IBM Tivoli Composite Application Manager for Application Diagnostics, Version 7.1.0.1
Threshold calculation detail
To set parameters that affect the calculation of the automatic response time thresholds, you may need to know the details of this calculation.
ITCAM processes the baselining statistical data and applies the auto threshold parameters in the following way...
- The response time results are sorted into up to 64 "buckets", from zero to the maximum response time encountered for this request.
The buckets do not represent equal time intervals; for response time regions where most of the "hits" fall, the buckets will represent smaller intervals. For example, if the maximum encountered time is 1000 ms but most response times are between 300 and 500 ms, then the first bucket may be 0 to 50 ms, but there may also be buckets representing response times of 305 to 310 ms and 400 to 402 ms. ITCAM distributes the bucket borders so that the largest number of hits in any one bucket will not be more than three times the amount of hits in the smallest bucket.
ITCAM calculates the percentage of the total amount of requests that fall into each response time bucket, and divides it by the time interval width that the bucket represents. This is shown on the Response Times Distribution bar chart in the Request Baseline workspace.
Each bar represents a bucket, and the bar height shows the percentage of the requests in this bucket. All the subsequent calculations are rounded up to buckets.
- ITCAM determines the selection zone, which contains the "typical" response time values. This zone is represented by the bars colored blue on the chart.
ITCAM finds the response time interval (left border L to right border R) where the following statements are true:
- The percentage of hits that fall into this interval is no less than the Auto_Threshold_Percent parameter.
- The spread of the time interval, calculated as (R/L)*100 - 100, is not greater than the Auto_Threshold_Deviation parameter.
The Auto_Threshold_Deviation parameter does not denote the statistical definition of deviation.
If several zones match these criteria, ITCAM will choose the one where the following value is the greatest: S/(R-L), where S is the total number of hits that fell into this zone.
If a zone where both requirements are true cannot be found at all, ITCAM will first determine the interval where the percentage of hits is not less than the Auto_Threshold_Percent parameter while the spread is as little as possible. Then, within this interval, it will find a zone where the spread is not greater than the Auto_Threshold_Deviation parameter and the percentage of hits is as big as possible.
ITCAM will determine the typical nested request times from the nested request times in this zone, shown on the Level2 Delays Distribution chart.
- Finally, ITCAM calculates the thresholds.
The fair threshold is determined using the left and right borders of the selection zone and the Auto_Threshold_Fair_Projection parameter:
F = L + ((R-L) * Auto_Threshold_Fair_Projection / 100)
The bad threshold is calculated in the same way, using the Auto_Threshold_Bad_Projection parameter:
B = L + ((R-L) * Auto_Threshold_Bad_Projection / 100)
Example: the left border of the selection zone may be L=1450 ms, and the right border R=3000 ms. By default, Auto_Threshold_Fair_Projection=150, and Auto_Threshold_Bad_Projection=300. In this case:
- The fair response threshold is...
F = 1450 + ((3000-1450) * 150 / 100) = 3775 ms
- The bad response threshold is...
B = 1450 + ((3000-1450) * 300 / 100) = 6100 ms
Parent topic:
Take Action commands for ITCAM Agent for WebSphere Applications