived Attribute Details tab of the Attribute Information page. See Create derived attributes.
When you use the Interval specific calculations selection, it is important to understand the concept of a delta or difference between attribute values. The delta is the difference between the most recent value of the attribute and a previous value of the attribute. The delta is returned directly by the delta function and is used by the rate function to calculate a result.
The delta or rate function must always have the last function as its only argument. The last function specifies which values of an attribute are used to determine the delta. If Interval specific calculations is not selected, the previous value that is used is always the second-most-recent value. If Interval specific calculations is selected, the previous value that is used is the value whose age (relative to the most recent value) is equal to the collection interval of the requester.
For example, suppose CDP_DP_REFRESH_INTERVAL is set to 120 seconds and attribute A has the following sampled values:
Time Sampled value current 2800 2 minutes (120 seconds) ago 2600 4 minutes (240 seconds) ago 2499 6 minutes (360 seconds) ago 1500 8 minutes (480 seconds) ago 1200 10 minutes (600 seconds) ago 1000
When Interval specific calculations is not selected, the delta function always returns 200, the difference between the two most recent values, 2800 - 2600. The same value is returned whether the value is displayed on the Tivoli Enterprise Portal, used in a situation, or a historical collection.
When Interval specific calculations is selected, the delta function returns a value that depends on the collection interval of the requester.
If a derived attribute with the delta function is used in a situation with a 4-minute collection interval, the value that is returned by the delta function is 301, the difference between the most recent value and the value obtained 4 minutes before that, 2800 - 2499.
If a derived attribute with the rate function is used in a situation with a 10-minute (600-second) collection interval, the value that is returned by the rate function is 3, the difference between the most recent value and the value obtained 10 minutes before that, divided by the number of seconds in the interval (2800 - 1000) / 600.
The Tivoli Enterprise Portal has no inherent collection interval, so delta and rate calculations for Tivoli Enterprise Portal requests always use the most recent and second most recent attribute values, the same result whether Interval specific calculations is selected or not.
For delta or rate to work correctly with Interval specific calculations,
- The agent must collect data periodically in the background, and not on demand (CDP_DP_THREAD_POOL_SIZE must be greater than 0).
- Every situation or historical collection interval in which the attribute is used must be a multiple of the background refresh interval (CDP_DP_REFRESH_INTERVAL).
- The count (the second argument of the last function) must be large enough to accommodate the largest collection interval from a situation or historical collection. For example, if the agent must support 10-minute (600 second) historical collection and CDP_DP_REFRESH_INTERVAL is 120 seconds, the count must be at least 6, 1+(600 / 120). A count value of 6 ensures that the last function returns the newest sample and samples up to 600 seconds old.
If these conditions are not met, input values are likely invalid and a result of 0 is returned.
Parent topic:
Create derived attributesRelated tasks:
Create derived attributesRelated reference:
Environment variables
Formula operators and functions