Add _dd.p.ksr propagated tag for Knuth sampling rate#7741
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Add _dd.p.ksr propagated tag for Knuth sampling rate#7741
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Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Overall package sizeSelf size: 4.95 MB Dependency sizes| name | version | self size | total size | |------|---------|-----------|------------| | import-in-the-middle | 3.0.0 | 81.15 kB | 815.98 kB | | dc-polyfill | 0.1.10 | 26.73 kB | 26.73 kB |🤖 This report was automatically generated by heaviest-objects-in-the-universe |
BenchmarksBenchmark execution time: 2026-03-11 02:53:56 Comparing candidate commit 8a10db8 in PR branch Found 0 performance improvements and 0 performance regressions! Performance is the same for 230 metrics, 30 unstable metrics. |
This was referenced Mar 11, 2026
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #7741 +/- ##
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Coverage 80.40% 80.40%
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Files 741 741
Lines 32084 32090 +6
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+ Hits 25796 25802 +6
Misses 6288 6288
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Only set the SAMPLING_KNUTH_RATE (_dd.p.ksr) tag when actual agent rates have been received (SAMPLING_MECHANISM_AGENT), not when using the built-in default sampler (SAMPLING_MECHANISM_DEFAULT). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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What does this PR do?
Adds
_dd.p.ksr(Knuth Sampling Rate) as a propagated tag set when agent-based or rule-based sampling decisions are made. The tag is stored in spanmeta(string type) with up to 6 significant digits and no trailing zeros.Motivation
To enable consistent sampling across tracers and backend retention filters, the backend needs to know the sampling rate applied by the tracer. Without transmitting the tracer's rate via
_dd.p.ksr, backend resampling cannot correctly compute effective rates in multi-stage sampling scenarios.See RFC: "Transmit Knuth sampling rate to backend"
Additional Notes
Key files changed:
packages/dd-trace/src/constants.js— AddedSAMPLING_KNUTH_RATEconstantpackages/dd-trace/src/priority_sampler.js— AddedformatKnuthRate()and set ksr in agent/rule sampling pathspackages/dd-trace/test/priority_sampler.spec.js— 7 test casesRelated PRs across tracers:
_dd.p.ksrformatting to use 6 significant digits without trailing zeros dd-trace-cpp#288🤖 Generated with Claude Code