Incorrect sampling decision propagated in some cases in span streaming #6856

Activity

1. sentrivana

   self-assigned this

   on Jul 21, 2026
2. linear-code commented on Jul 21, 2026

   

   linear-codeBot

   on Jul 21, 2026 – with Linear Code

   More actions

   PY-2618
3. sentrivana

   added

   Component: SDK CoreDealing with the core of the SDKDealing with the core of the SDK

   Bug

   Traces

   on Jul 21, 2026
4. sentry-pierre

   added

   Feature: Span streaming

   on Jul 21, 2026
5. sentry-pierre commented on Jul 21, 2026

   

   sentry-pierreBot

   on Jul 21, 2026

   More actions

   In sentry_sdk/tracing_utils.py, _make_sampling_decision handles inherited decisions differently from the old transaction model:

   • Old model (tracing.py): when traces_sampler is undefined and parent_sampled is present, it uses parent_sampled directly as the sample rate (False → 0.0, immediately dropped).
   • New span-streaming model (tracing_utils.py): when parent_sampled is present, it prefers propagation_context._sample_rate() from baggage. If that rate is positive, it recomputes sampled = sample_rand < sample_rate, which can override the incoming 0.

   This means an incoming header with sampled=0 but sample_rate=1.0 and sample_rand=0.1 gets incorrectly sampled. The existing test_continue_trace_unsampled passes because sample_rand=0.999999 is already above sample_rate=0.5, so the bug is masked.

   A maintainer can take it from here.
6. sentrivana

   added a commit that references this issue on Jul 23, 2026

   fix(sampling): `sentry-trace` should take precedence over baggage (#6863

   ...

   3e163b1
7. sentrivana

   closed this as completedin #6863on Jul 23, 2026
8. mgaligniana

   added a commit that references this issue on Aug 9, 2026

   fix(sampling): `sentry-trace` should take precedence over baggage (ge…

   ...

   991fc89