/// <summary>
/// Callback for sampling percentage evaluation timer.
/// </summary>
/// <param name="state">Timer state.</param>
private void EstimateSamplingPercentage(object state)
{
// get observed after-sampling eps
double observedEps = this.itemCount.StartNewInterval() / this.evaluationInterval.TotalSeconds;
// we see events post sampling, so get pre-sampling eps
double beforeSamplingEps = observedEps * this.currenSamplingRate;
// caclulate suggested sampling rate
int suggestedSamplingRate = (int)Math.Ceiling(beforeSamplingEps / this.settings.EffectiveMaxTelemetryItemsPerSecond);
// adjust suggested rate so that it fits between min and max configured
if (suggestedSamplingRate > this.settings.EffectiveMaxSamplingRate)
{
suggestedSamplingRate = this.settings.EffectiveMaxSamplingRate;
}
if (suggestedSamplingRate < this.settings.EffectiveMinSamplingRate)
{
suggestedSamplingRate = this.settings.EffectiveMinSamplingRate;
}
// see if evaluation interval was changed and apply change
if (this.evaluationInterval != this.settings.EffectiveEvaluationInterval)
{
this.evaluationInterval = this.settings.EffectiveEvaluationInterval;
this.evaluationTimer.Change(this.evaluationInterval, this.evaluationInterval);
}
// check to see if sampling rate needs changes
bool samplingPercentageChangeNeeded = suggestedSamplingRate != this.currenSamplingRate;
if (samplingPercentageChangeNeeded)
{
// check to see if enough time passed since last sampling % change
if ((DateTimeOffset.UtcNow - this.samplingPercentageLastChangeDateTime) <
(suggestedSamplingRate > this.currenSamplingRate
? this.settings.EffectiveSamplingPercentageDecreaseTimeout
: this.settings.EffectiveSamplingPercentageIncreaseTimeout))
{
samplingPercentageChangeNeeded = false;
}
}
if (samplingPercentageChangeNeeded)
{
// apply sampling perfcentage change
this.samplingPercentageLastChangeDateTime = DateTimeOffset.UtcNow;
this.currenSamplingRate = suggestedSamplingRate;
}
if (samplingPercentageChangeNeeded ||
MovingAverageCoefficientChanged(this.itemCount.Coefficient, this.settings.EffectiveMovingAverageRatio))
{
// since we're observing event count post sampling and we're about
// to change sampling rate or change coefficient, reset counter
this.itemCount = new ExponentialMovingAverageCounter(this.settings.EffectiveMovingAverageRatio);
}
}
/// <summary>
/// Initializes a new instance of the <see cref="SamplingPercentageEstimatorTelemetryProcessor"/> class.
/// <param name="settings">Dynamic sampling estimator settings.</param>
/// <param name="callback">Callback to invoke every time sampling percentage is evaluated.</param>
/// <param name="next">Next TelemetryProcessor in call chain.</param>
/// </summary>
public AdaptiveSampler(SamplingPercentageEstimatorSettings settings)
{
if (settings == null)
{
throw new ArgumentNullException("settings");
}
this.settings = settings;
this.currenSamplingRate = settings.EffectiveInitialSamplingRate;
this.itemCount = new ExponentialMovingAverageCounter(settings.EffectiveMovingAverageRatio);
this.samplingPercentageLastChangeDateTime = DateTimeOffset.UtcNow;
// set evaluation interval to default value if it is negative or zero
this.evaluationInterval = this.settings.EffectiveEvaluationInterval;
// set up timer to run math to estimate sampling percentage
this.evaluationTimer = new Timer(
this.EstimateSamplingPercentage,
null,
this.evaluationInterval,
this.evaluationInterval);
}
