trace: add Random Trace ID Flag by yuanyuanzhao3 · Pull Request #8012 · open-telemetry/opentelemetry-go

yuanyuanzhao3 · 2026-03-06T18:45:45Z

Summary

Adds API support for the W3C tracecontext random flag on TraceFlags and SpanContext in go.opentelemetry.io/otel/trace:

TraceFlags.IsRandom() — reports whether the random bit is set
TraceFlags.WithRandom(bool) — sets or clears the random bit in a copy of the flags
SpanContext.IsRandom() — reports whether the random bit is set in the span context's trace flags

These mirror the existing IsSampled / WithSampled pattern.

Motivation

The W3C Trace Context spec defines a random bit in trace flags to indicate probabilistic sampling. This is required for TraceIdRatioBased sampler support, where the random bit is set when a trace is probabilistically sampled and is used for extrapolated span metrics.

Co-Author

Joshua MacDonald jmacd@users.noreply.github.com

Co-authored-by: Joshua MacDonald <jmacd@users.noreply.github.com>

codecov · 2026-03-06T18:56:48Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.6%. Comparing base (9c5a5df) to head (30dc8a0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #8012   +/-   ##
=====================================
  Coverage   81.5%   81.6%           
=====================================
  Files        304     304           
  Lines      23444   23452    +8     
=====================================
+ Hits       19130   19137    +7     
- Misses      3930    3931    +1     
  Partials     384     384

Files with missing lines	Coverage Δ
trace/trace.go	`98.2% <100.0%> (+<0.1%)`	⬆️

... and 2 files with indirect coverage changes

🚀 New features to boost your workflow:

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Added new features for W3C tracecontext random flag support in TraceFlags and SpanContext.

yuanyuanzhao3 · 2026-03-06T21:12:27Z

FYI, @jmacd

dashpole · 2026-03-09T15:41:26Z

Overall, this makes sense to me. Can you share more details about how you will use them? What are you trying to do that needs these?

yuanyuanzhao3 · 2026-03-09T19:16:29Z

Overall, this makes sense to me. Can you share more details about how you will use them? What are you trying to do that needs these?

done. please take a look there.

yuanyuanzhao3 · 2026-03-11T21:27:41Z

This is ready to merge whenever the maintainers are ready. Do we need a second approval? @MrAlias or @dmathieu FYI just in case.

dmathieu · 2026-03-12T08:13:42Z

We do need a second approval.

CHANGELOG.md

trace/trace.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

yuanyuanzhao3 · 2026-03-12T17:14:22Z

From the contribution guideline, it looks like this is ready to be merged by a maintainer? If so, can someone help to merge? Or let me know what else is needed. Thanks.

Release issue: #8127 ## Added - Add `IsRandom` and `WithRandom` on `TraceFlags`, and `IsRandom` on `SpanContext` in `go.opentelemetry.io/otel/trace` for [W3C Trace Context Level 2 Random Trace ID Flag](https://www.w3.org/TR/trace-context-2/#random-trace-id-flag) support. (#8012) - Add service detection with `WithService` in `go.opentelemetry.io/otel/sdk/resource`. (#7642) - Add `DefaultWithContext` and `EnvironmentWithContext` in `go.opentelemetry.io/otel/sdk/resource` to support plumbing `context.Context` through default and environment detectors. (#8051) - Support attributes with empty value (`attribute.EMPTY`) in `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`. (#8038) - Support attributes with empty value (`attribute.EMPTY`) in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`. (#8038) - Support attributes with empty value (`attribute.EMPTY`) in `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc`. (#8038) - Support attributes with empty value (`attribute.EMPTY`) in `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp`. (#8038) - Support attributes with empty value (`attribute.EMPTY`) in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#8038) - Support attributes with empty value (`attribute.EMPTY`) in `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#8038) - Support attributes with empty value (`attribute.EMPTY`) in `go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest`. (#8038) - Add support for per-series start time tracking for cumulative metrics in `go.opentelemetry.io/otel/sdk/metric`. Set `OTEL_GO_X_PER_SERIES_START_TIMESTAMPS=true` to enable. (#8060) - Add `WithCardinalityLimitSelector` for metric reader for configuring cardinality limits specific to the instrument kind. (#7855) ## Changed - Introduce the `EMPTY` Type in `go.opentelemetry.io/otel/attribute` to reflect that an empty value is now a valid value, with `INVALID` remaining as a deprecated alias of `EMPTY`. (#8038) - Refactor slice handling in `go.opentelemetry.io/otel/attribute` to optimize short slice values with fixed-size fast paths. (#8039) - Improve performance of span metric recording in `go.opentelemetry.io/otel/sdk/trace` by returning early if self-observability is not enabled. (#8067) - Improve formatting of metric data diffs in `go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest`. (#8073) ## Deprecated - Deprecate `INVALID` in `go.opentelemetry.io/otel/attribute`. Use `EMPTY` instead. (#8038) ## Fixed - Return spec-compliant `TraceIdRatioBased` description. This is a breaking behavioral change, but it is necessary to make the implementation [spec-compliant](https://opentelemetry.io/docs/specs/otel/trace/sdk/#traceidratiobased). (#8027) - Fix a race condition in `go.opentelemetry.io/otel/sdk/metric` where the lastvalue aggregation could collect the value 0 even when no zero-value measurements were recorded. (#8056) - Limit HTTP response body to 4 MiB in `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp` to mitigate excessive memory usage caused by a misconfigured or malicious server. Responses exceeding the limit are treated as non-retryable errors. (#8108) - Limit HTTP response body to 4 MiB in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp` to mitigate excessive memory usage caused by a misconfigured or malicious server. Responses exceeding the limit are treated as non-retryable errors. (#8108) - Limit HTTP response body to 4 MiB in `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp` to mitigate excessive memory usage caused by a misconfigured or malicious server. Responses exceeding the limit are treated as non-retryable errors. (#8108) - `WithHostID` detector in `go.opentelemetry.io/otel/sdk/resource` to use full path for `kenv` command on BSD. (#8113) - Fix missing `request.GetBody` in `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp` to correctly handle HTTP2 GOAWAY frame. (#8096) --------- Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

