feat: add _dd.p.ksr propagated tag for Knuth sampling rate#180
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feat: add _dd.p.ksr propagated tag for Knuth sampling rate#180
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Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Expand assert! macro call to multi-line format required by rustfmt. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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This was referenced Mar 11, 2026
Co-Authored-By: Claude Opus 4.6 <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:
datadog-opentelemetry/src/core/constants.rs— AddedSAMPLING_KNUTH_RATE_TAG_KEYconstantdatadog-opentelemetry/src/sampling/datadog_sampler.rs— Addedformat_sampling_rate()helper and set ksr in agent/rule sampling pathsRelated PRs across tracers:
_dd.p.ksrformatting to use 6 significant digits without trailing zeros dd-trace-cpp#288🤖 Generated with Claude Code