RUM-15138: Preserve custom DeterministicTraceSampler subclasses from rebasing#3455
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hamorillo merged 1 commit intoMay 19, 2026
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…rebasing Tighten the SessionRebasedSampler wrap condition in DatadogInterceptor.Builder and ApmNetworkInstrumentationConfiguration.createInstrumentation from `is DeterministicTraceSampler` to an exact-class check, so subclasses passed via setTraceSampler are preserved as-is and bypass cross-product rebasing. This matches the documented setTraceSampler contract that custom samplers should not be rebased. Updated KDoc on setTraceSampler in TracingInterceptor and ApmNetworkInstrumentationConfiguration to clarify that subclasses of DeterministicTraceSampler are also treated as custom samplers and that only an exact DeterministicTraceSampler instance (equivalent to setTraceSampleRate) participates in rebasing. Added test coverage in DatadogInterceptorBuilderTest and ApmInstrumentationConfigurationTest asserting subclass instances are not wrapped.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## develop #3455 +/- ##
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- Coverage 72.22% 72.17% -0.05%
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Files 964 964
Lines 35497 35500 +3
Branches 5896 5897 +1
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- Hits 25635 25620 -15
- Misses 8258 8263 +5
- Partials 1604 1617 +13
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hamorillo
marked this pull request as ready for review
May 19, 2026 09:01
0xnm
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May 19, 2026
kikoveiga
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May 19, 2026
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What does this PR do?
Replaces the
is DeterministicTraceSamplertype check at two call sites (DatadogInterceptor.Builder.build()andApmNetworkInstrumentationConfiguration.createInstrumentation) with an exact-class match, so subclasses ofDeterministicTraceSamplerpassed viasetTraceSampler()are preserved as custom samplers and bypass cross-product rebasing. KDoc onsetTraceSamplerinTracingInterceptorandApmNetworkInstrumentationConfigurationupdated to clarify this behavior.Motivation
Codex flagged a P2 in PR #3454: when a customer passes a
DeterministicTraceSamplersubclass viasetTraceSampler(), the previousis DeterministicTraceSamplercheck still wrapped it inSessionRebasedSampler. InsideSessionRebasedSampler.sample(), when the combined rate differs from the raw rate, a freshDeterministicTraceSampler(effectiveRate)is constructed and used — silently bypassing the customer's subclass logic. This contradicts the documentedsetTraceSamplercontract that custom samplers do not participate in cross-product rebasing.With the exact-class match, only an exact
DeterministicTraceSamplerinstance (which is whatsetTraceSampleRateproduces internally) is wrapped. Subclasses and any other customSampler<DatadogSpan>are preserved as-is.Review checklist (to be filled by reviewers)