Create probabilistic sampler

[slashmo]

Still a draft because of missing documentation and the dependency on swift-otel/swift-w3c-trace-context#11.

[ktoso]

Is this how other tracers implement this? A bit sneaky but looks good overall :)

[slashmo]

Is this how other tracers implement this? A bit sneaky but looks good overall :)
@ktoso

“Some tracer implementations make use of the fact that in many tracing systems, the trace ID itself is a randomly generated number and can be used to avoid making a second call to the random number generator, in order to reduce the overhead:”

Excerpt From: “Mastering Distributed Tracing”. Apple Books.

It's what get's recommended in the Mastering Distributed Tracing book and is also being used in the Java Jaeger client and OpenTelemetry Swift.

[ktoso]

Yeah, okey then.

I know some tracers use parts of that number to hardcode information (I think xray does, not sure if lower or higher) but seems jaeger doesn't so it's a full nice random number :)

LGTM