Fix _dd.p.ksr formatting to use 6 significant digits without trailing zeros#288
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Fix _dd.p.ksr formatting to use 6 significant digits without trailing zeros#288
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Replace std::to_string() (which uses sprintf "%f" producing 6 trailing
decimal places) with snprintf "%.6g" which produces up to 6 significant
digits with no trailing zeros. This matches the behavior of Python's
f"{rate:.6g}" and Go's strconv.FormatFloat(rate, 'g', 6, 64).
Examples: 1.0 -> "1", 0.5 -> "0.5", 0.0 -> "0"
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
BenchmarksBenchmark execution time: 2026-03-11 02:52:05 Comparing candidate commit ef4d91b in PR branch Found 0 performance improvements and 0 performance regressions! Performance is the same for 1 metrics, 0 unstable metrics. |
Reformat the emplace_back call to match clang-format's expected style (arguments on one line with alignment) to fix the verify CI job. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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 @@
## main #288 +/- ##
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+ Coverage 87.76% 87.78% +0.01%
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Files 84 84
Lines 5658 5663 +5
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+ Hits 4966 4971 +5
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The ksr trace tag should only be set when the sampling decision comes from an explicit source (agent rate, rule, or remote rule). When the DEFAULT mechanism is used — meaning no agent configuration has been received yet — the rate is a hardcoded 100% and ksr is meaningless. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Description
Fixes
_dd.p.ksrvalue formatting fromstd::to_string()(which produces trailing zeros like"1.000000") tosnprintf("%.6g")(no trailing zeros, up to 6 significant digits). This aligns C++ with all other tracer implementations.Motivation
The C++ tracer already set
_dd.p.ksrbut usedstd::to_string()for formatting, which always produces 6 decimal places (e.g.,"1.000000"instead of"1"). The RFC specifies up to 6 significant digits with no trailing zeros, matching the%.6gformat specifier used by all other tracers.See RFC: "Transmit Knuth sampling rate to backend"
Additional Notes
Key files changed:
src/datadog/trace_segment.cpp— Addedformat_rate()helper usingsnprintf("%.6g")test/test_trace_segment.cpp— Updated 3 assertionstest/test_span.cpp— Updated 6 W3C tracestate expectationsRelated PRs across tracers:
Jira ticket: APMSP-1867
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