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stefanosiano merged 7 commits into from
Oct 29, 2025
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Collect PerformanceCollectionData only in sampled transactions #4834

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performance data collection is now started only when the transaction …
stefanosiano Oct 24, 2025
eaea0dd
updated changelog
stefanosiano Oct 24, 2025
f1b1540
fixed test
stefanosiano Oct 24, 2025
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Merge branch 'main' into stefanosiano/enh/collect-performance-sampled…
stefanosiano Oct 29, 2025
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updated changelog
stefanosiano Oct 29, 2025
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updated changelog
stefanosiano Oct 29, 2025
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compositePerformanceCollector is now set only when transaction is sam…
stefanosiano Oct 29, 2025
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6 changes: 6 additions & 0 deletions CHANGELOG.md
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@@ -1,5 +1,11 @@
# Changelog

## Unreleased

### Miscellaneous

- Collect PerformanceCollectionData only in sampled transactions ([#4834](https://github.com/getsentry/sentry-java/pull/4834))
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## 8.24.0

### Features
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4 changes: 2 additions & 2 deletions sentry/src/main/java/io/sentry/SentryTracer.java
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Expand Up @@ -90,8 +90,8 @@ public SentryTracer(
}

// We are currently sending the performance data only in profiles, but we are always sending
// performance measurements.
if (compositePerformanceCollector != null) {
// performance measurements (frames data in spans).
if (compositePerformanceCollector != null && Boolean.TRUE.equals(isSampled())) {
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compositePerformanceCollector.start(this);
}
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@seer-by-sentry seer-by-sentry Bot Oct 24, 2025

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Bug: compositePerformanceCollector fails to start for transactions with deferred sampling decisions that are later marked as sampled.
Severity: CRITICAL | Confidence: 0.98

🔍 Detailed Analysis

When a transaction is created with a deferred sampling decision (samplingDecision = null), the SentryTracer constructor evaluates Boolean.TRUE.equals(isSampled()). Since isSampled() returns null, this condition is false, preventing compositePerformanceCollector.start() from being called. If the transaction is later sampled via setSamplingDecision(new TracesSamplingDecision(true)), the performance collector remains unstarted, resulting in a loss of performance data for that transaction. Additionally, compositePerformanceCollector.stop() is unconditionally called during finish(), potentially on an uninitialized collector.

💡 Suggested Fix

Modify the SentryTracer constructor to start compositePerformanceCollector if isSampled() is null, or add logic within setSamplingDecision() to start the collector if it wasn't previously started and the transaction becomes sampled.

🤖 Prompt for AI Agent 
Fix this bug. In sentry/src/main/java/io/sentry/SentryTracer.java at lines 94-96: When a
transaction is created with a deferred sampling decision (`samplingDecision = null`),
the `SentryTracer` constructor evaluates `Boolean.TRUE.equals(isSampled())`. Since
`isSampled()` returns `null`, this condition is `false`, preventing
`compositePerformanceCollector.start()` from being called. If the transaction is later
sampled via `setSamplingDecision(new TracesSamplingDecision(true))`, the performance
collector remains unstarted, resulting in a loss of performance data for that
transaction. Additionally, `compositePerformanceCollector.stop()` is unconditionally
called during `finish()`, potentially on an uninitialized collector.

Did we get this right? 👍 / 👎 to inform future reviews.

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@stefanosiano stefanosiano Oct 24, 2025

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this is the only case why we didn't do it before
should we ignore it?

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@romtsn romtsn Oct 28, 2025 •
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hmm, yeah I think this is valid actually. Probably we can't simply just do that without a breaking change - but even then I think we'd have to discuss this. I'd imagine if we ever do tail-based sampling (and we probably will), setSamplingDecision will be useful for that. So maybe this PR has to be backlogged for now

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@stefanosiano stefanosiano Oct 28, 2025

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got it
on the other side, if the sample rate is like 0.01, we'd run the performance collection 10k times more than needed 😅
Let's discuss it in the next sync


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10 changes: 8 additions & 2 deletions sentry/src/test/java/io/sentry/SentryTracerTest.kt
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Expand Up @@ -1170,11 +1170,17 @@ class SentryTracerTest {
}

@Test
fun `when transaction is created, but not profiled, compositePerformanceCollector is started anyway`() {
val transaction = fixture.getSut()
fun `when transaction is created and sampled, but not profiled, compositePerformanceCollector is started anyway`() {
val transaction = fixture.getSut(samplingDecision = TracesSamplingDecision(true))
verify(fixture.compositePerformanceCollector).start(anyOrNull<ITransaction>())
}

@Test
fun `when transaction is created, but not sampled, compositePerformanceCollector is not started`() {
val transaction = fixture.getSut(samplingDecision = TracesSamplingDecision(false))
verify(fixture.compositePerformanceCollector, never()).start(anyOrNull<ITransaction>())
}

@Test
fun `when transaction is created and profiled compositePerformanceCollector is started`() {
val transaction =
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