Add W3C tracecontext IsRandom and WithRandom methods.

37c2f0d

Co-authored-by: Joshua MacDonald <jmacd@users.noreply.github.com>

yuanyuanzhao3 requested review from MrAlias, XSAM, dashpole, dmathieu, flc1125 and pellared as code owners March 6, 2026 18:45

yuanyuanzhao3 force-pushed the support-w3c-sampled-random-flags branch from 2dbdc5b to a6b577b Compare March 6, 2026 18:53

Adds change log entry for IsRandom and WithRandom method.

78be0a5

yuanyuanzhao3 force-pushed the support-w3c-sampled-random-flags branch from a6b577b to 78be0a5 Compare March 6, 2026 20:10

yuanyuanzhao3 added 2 commits March 6, 2026 15:41

Merge branch 'main' into support-w3c-sampled-random-flags

b397305

Update CHANGELOG for new features and changes

fb48fde

Added new features for W3C tracecontext random flag support in TraceFlags and SpanContext.

yuanyuanzhao3 mentioned this pull request Mar 9, 2026

Support TraceIdRatioBased Sampler #7928

Open

dashpole approved these changes Mar 11, 2026

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Merge branch 'main' into support-w3c-sampled-random-flags

d6f79b8

pellared reviewed Mar 12, 2026

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pellared changed the title ~~Add W3C tracecontext IsRandom and WithRandom methods.~~ trace: add Random Trace ID Flag Mar 12, 2026

Update CHANGELOG.md

bdb6438

Co-authored-by: Robert Pająk <pellared@hotmail.com>

pellared approved these changes Mar 12, 2026

View reviewed changes

Merge branch 'main' into support-w3c-sampled-random-flags

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dmathieu approved these changes Mar 13, 2026

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Merge branch 'main' into support-w3c-sampled-random-flags

30dc8a0

dmathieu merged commit 2ffde5a into open-telemetry:main Mar 13, 2026
31 checks passed

yuanyuanzhao3 mentioned this pull request Mar 20, 2026

[samplers/probability] Implements a traceIdRatio sampler open-telemetry/opentelemetry-go-contrib#8714

Closed

pellared added this to the v1.43.0 milestone Apr 1, 2026

yuanyuanzhao3 mentioned this pull request Apr 1, 2026

sdk/trace/x: Add experimental ProbabilitySampler #8123

Open

dmathieu mentioned this pull request Apr 2, 2026

Release v1.43.0 / v0.65.0 / v0.19.0 #8128

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trace: add Random Trace ID Flag#8012

trace: add Random Trace ID Flag#8012
dmathieu merged 8 commits intoopen-telemetry:mainfrom
yuanyuanzhao3:support-w3c-sampled-random-flags

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