Remove SpanId from Sampler input

[reyang]

Discussed during the 05/26/2020 specification SIG meeting.

Do we want SpanId as an input to a sampler?

• As of now ID of to be created span is required: https:/open-telemetry/opentelemetry-specification/blob/5b78ee1adf437bb6c151d8992129f22970a96677/specification/trace/sdk.md#sampler
  • Asked around and nobody recalled why we had SpanID in the first place, and there is no outstanding use case.
  • Agreed to remove it from the spec.
  • Resolution: @reyang will propose removing SpanID from sampling, to reduce overhead.
• History sampling document #81
• Discussion Added sampler to Activity - v1 opentelemetry-dotnet#683 (comment)
• Related & new: Sampling decison is too late to gain much performance #620 Sampling decison is too late to gain much performance

[Oberon00]

You could also add wording to recommend not generating the span IDs before calling the sampler, but maybe that's obvious now. That would be something that should be added to the auto-generated ticket/TODO-list-at-release 😄

[carlosalberto]

cc @yurishkuro

[carlosalberto]

Merged as we had enough approvals.