Add _dd.svc_src to distinguish source

[TonyCTHsu]

What does this PR do?

Adds a new _dd.svc_src tag on spans whose service name has been overridden from the global default service. The value identifies the source of the override: the integration component name (e.g. redis, pg, sidekiq) for Datadog-instrumented spans, or m for manually-instrumented spans.

The tag is set in each contrib alongside the existing span.service = override, and a fallback m value is applied in the span_before_finish hook for any service-overridden span that does not already carry the tag. The tag is removed when the span's service ends up matching the global default service.

This complements the existing _dd.base_service tag, which records the global default service when a span overrides it.

Motivation:

Backends and downstream consumers need to distinguish manually-set service overrides from those applied by Datadog integrations, so they can attribute service-naming behavior correctly.

Change log entry

None.

Additional Notes:

This PR is stacked on top of tonycthsu/before_finish_event — please review and merge that branch first. The fallback m tagging relies on the span_before_finish event introduced there.

How to test the change?

• Trigger a span via an instrumented integration (e.g. Redis) with a custom service_name configured — span should carry _dd.svc_src = redis.
• Manually create a span with Tracing.trace('op', service: 'custom') { ... } — span should carry _dd.svc_src = m.
• Create a span whose service matches the global default service — span should not carry _dd.svc_src.

[dd-octo-sts]

Thank you for updating Change log entry section 👏

^{Visited at: 2026-05-19 12:52:01 UTC}

[dd-octo-sts]

Typing analysis

This PR does not change typing compared to the base branch.

[datadog-official]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 90.37%
• Overall Coverage: 97.07% (-0.02%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 539a132 | Docs | Datadog PR Page | Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-05-28 08:54:45

Comparing candidate commit 539a132 in PR branch tonycthsu/source-attri with baseline commit b1a5c02 in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 45 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 ----------------------------------'

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