When ExportUnsampledSpans is set to true, will the spans exported to collector using OTLP gRPC contain trace flags?

[wdengw]

Issue #6057 implemented ExportUnsampledSpans flag, setting it to true will export all spans to collector no matter a span is sampled or not. This is great! we are looking for this feature. A question regarding this feature is that, will the span data exported contains TraceFlag information for collector to find out whether a received span is sampled or not? @HaloFour and @jack-berg

[trask]

yes, they should be available via https://github.com/open-telemetry/opentelemetry-proto/blob/a8f08fc49d60538f97ffabcc7feac92f832976dd/opentelemetry/proto/trace/v1/trace.proto#L112-L133

[wdengw]

@trask Thank you! This is great! Now trace proto has a field to record the TraceFlags.

One follow up question regarding the implementation of #6057: Should the configuration option of exportUnsampledSpans that is added to BatchSpanProcessor and SimpleSpanProcessor be also added to AlwaysOffSampler for it to return SamplingResult.recordOnly() when exportUnsampledSpans is set to true.

[trask]

Should the configuration option of exportUnsampledSpans that is added to BatchSpanProcessor and SimpleSpanProcessor be also added to AlwaysOffSampler

I'm not sure, since the AlwaysOffSampler is defined in the specification: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk.md#alwaysoff

are you able to create your own sampler and use that?

[wdengw]

To make it work for now. we created a RecordOnlySampler that returns recordOnly Sampling result. We use it to replace AlwaysOffSampler when we configure the TraceProvider when exportUnsampledSpans set to true.

[wdengw]

Here is an enhancement suggestion I filed sometime back: open-telemetry/opentelemetry-specification#2986.