Wire OTLP Trace Metrics Writers into Metrics Aggregators

[mhlidd]

What Does This Do

This PR wires the OTLP Trace Metrics logic and writers into the existing Metrics Aggregators used for Client Side Stats.

This involves:

• Adding a new OTLP export variant for ConflatingMetricsAggregator which uses the OtlpStatsMetricWriter introduced in BETA: Define OTLP Trace Metrics Histogram and Writers #11656
• Making native CSS metrics mutually exclusive w/ OTLP Trace Metrics
• Dropping sampled traces when OTLP Trace Metrics is active
• Adding the Datadog-Client-Computed-Stats header when OTLP Trace Metrics are active to prevent dual writing in the Agent
• Adding package-private getters in ConflatingMetricsAggregator for testing purposes

Motivation

Additional Notes

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Jira ticket: [PROJ-IDENT]

[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	13.96 s	14.03 s	[-1.2%; +0.1%] (no difference)
startup:insecure-bank:tracing:Agent	13.00 s	12.97 s	[-0.4%; +0.9%] (no difference)
startup:petclinic:appsec:Agent	16.78 s	16.76 s	[-1.1%; +1.2%] (no difference)
startup:petclinic:iast:Agent	16.86 s	16.88 s	[-0.9%; +0.7%] (no difference)
startup:petclinic:profiling:Agent	16.58 s	16.72 s	[-1.8%; +0.2%] (no difference)
startup:petclinic:sca:Agent	16.85 s	16.70 s	[+0.0%; +1.8%] (maybe worse)
startup:petclinic:tracing:Agent	15.51 s	16.11 s	[-7.8%; +0.4%] (no difference)

Commit: 0e5a05fb · 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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[chatgpt-codex-connector]

Move the new stats-header coverage to JUnit 5

The root AGENTS.md says, "Always use JUnit 5" and "Do not write new Groovy / Spock tests"; this adds a new Spock feature method to DDAgentApiTest.groovy. Please move this coverage to a JUnit 5 test (or migrate the existing file) instead of adding new Groovy/Spock test code.

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[mcculls]

Instead of continually adding boolean flags which could become fragile (i.e. remembering the order of the flags) we could consider providing a Map<String, String> of additional attributes.

Then you could create a static initializer block under TRACE_RESOURCE_MESSAGE

For example, something like:

  Map<String, String> extraAttributes = new HashMap<>();
  if (Config.get().isTracesSpanMetricsEnabled()) {
    extraAttributes.put(STATS_COMPUTED_KEY, "true");
  }
  TRACE_RESOURCE_MESSAGE =
      buildResourceMessage(Config.get(), false, extraAttributes);

The buildResourceMessage method would then iterate over the extraAttributes entries, building them into the final resource payload.

[mhlidd]

Good idea! I replaced the static block w/ a helper function that get's called instead. Let me know if you feel strongly about using the static initializer block instead.

[mcculls]

Some comments/improvements to be addressed - after that this can be merged into the parent PR for a final review of the overall picture.

[datadog-datadog-prod-us1]

More details

The XOR logic in MetricsAggregatorFactory correctly gates OTLP vs native stats, the DroppingPolicy lambda captures the OTLP flag at construction time to always-drop p0 traces when active, and DDAgentApi's Datadog-Client-Computed-Stats header OR-combines both pipelines — matching the existing Config.get() call pattern already present for isApmTracingEnabled(). No behavioral regressions found across 10+ adversarial scenarios covering gRPC fallback extraction, service-name per-point logic, resource attribute selection, and factory selection XOR. Tests could not be executed due to a Java 25 toolchain requirement (only Java 8–21 available in the sandbox), so the analysis is static.

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