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…attribute labels prometheus client-go rejects exemplars whose combined label runes exceed ExemplarMaxRunes (128). addExemplars previously let that error propagate and dropped every exemplar for the data point when the limit was hit, even though the trace and span ID labels alone are well within the limit. Instead, drop the filtered-attribute-derived labels and keep the trace and span IDs when the combined labels would exceed the limit, logging a warning so the truncation is visible. Fixes open-telemetry#6718
om7057
requested review from
MrAlias,
XSAM,
dashpole,
dmathieu,
flc1125,
pellared and
ps-mir
as code owners
September 26, 2026 18:37
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #9031 +/- ##
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Coverage 89.1% 89.1%
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Files 338 338
Lines 22274 22287 +13
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+ Hits 19854 19867 +13
Misses 2420 2420
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kijimad
reviewed
Sep 28, 2026
| - Retain instrument advisory attributes (`metric/x.WithDefaultAttributes`) when a matching View does not specify an attribute filter in `go.opentelemetry.io/otel/sdk/metric`. (#8859) | ||
| - Ignore HTTP URL paths when building OTLP/gRPC metric exporter targets from `OTEL_EXPORTER_OTLP_ENDPOINT` and `OTEL_EXPORTER_OTLP_METRICS_ENDPOINT`, while preserving `unix://` and `unix-abstract://` targets; treat `unix-abstract://` endpoints as insecure in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc` and `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#8862) | ||
| - Ignore HTTP(S) paths when deriving gRPC trace exporter endpoints from `OTEL_EXPORTER_OTLP_ENDPOINT` and `OTEL_EXPORTER_OTLP_TRACES_ENDPOINT` in `go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc`. (#8852) | ||
| - Preserve exemplar trace and span IDs in `go.opentelemetry.io/otel/exporters/prometheus` by dropping filtered attribute labels instead of the whole exemplar when the combined exemplar labels would exceed the prometheus client-go limit. |
Contributor
Author
|
Good catch, added the PR number. |
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Summary
Fixes #6718.
prometheus client-go rejects exemplars whose combined label runes exceed
prometheus.ExemplarMaxRunes(128).addExemplarslet that error propagate up fromprometheus.NewMetricWithExemplarsand dropped every exemplar for the data point when the limit was hit, even though the trace and span ID labels alone are well within the limit and are the most valuable part of an exemplar.This checks each exemplar's combined label length against the limit before building the exemplar. When it would exceed the limit, the filtered-attribute-derived labels are dropped and only the trace and span IDs are kept, with a warning logged via
global.Warnso the truncation is visible instead of silent.Test plan
TestExemplarsExceedingLabelLimit, verified it fails without the fix (exemplar dropped entirely) and passes with it (trace/span IDs preserved, filtered attributes dropped).go test ./... -racemake precommit