[dougqh]

What Does This Do

Keeps the global tags (DD_TAGS) apart from the span defaults (DD_TRACE_SPAN_TAGS) in the tracer's config snapshot. Remote config tracing_tags behaves as before.

• Dynamic config: tracingTags now holds only the global tags, seeded from Config.getGlobalTags(). The test-runner path, rebuildTraceConfig, already did this.

• Span defaults: DD_TRACE_SPAN_TAGS (new Config.getSpanTags()), or the tags given to the builder's defaultSpanTags.

• ConfigSnapshot: keeps two frozen maps alongside mergedTracerTags:

  • globalTags: the global tags as given, or their RC override. The override keeps the configured env and version;
  • spanDefaultTags: the span defaults plus the tracer-defined tags (env, _dd.dsm.enabled, …). While an RC tracing_tags override is active, only the tracer-defined tags.

  mergedTracerTags is built from both, with span defaults winning as before. Read-through and span semantics are unchanged.

Motivation

#12813 (OTLP): to put DD_TAGS on the OTLP Resource without repeating them on every span, the exporter needs the global tags as their own set. Today it has to recover them by comparing values against the static Config. With this change, core can build the Resource from globalTags and write spanDefaultTags on spans, taking both from the trace's snapshot (TraceCollector.getTraceConfig()). The Resource then also follows RC tag changes, and keeps env and version through them. The OTLP side is a follow-up and isn't included here.

Behavior changes (release notes)

• RC tracing_tags: unchanged. While an override is active, it still replaces DD_TRACE_SPAN_TAGS along with DD_TAGS, as Add test for remote config tracing tags overriding DD_TAGS (OTLP trace/resource-level split) #12936's test pins. Languages differ here (see Add test for remote config tracing tags overriding DD_TAGS (OTLP trace/resource-level split) #12936), so whether span defaults should survive an override is left for a separate PR.
• Builder / DDTracer defaultSpanTags: explicit defaults are now the span-defaults level.
  • DD_TAGS now apply alongside them. Before, explicit defaults replaced the config tags at startup.
  • The tracer-defined tags (env, dsm/djm) are now added at startup too. Before, they were only added after an RC tag change.

Additional Notes

• Stacked on Add test for remote config tracing tags overriding DD_TAGS (OTLP trace/resource-level split) #12936. Review the commits on top of it.
• Cold path only: the maps are rebuilt only when a config snapshot's tracing tags change. Per-span work is unchanged.
• env and version in globalTags: Config.getGlobalTags() includes them when DD_ENV / DD_VERSION are set, and an RC override keeps them, so a Resource built from globalTags doesn't lose them while an override is active.
• No production reader of globalTags / spanDefaultTags yet. The consumer is the Stop repeating global tags as OTLP span attributes #12813 rebuild.
• Tests:
  • remoteConfigTracingTagsOverrideGlobalTags has a DD_TRACE_SPAN_TAGS row, expecting the override to replace span tags too;
  • new configSnapshotSeparatesGlobalTagsFromSpanDefaults, covering the override and its removal;
  • both use injectSysConfig, so each table row can set its own config.

🤖 Generated with Claude Code

[datadog-prod-us1-4]

🎯 Code Coverage (details)
• Patch Coverage: 50.00%
• Overall Coverage: 59.47% (-0.39%)

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🔗 Commit SHA: 1e46ce6 | Docs | Give us feedback!}

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	14.73 s	14.69 s	[-0.5%; +0.9%] (no difference)
startup:insecure-bank:tracing:Agent	13.51 s	13.67 s	[-1.8%; -0.5%] (maybe better)
startup:petclinic:appsec:Agent	17.15 s	17.08 s	[-0.5%; +1.4%] (no difference)
startup:petclinic:iast:Agent	17.01 s	17.11 s	[-1.3%; +0.2%] (no difference)
startup:petclinic:profiling:Agent	16.66 s	16.98 s	[-3.0%; -0.8%] (maybe better)
startup:petclinic:sca:Agent	17.09 s	16.92 s	[+0.2%; +1.8%] (maybe worse)
startup:petclinic:tracing:Agent	16.27 s	16.10 s	[-0.0%; +2.2%] (no difference)

Commit: 1e46ce6f · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-19T23:57:35.775754Z	3d144d9	Draft marked ready

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[datadog-prod-us1-4]

More details

Remote-config tracing-tag replacements preserve local span defaults, including their precedence over global tags. The completed static review identified no reportable regression.

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[mcculls]

Nice, thanks for the cleanup

I noted a small discrepancy for an edge-case where the RC tracing_tags override is exactly the same as DD_TAGS but that's not a blocker to merging this improvement.

[datadog-prod-us1-4]

An RC tracing_tags override equal to the configured global tags fails to replace span defaults. This includes an empty override intended to clear DD_TRACE_SPAN_TAGS when DD_TAGS is unset.

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