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fix: keep custom exemplar labels caller-controlled #2194

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Merged
jaydeluca merged 1 commit into from
Jun 5, 2026
+21 −15
Merged

fix: keep custom exemplar labels caller-controlled #2194

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24 changes: 15 additions & 9 deletions ...heus-metrics-core/src/main/java/io/prometheus/metrics/core/exemplars/ExemplarSampler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -339,7 +339,7 @@ private long durationUntilNextExemplarExpires(long now) {

private long updateCustomExemplar(int index, double value, Labels labels, long now) {
if (!labels.contains(Exemplar.TRACE_ID) && !labels.contains(Exemplar.SPAN_ID)) {
labels = mergeLabels(labels, doSampleExemplar());
labels = mergeLabels(labels, sampleTraceContextLabels());
}
customExemplars[index] =
Exemplar.builder().value(value).labels(labels).timestampMillis(now).build();
Expand All @@ -358,6 +358,19 @@ private long updateExemplar(int index, double value, long now) {
}

private Labels doSampleExemplar() {
Labels labels = sampleTraceContextLabels();
if (labels.isEmpty()) {
return labels;
}
// Per-metric supplier first (more specific), then the global supplier. On a name
// collision the earlier (more specific) value is kept; the reserved trace_id/span_id
// labels always win over both.
labels = mergeAdditionalLabels(labels, additionalLabelsSupplier);
labels = mergeAdditionalLabels(labels, ExemplarLabelsSupplier.getExemplarLabelsSupplier());
return labels;
}

private Labels sampleTraceContextLabels() {
// Using the qualified name so that Micrometer can exclude the dependency on
// prometheus-metrics-tracer-initializer
// as they provide their own implementation of SpanContextSupplier.
Expand All @@ -374,14 +387,7 @@ private Labels doSampleExemplar() {
String traceId = spanContext.getCurrentTraceId();
if (spanId != null && traceId != null) {
spanContext.markCurrentSpanAsExemplar();
Labels labels = Labels.of(Exemplar.TRACE_ID, traceId, Exemplar.SPAN_ID, spanId);
// Per-metric supplier first (more specific), then the global supplier. On a name
// collision the earlier (more specific) value is kept; the reserved trace_id/span_id
// labels always win over both.
labels = mergeAdditionalLabels(labels, additionalLabelsSupplier);
labels =
mergeAdditionalLabels(labels, ExemplarLabelsSupplier.getExemplarLabelsSupplier());
return labels;
return Labels.of(Exemplar.TRACE_ID, traceId, Exemplar.SPAN_ID, spanId);
}
}
}
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12 changes: 6 additions & 6 deletions prometheus-metrics-core/src/test/java/io/prometheus/metrics/core/metrics/CounterTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -502,22 +502,22 @@ void globalSupplierWithoutSpanContextProducesNoExemplar() {
}

@Test
void globalSupplierMergedIntoCustomExemplar() throws Exception {
void globalSupplierDoesNotApplyToCustomExemplar() throws Exception {
SpanContextSupplier.setSpanContext(sampledSpanContext("trace-abc", "span-def"));
ExemplarLabelsSupplier.setExemplarLabelsSupplier(() -> Labels.of("management_id", "mgmt-42"));

Counter counter = Counter.builder().name("requests_total").build();
counter.incWithExemplar(Labels.of("k", "v"));

assertThat(openMetrics(counter))
.contains("management_id=\"mgmt-42\"")
.contains("k=\"v\"")
.contains("trace_id=\"trace-abc\"")
.contains("span_id=\"span-def\"");
.contains("span_id=\"span-def\"")
.doesNotContain("management_id=\"mgmt-42\"");
}

@Test
void callerLabelsWinOverGlobalSupplierInCustomExemplar() throws Exception {
void callerControlsCustomExemplarLabels() throws Exception {
SpanContextSupplier.setSpanContext(sampledSpanContext("trace-abc", "span-def"));
ExemplarLabelsSupplier.setExemplarLabelsSupplier(
() -> Labels.of("k", "global", "management_id", "mgmt-42"));
Expand All @@ -527,10 +527,10 @@ void callerLabelsWinOverGlobalSupplierInCustomExemplar() throws Exception {

assertThat(openMetrics(counter))
.contains("k=\"caller\"")
.contains("management_id=\"mgmt-42\"")
.contains("trace_id=\"trace-abc\"")
.contains("span_id=\"span-def\"")
.doesNotContain("k=\"global\"");
.doesNotContain("k=\"global\"")
.doesNotContain("management_id=\"mgmt-42\"");
}

@Test
Expand Down