[Feature]: Tail sampling

[pcan]

Related Problems?

No response

Describe the solution you'd like:

We are currently using the @microlabs/otel-cf-workers library to enable open telemetry our CloudFlare workers. The configuration allows to specify both head sampling and tail sampling, which gives greater flexibility to filter traces based on their content after the Spans have been generated:

const otelConfig = {
  exporter: {
    url: "http://localhost:12345/v1/traces"
  },
  sampling: {
    headSampler: { ratio: 0.01 },  // this allows to specify head sampling rule
    tailSampler: ({ localRootSpan, spans }) =>  // here we override the final decision
      localRootSpan.status.code === SpanStatusCode.ERROR ||
      localRootSpan.spanContext().traceFlags === TraceFlags.SAMPLED ||
      spans.some((s) => s.status.code === SpanStatusCode.ERROR),
  }
};

Would it be possible to achieve the same functionality with opentelemetry-rust?

Considered Alternatives

I was looking into customizing the SpanExporter, but its implementation seems to be quite locked down. In theory, based on this comment it should be possible, but I could not find any working example.

Additional Context

No response

[fw42]

@pcan: Did you find a solution? Having the same problem

[pcan]

@fw42 not at the moment, we deprioritized the related work for the time being, but it'd be still useful to have this feature.