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How are 95th Percentiles calculated in CA Performance Management (CAPM)

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Article ID: 42216

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Updated On:

Products

CA Infrastructure Management CA Performance Management - Usage and Administration DX NetOps

Issue/Introduction

How 95th Percentiles are calculated in CA Performance Management.

Environment

Dx NetOps Performance Management any version

Resolution

A percentile is the value of a variable below which a certain percent of observations fall. For example, the 95th percentile is the value (or score) below which 95 percent of the observations are found. Percentiles are calculated for rollups, dashboards, and report generation purposes.

Percentile monitoring is useful in measuring throughput data. This statistic more accurately reflects the required capacity of the monitored link for applications that are bandwidth sensitive. The 95th percentile says that 95 percent of the time, the bandwidth usage is below this amount. The remaining 5 percent of the time, the bandwidth usage is above that amount.

Metric values are aggregated during rollups.

By default, CA Performance Management calculates the 95th percentile for some metrics. Metric families can include up to two more configurable percentile calculations.

Metric Property

Default

Values

Percentile

Disabled or 95

0 or 95

Percentile2

Disabled

0-99

Percentile3

Disabled

0-99

A value of 0 disables the percentile calculation.

Changes to these properties generate Administration events. After you update the metric family, the percentile data is available for reporting within several poll cycles. For trend views, changes cause a gap in the trend line. For table views, changes affect the value of the percentile for time ranges when the change occurred. For example, in a daily time range, the value is inaccurate for one day.

Tip: When you disable a percentile, modify views that include the percentile to avoid an error in the view.

Important! Calculate only percentiles that you need. Each percentile that you calculate might significantly affect system performance. For more information, see the CA Performance Management Sizing Tool.

For more information, see TechDocs : DX NetOps 21.2 CAPM : Metric Family XML StructureYou can manually edit percentiles using the CA Performance Center user interface. For more information, see Edit a Metric.

Three percentile values appear in the Metric Families table under the Monitoring Configuration menu for a Data Aggregator. A dash in the Percentiles column indicates that all three percentile values are equal to zero. For more information, see View Metric Families.

Percentile Calculations

Percentile calculations use the Microsoft Excel method.

Hourly and daily rollups store the 95% (plus upto 2 others) for the item's hour or day. 
Hourly uses the Polled data for the hour to calculate 95%.  Daily uses Polled data for the day to calculate 95%.   
Weekly rollups are based on daily rollup.  So weekly 95% would be calculated using the 7 days of daily values.

Percentiles are calculated for all items in the metric family it's defined in, for the metric it's defined on.
So 95% interface utilization would be calculated for all interfaces off utilization values stored in Polled table for hourly, daily.  And off utilization values stored in daily rollup table.