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Use float for sample rand #4677

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Use float for sample rand #4677

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@sentrivana sentrivana commented Aug 6, 2025 •
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Closes #4270

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codecov bot commented Aug 6, 2025 •
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Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.05%. Comparing base (46eb82c) to head (e46a07e).
✅ All tests successful. No failed tests found.

Files with missing lines Patch % Lines
sentry_sdk/utils.py 50.00% 1 Missing and 1 partial ⚠️
Additional details and impacted files 
@@            Coverage Diff             @@
##           master    #4677      +/-   ##
==========================================
- Coverage   85.09%   85.05%   -0.04%     
==========================================
  Files         156      156              
  Lines       15869    15867       -2     
  Branches     2689     2689              
==========================================
- Hits        13503    13495       -8     
- Misses       1585     1587       +2     
- Partials      781      785       +4
Files with missing lines Coverage Δ
sentry_sdk/integrations/asgi.py 90.71% <100.00%> (+0.06%) ⬆️
sentry_sdk/tracing.py 85.77% <100.00%> (-0.45%) ⬇️
sentry_sdk/tracing_utils.py 87.40% <100.00%> (-0.87%) ⬇️
sentry_sdk/utils.py 88.32% <50.00%> (-0.20%) ⬇️

... and 1 file with indirect coverage changes

@sentrivana sentrivana changed the title Remove Decimal Use float for sample rand Aug 6, 2025
@sentrivana sentrivana marked this pull request as ready for review August 7, 2025 11:14
@sentrivana sentrivana requested a review from a team as a code owner August 7, 2025 11:14
@sentrivana sentrivana changed the base branch from ivana/random-perf-improvements to master August 7, 2025 14:30
@sentrivana sentrivana marked this pull request as draft August 12, 2025 11:31
cursor[bot]
cursor bot reviewed Aug 12, 2025
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sentry_sdk/tracing_utils.py
)
sample_rand_scaled = rng.randrange(int(lower * 1000000), int(upper * 1000000))

return sample_rand_scaled / 1000000
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Bug: Sampling Context Propagation Fails for Tiny Rates

The _generate_sample_rand function's integer scaling for randrange arguments (int(value * 1e6)) can cause the start and stop values to become equal for very narrow intervals (less than 1e-6). This leads randrange to raise a ValueError ("empty range"). This error is caught in PropagationContext._fill_sample_rand, which then silently skips setting the sample_rand. As a result, dynamic sampling context propagation fails for traces with small sample_rates (e.g., when parent_sampled=True with a tiny sample_rate), leading to inconsistent sampling decisions across services.

Fix in Cursor Fix in Web

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Move away from Decimal
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