[samplers/probability] Implements a traceIdRatio sampler

[yuanyuanzhao3]

Description

Implements a TraceIdRatioBased sampler in go.opentelemetry.io/contrib/samplers/probability/traceidratio that conforms to the OpenTelemetry specification's threshold-based sampling algorithm.

Features

• Threshold-based sampling: Uses the least significant 56 bits of the trace ID (per W3C Trace Context Level 2 Random Trace ID Flag) for deterministic sampling decisions
• Tracestate th handling: Encodes and propagates the sampling threshold in the W3C ot tracestate vendor key for consistent downstream sampling
• Random bit support: Integrates with TraceFlags.IsRandom() and WithRandom() (opentelemetry-go#8012) for proper indication of th value for extrapolated metrics support

Dependencies

This module temporarily uses replace directives to pin to the opentelemetry-go commit that includes IsRandom/WithRandom (opentelemetry-go#8012, merge commit 2ffde5a42). These replaces should be removed once opentelemetry-go releases a version that includes those APIs.

Related

• Part of opentelemetry-go#7928 (Support TraceIdRatioBased Sampler)
• Depends on opentelemetry-go#8012 (trace: add Random Trace ID Flag)

Co-Author

Joshua MacDonald jmacd@users.noreply.github.com

[codecov]

Codecov Report

❌ Patch coverage is 95.41284% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.2%. Comparing base (b24435f) to head (3cd6a7b).

Files with missing lines	Patch %	Lines
samplers/probability/traceidratio/sampler.go	94.6%	2 Missing and 1 partial ⚠️
samplers/probability/traceidratio/version.go	0.0%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff           @@
##            main   #8714    +/-   ##
======================================
  Coverage   82.2%   82.2%            
======================================
  Files        183     186     +3     
  Lines      13812   13921   +109     
======================================
+ Hits       11354   11449    +95     
- Misses      2054    2068    +14     
  Partials     404     404            

Files with missing lines	Coverage Δ
samplers/probability/traceidratio/tracestate.go	100.0% <100.0%> (ø)
samplers/probability/traceidratio/version.go	0.0% <0.0%> (ø)
samplers/probability/traceidratio/sampler.go	94.6% <94.6%> (ø)

... and 2 files with indirect coverage changes

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[yuanyuanzhao3]

@jmacd as FYI.

[jmacd]

Nice! Thank you.

General comments:

• I think this belongs in the core SDK (eventually), as a core part of the OTel tracing specification
• With this PR it is definitely time to remove the older probability sampler.
  #6176

[jmacd]

For the record, this code is identical to https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/1a616d98873ca26622ef6d4698c2e7d1ddd7a25f/pkg/sampling/probability.go#L33, a variation on https://opentelemetry.io/docs/specs/otel/trace/tracestate-probability-sampling/#converting-floating-point-probability-to-threshold-value.

[yuanyuanzhao3]

Nice! Thank you.

General comments:

• I think this belongs in the core SDK (eventually), as a core part of the OTel tracing specification
• With this PR it is definitely time to remove the older probability sampler.
  Deprecate and remove go.opentelemetry.io/contrib/samplers/probability/consistent #6176

I think so as well. I'm under the impression that this is a temporary home while the sampler is being developed and battle-hardened. Eventually it'll graduate to the core SDK.

@dashpole who suggested this place:

It looks like the TraceIDRatioBased sampler is still development stability, right? In that case we will need to add the sampler in a v0.* module. It might need to live in contrib, similar to the minsev logging processor: https://github.com/open-telemetry/opentelemetry-go-contrib/tree/main/processors/minsev.