otelcol.exporter.prometheus spams the log with errors #5426
Description
Component(s)
otelcol.exporter.prometheus
What's wrong?
After an upgrade from 1.12.2 to 1.13.0-rc3 otelcol.exporter.prometheus started spamming the logs with an error message added in #5045
It looks like otelcol.exporter.prometheus wants to add metadata with a labelset only containing __name__ while the WAL's new UpdateMetadata implementation uses a full labelset. This means that all calls to UpdateMetadata from otelcol.exporter.prometheus will result in log spam.
Steps to reproduce
Configure otelcol.exporter.prometheus and feed some otel metrics to it.
System information
Linux 6.12.55-74.119.amzn2023.aarch64
Software version
Grafana Alloy v1.13.0-rc3
Configuration
Logs
ts=2026-02-03T18:10:17.56887227Z level=warn msg="failed to write metric family metadata" component_path=/ component_id=otelcol.exporter.prometheus.global metric_name=traces_spanmetrics_duration_milliseconds err="2 errors occurred:\n\t* unknown series when trying to add metadata with SeriesRef: 0 and labels {__name__=\"traces_spanmetrics_duration_milliseconds\"}\n\t* unknown series when trying to add metadata with SeriesRef: 0 and labels: {__name__=\"traces_spanmetrics_duration_milliseconds\"}\n\n"
ts=2026-02-03T18:13:40.931274275Z level=warn msg="failed to write metric family metadata" component_path=/ component_id=otelcol.exporter.prometheus.global metric_name=traces_service_graph_request_server_seconds err="2 errors occurred:\n\t* unknown series when trying to add metadata with SeriesRef: 0 and labels: {__name__=\"traces_service_graph_request_server_seconds\"}\n\t* unknown series when trying to add metadata with SeriesRef: 0 and labels: {__name__=\"traces_service_graph_request_server_seconds\"}\n\n"
Tip
React with 👍 if this issue is important to you.