[−][src]Module opentelemetry::api::trace::sampler

OpenTelemetry Sampler Interface

Sampling

Sampling is a mechanism to control the noise and overhead introduced by OpenTelemetry by reducing the number of samples of traces collected and sent to the backend.

Sampling may be implemented on different stages of a trace collection. OpenTelemetry API defines a Sampler interface that can be used at instrumentation points by libraries to check the sampling SamplingDecision early and optimize the amount of telemetry that needs to be collected.

All other sampling algorithms may be implemented on SDK layer in exporters, or even out of process in Agent or Collector.

The OpenTelemetry API has two properties responsible for the data collection:

  • is_recording method on a Span. If true the current Span records tracing events (attributes, events, status, etc.), otherwise all tracing events are dropped. Users can use this property to determine if expensive trace events can be avoided. SpanProcessors will receive all spans with this flag set. However, SpanExporters will not receive them unless the Sampled flag was set.
  • Sampled flag in trace_flags on SpanContext. This flag is propagated via the SpanContext to child Spans. For more details see the W3C specification. This flag indicates that the Span has been sampled and will be exported. SpanProcessors and SpanExporters will receive spans with the Sampled flag set for processing.

The flag combination SampledFlag == false and is_recording == truemeans that the currentSpandoes record information, but most likely the childSpan` will not.

The flag combination SampledFlag == true and IsRecording == false could cause gaps in the distributed trace, and because of this OpenTelemetry API MUST NOT allow this combination.

Structs

SamplingResult

The result of sampling logic for a given Span.

Enums

SamplingDecision

Decision about whether or not to sample

Traits

Sampler

The Sampler interface allows implementations to provide samplers which will return a sampling SamplingResult based on information that is typically available just before the Span was created.