fix(eap): Substitute nil trace ID by jjbayer · Pull Request #6079 · getsentry/relay

jjbayer · 2026-06-11T08:56:54Z

Nil trace IDs (UUIDs with all bytes zero) have the negative product property that they connect unrelated items into a single trace, and, if there are many of them, have negative partitioning effects (hot partitions).

Let's disallow nil trace IDs everywhere. Instead of treating them as invalid (like we would an invalid UUID), replace them with a random trace ID to avoid any product regression.

Relates to getsentry/sentry-python#6558

jjbayer · 2026-06-11T13:22:31Z

+        TraceId::try_from(*event.id.get_or_insert_with(Default::default))
+            .unwrap_or_else(|_| TraceId::random())


This was another place where nil-trace IDs could originate.

jjbayer · 2026-06-11T13:23:35Z

+impl TryFrom<EventId> for TraceId {
+    type Error = InvalidTraceId;
+    fn try_from(event_id: EventId) -> Result<Self, Self::Error> {
+        Self::try_from(event_id.0)
    }
 }

-impl From<Uuid> for TraceId {
-    fn from(uuid: Uuid) -> Self {
-        TraceId(uuid)
+impl From<TraceId> for Uuid {
+    fn from(trace_id: TraceId) -> Self {
+        trace_id.0
    }
 }

-impl From<EventId> for TraceId {
-    fn from(event_id: EventId) -> Self {
-        Self::from(event_id.0)
+impl fmt::Display for TraceId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.0.as_simple())
    }
 }

-impl From<TraceId> for Uuid {
-    fn from(trace_id: TraceId) -> Self {
-        trace_id.0
+impl fmt::Debug for TraceId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "TraceId(\"{}\")", self.0.as_simple())


I moved the constructors up so they are all in one place. Messes with the diff but makes for better readability over all IMO.

jjbayer · 2026-06-11T13:24:03Z

@@ -1,5 +1,5 @@
 {
-  "trace_id": "00000000-0000-0000-0000-000000000000",
+  "trace_id": "00000000-0000-0000-0000-000000000001",


Tests with nil IDs would now fail.

jjbayer · 2026-06-11T13:24:46Z

        Some((kv.key, Annotated::new(attr_value)))
    }));

+    let trace_id = TraceId::try_from_or_random(otel_link.trace_id.as_slice());


try_from_or_random is used in other Otel converters, so I thought I might as well use it here.

Dav1dde · 2026-06-11T13:52:08Z

+    /// Not a valid UUID.
+    Uuid,


nit: Maybe no need to leak that there is an underlying uuid id as there are defined rules for trace ids which don't necessarily match a uuid. Could just call it Invalid.

Dav1dde · 2026-06-11T13:52:49Z

-        Ok(Self(uuid))
+        Uuid::from_slice(value)
+            .map_err(|_| InvalidTraceId::Uuid)
+            .map(TraceId)


Shouldn't this delegate to TryFrom<Uuid> other wise the nil check is missing?

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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cursor · 2026-06-11T14:17:54Z

+        if uuid.is_nil() {
+            return Err(InvalidTraceId::Nil);
+        }
+        Ok(TraceId(uuid))


Serde nil IDs not substituted

Medium Severity

TryFrom/FromStr now reject all-zero trace IDs, and impl_str_serde deserializes through FromStr. Nil IDs in types like DynamicSamplingContext fail parsing instead of being replaced with a random ID, unlike the FromValue path that substitutes nil and records nil_trace_id.

Additional Locations (1)

relay-event-schema/src/protocol/contexts/trace.rs#L66-L67

^{Reviewed by Cursor Bugbot for commit 4b98c24. Configure here.}

In a follow-up PR I will make parsing more restrictive and always reject on nil IDs. For now, an error in the DSC will hit the error boundary and default to None.

sentry · 2026-06-11T14:35:39Z

        Some((kv.key, Annotated::new(attr_value)))
    }));

+    let trace_id = TraceId::try_from_or_random(otel_link.trace_id.as_slice());
    let span_link = SpanV2Link {
-        trace_id: Annotated::new(hex::encode(otel_link.trace_id).parse()?),
+        trace_id,
        span_id: SpanId::try_from(otel_link.span_id.as_slice())?.into(),
        sampled: (otel_link.flags & W3C_TRACE_CONTEXT_SAMPLED != 0).into(),
        attributes: Annotated::new(attributes),


Bug: The try_from_or_random function incorrectly generates a "trace_id.invalid" remark for nil OTel trace IDs instead of "nil_trace_id", because it only checks if the slice is empty.
_{Severity: LOW}

Suggested Fix

Modify try_from_or_random to handle the InvalidTraceId::Nil error case specifically. This can be done by changing the error handling to pattern match on the error type, similar to how FromValue::from_value is implemented, to distinguish between a nil ID and a generally invalid one. This will allow it to generate the correct "nil_trace_id" remark.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not valid. Location: relay-spans/src/otel_to_sentry_v2.rs#L194-L202 Potential issue: When processing an OTel span link with a nil trace ID (16 zero bytes), the `TraceId::try_from_or_random` function is called. The underlying `TryFrom<Uuid> for TraceId` implementation correctly identifies the nil ID and returns an `InvalidTraceId::Nil` error. However, the `try_from_or_random` function discards this specific error information. It then checks if the input slice `is_empty()`, which is false for a 16-byte nil ID. Consequently, it incorrectly adds a remark of `"trace_id.invalid"` instead of the expected `"nil_trace_id"`. This prevents a metric counter, which specifically checks for the `"nil_trace_id"` remark, from being incremented, creating an observability gap.

Also affects:

relay-event-schema/src/protocol/contexts/trace.rs:66~139

fix(eap): Substitute nil trace ID

8b89e01

jjbayer mentioned this pull request Jun 11, 2026

fix(trace-metrics): Replace nil trace IDs with a random one #6077

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jjbayer added 4 commits June 11, 2026 13:53

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jjbayer marked this pull request as ready for review June 11, 2026 12:27

jjbayer requested a review from a team as a code owner June 11, 2026 12:27

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Comment thread relay-spans/src/otel_to_sentry_v2.rs

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Comment thread relay-event-schema/src/protocol/contexts/trace.rs

jjbayer marked this pull request as draft June 11, 2026 12:47

fix

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jjbayer commented Jun 11, 2026

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jjbayer marked this pull request as ready for review June 11, 2026 13:25

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Comment thread relay-event-schema/src/protocol/contexts/trace.rs Outdated

jjbayer added 2 commits June 11, 2026 15:38

Merge branch 'master' into fix/substitute-nil-trace-id

3f94dd5

whoops

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Comment thread relay-spans/src/otel_to_sentry_v2.rs

Dav1dde requested changes Jun 11, 2026

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Don't mention the UUID

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use new variant name

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fix(eap): Substitute nil trace ID#6079

fix(eap): Substitute nil trace ID#6079
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fix/substitute-nil-trace-id

jjbayer commented Jun 11, 2026 •

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		TraceId::try_from(*event.id.get_or_insert_with(Default::default))
		.unwrap_or_else(\|_\| TraceId::random())

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Serde nil IDs not substituted

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jjbayer commented Jun 11, 2026 •

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