[vpellan]

Description

Add support for OTel sampling in distributed tracing, by reading and emitting ot.th and ot.rv tags. These tags will be forwarded to services using OTel SDKs, that should forward them to the backend.

Distributed tracing will work between DD-instrumented services and OTel-instrumented services, downstream OTel services will be able to forward the th field it to the collector and backend, which will calculate metrics correctly

Locally passes DataDog/system-tests#7518

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[datadog-datadog-prod-us1]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 68.26% (-0.01%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 927f2b8 | Docs | View more details | Give us feedback!}

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-09T15:05:34.839614Z	f7329a3	PR opened
🔒 Security Review	✅ Completed 2026-09-09T15:01:51.128033Z	f7329a3	PR opened

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: f7329a3d7e

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[github-actions]

Snapshots difference summary

The following differences have been observed in committed snapshots. It is meant to help the reviewer.
The diff is simplistic, so please check some files anyway while we improve it.

If you need to update snapshots, please refer to CONTRIBUTING.md

2 occurrences of :

- "_dd.span_links": "[{\"trace_id\":\"0000000000000000c151df7d6ee5e2d6\",\"span_id\":\"c151df7d6ee5e2d6\",\"trace_state\":\"dd=t.dm:-0\",\"attributes\":{\"_dd.p.dm\":\"-0\"}}]"
+ "_dd.span_links": "[{\"trace_id\":\"0000000000000000c151df7d6ee5e2d6\",\"span_id\":\"c151df7d6ee5e2d6\",\"trace_state\":\"dd=t.dm:-0,ot=rv:ea5f0f7db45435;th:0\",\"attributes\":{\"_dd.p.dm\":\"-0\"}}]"

[pr-commenter]

Benchmarks [ tracer ]

Benchmark execution time: 2026-09-14 19:15:08

Comparing candidate commit 38c7c80 in PR branch vpellan/otel-threshold-random-value with baseline commit c40e013 in branch master.

Found 0 performance improvements and 14 performance regressions! Performance is the same for 179 metrics, 1 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:ContextPropagationBench/benchExtractHeaders128Bit

• 🟥 execution_time [+53.067ns; +93.600ns] or [+6.199%; +10.935%]

scenario:ContextPropagationBench/benchExtractHeaders128Bit-opcache

• 🟥 execution_time [+37.390ns; +103.943ns] or [+2.159%; +6.001%]

scenario:ContextPropagationBench/benchExtractHeaders64Bit-opcache

• 🟥 execution_time [+41.820ns; +124.180ns] or [+3.468%; +10.297%]

scenario:ContextPropagationBench/benchExtractTraceContext128Bit

• 🟥 execution_time [+43.401ns; +114.599ns] or [+2.338%; +6.174%]

scenario:ContextPropagationBench/benchExtractTraceContext64Bit

• 🟥 execution_time [+60.018ns; +77.982ns] or [+7.094%; +9.218%]

scenario:ContextPropagationBench/benchExtractTraceContext64Bit-opcache

• 🟥 execution_time [+61.646ns; +80.354ns] or [+7.287%; +9.498%]

scenario:SamplingRuleMatchingBench/benchRegexMatching1

• 🟥 execution_time [+55.872ns; +118.728ns] or [+3.626%; +7.706%]

scenario:SamplingRuleMatchingBench/benchRegexMatching2

• 🟥 execution_time [+43.056ns; +86.744ns] or [+2.771%; +5.582%]

scenario:SpanBench/benchOpenTelemetryAPI

• 🟥 execution_time [+18.321µs; +31.697µs] or [+2.178%; +3.768%]
• 🟥 mem_peak [+4.343MB; +4.343MB] or [+8.309%; +8.309%]

scenario:SpanBench/benchOpenTelemetryAPI-opcache

• 🟥 mem_peak [+4.341MB; +4.341MB] or [+8.821%; +8.821%]

scenario:SpanBench/benchOpenTelemetryInteroperability

• 🟥 execution_time [+11.371µs; +15.973µs] or [+5.211%; +7.320%]
• 🟥 mem_peak [+1.076MB; +1.076MB] or [+3.649%; +3.649%]

scenario:SpanBench/benchOpenTelemetryInteroperability-opcache

• 🟥 mem_peak [+1.074MB; +1.074MB] or [+4.072%; +4.072%]

[bwoebi]

Looks good to me now, thanks!