Sampler that passes spans based on name prefix

[breedx-splk]

Users have asked for a way to ensure that their manually created spans are never sampled out while still allowing the rest of instrumentation to sample normally. One approach I'm suggesting here is to create a new sampler that can be preconfigured with a set of span name prefixes to always include. That is, if a span name starts with one of the prefixes, it always passes. If it does not, then this sampler will delegate to another sampler.

Might be a little tricky to choose a name for this. Something like NamePrefixedForceInclusionSampler.

[jkwatson]

The opposite of this would also be super useful... To remove spans based on name.

[anuraaga]

If it's about manual sampling instead of relying on name, I think context attribute to force sampling can work and more flexible.

[iNikem]

One more option to always include manual spans is to use InstrumentationLibrary.Name: if it does not start with io.opentelemetry, then return RECORD

[jkwatson]

One more option to always include manual spans is to use InstrumentationLibrary.Name: if it does not start with io.opentelemetry, then return RECORD

how would you implement that with a Sampler? Samplers don't have access to the Tracer implementation being used to create the span.

[breedx-splk]

If it's about manual sampling instead of relying on name, I think context attribute to force sampling can work and more flexible.

The usage then looks something like this?

Context context = Context.current().withValue(MANUALLY_CONTROLLED_SAMPLER, NEVER_DROP);
Span span = tracer.spanBuilder("xxx").setParent(context).startSpan();
[...]

I agree, it's more explicit that way and requires less fiddling with the sampler and specifying some names.

There's probably opportunity to make that even more convenient with helpers on the SpanBuilder too I suppose.

[iNikem]

One more option to always include manual spans is to use InstrumentationLibrary.Name: if it does not start with io.opentelemetry, then return RECORD

how would you implement that with a Sampler? Samplers don't have access to the Tracer implementation being used to create the span.

They are going to, hopefully: open-telemetry/opentelemetry-specification#1588