Place _dd.apm.enabled:0 in every span

[cataphract]

Description

Although the RFC says otherwise (only to place it on the first span in the chunk), his is the safest way to ensure _dd.apm.enabled is encountered during processing and was the consensus decision following an incident.

Motivation

Additional Notes

Jira ticket: [PROJ-IDENT]

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-07-23 12:03:10

Comparing candidate commit e9174ad in PR branch glopes/_dd.apm.enabled-everywhere with baseline commit 24f765c in branch main.

Found 0 performance improvements and 3 performance regressions! Performance is the same for 5 metrics, 0 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:BM_TraceID_HexPadded/WithPadding

• 🟥 execution_time [+10.084ns; +20.197ns] or [+7.455%; +14.932%]

scenario:BM_TraceID_ParseHex/128bit

• 🟥 execution_time [+13.996ns; +14.035ns] or [+11.448%; +11.479%]

scenario:BM_TraceID_ParseHex/64bit

• 🟥 execution_time [+4.859ns; +4.893ns] or [+7.016%; +7.065%]

[datadog-prod-us1-4]

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⚠️ Warnings

🚦 2 Pipeline jobs failed

DataDog/apm-reliability/dd-trace-cpp | check-big-regressions     

Development | build-linux-cmake (llvm, x64)     

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