Sampling IntervalSampling IntervalThe Sampling interval is the frequency of data collection.
For Event-based sampling (EBS), the Sampling interval is used to calculate the target number of samples and the Sample After value. If you change the value of Duration or Sample Interval, the Sample After value is updated automatically. Make sure to enable the Calibrate Sample After option in order to determine the correct Sampling interval. To calculate the average number of samples collected per second per event, use the following formula:
Number of samples (samples) = Duration (sec) / Sampling Interval (sec)/ number of processors
For example:
Duration = 10 seconds
Sampling interval = 1 millisecond
Number of processors = 1
The number of samples collected per second is calculated as follows:
Number of samples = (10 (sec) / 0.001(sec) )/1= 10000 samples
This number of samples collected per second is multiplied by Duration to get the target number of samples that are collected for an event in an Activity run. The Sample After value is calculated based on the target number of samples for an event.
To determine an appropriate Sampling interval, consider the Duration of the collection, the speed of your processors, and the amount of software activity. For instance, if the Duration of sampling time is more than 10 minutes, consider increasing the Sampling interval to 50 milliseconds. This reduces the number of interrupts and the number of samples collected and written to disk. The smaller the Sampling interval, the larger the number of samples collected and written to disk.
From the Configure Sampling dialog box, select the General panel.
Type in the value to specify the Sampling Interval text box.
use -si | -sampling-interval <interval in milliseconds>.
Command-line example:
>vtl activity -d 15 -c sampling -o "-si 4" run
This example creates and runs an Activity with the sampling collector for 15 seconds using a sampling interval of 4ms. The sampling collector uses the event-based sampling mechanism and collects samples for the clockticks event. The calibration run will calculate the Sample After value for the event using a 4ms sampling interval. During the sampling run the sampling collector will use the calculated Sample After value. After the clockticks event occurs, a Sample After value number of times a sample will be taken. See the Calibration topic for more information.
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