sampling.md

Sampling

A cloud-scale web application generates a very large number of traces. You can set up one or more sampling strategies in your application to reduce the volume of trace data that it sends to Wavefront.

You set up a sampling strategy by configuring the WavefrontTracer with an implementation of the Sampler interface.

For example, suppose you want to allow approximately 1 out of every 5 traces. The following snippet shows how to configure a WavefrontTracer with a RateSampler:

// Create a RateSampler with a rate of 20%
sampler := tracer.RateSampler{Rate: 20}

// Create the WavefrontTracer
tracer.New(reporter, WithSampler(sampler))

Supported Sampling Strategies

The following table lists the supported sampling strategies:

Sampler	Description
DurationSampler	Allows a span if its duration exceeds a specified threshold. Specify the duration threshold as a time.Duration number of milliseconds.
RateSampler	Allows a specified probabilistic rate of traces to be reported. Specify the rate of allowed traces as a unint64 number between 0 and 100.

Note: Regardless of the sampling strategy, the WavefrontTracer:

• Allows all error spans (error=true span tag).
• Allows all spans that have a sampling priority greater than 0 (sampling.priority span tag).
• Includes all spans in the RED metrics that are automatically collected and reported.

Using Multiple Sampling Strategies

You can configure a WavefrontTracer with multiple sampling strategies. In this case, the WavefrontTracer allows a span if any of the samplers decide to allow it.

For instance, suppose you want to report approximately 10% of traces but you also don't want to lose any spans that are over 60 seconds long. The following code snippet shows how to configure a WavefrontTracer with a RateSampler and a DurationSampler:

// Create and configure the RateSampler and DurationSampler
rateSampler := tracer.RateSampler{Rate: 10}
durationSampler := tracer.DurationSampler{Duration: 60 * time.Second}

// Create the WavefrontTracer
tracer.New(reporter, WithSampler(rateSampler), WithSampler(durationSampler))