Inconsistent metric deduplication in Otel2PrometheusConverter

[nluk]

Describe the bug
Prometheus MetricSnapshots constructor throws because of duplicated metric names. This is a part of the Otel2PrometheusConverter::convert call.

An Exception occurred while scraping metrics: java.lang.IllegalArgumentException: logback_events: duplicate metric name
	at io.prometheus.metrics.model.snapshots.MetricSnapshots.<init>(MetricSnapshots.java:43)
	at io.opentelemetry.exporter.prometheus.Otel2PrometheusConverter.convert(Otel2PrometheusConverter.java:112)
	at io.opentelemetry.exporter.prometheus.PrometheusMetricReader.collect(PrometheusMetricReader.java:56)
	at io.prometheus.metrics.model.registry.MultiCollector.collect(MultiCollector.java:26)
	at io.prometheus.metrics.model.registry.PrometheusRegistry.scrape(PrometheusRegistry.java:72)
	at io.prometheus.metrics.exporter.common.PrometheusScrapeHandler.scrape(PrometheusScrapeHandler.java:112)
	at io.prometheus.metrics.exporter.common.PrometheusScrapeHandler.handleRequest(PrometheusScrapeHandler.java:53)
	at io.prometheus.metrics.exporter.httpserver.MetricsHandler.handle(MetricsHandler.java:43)
	at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:95)
	at jdk.httpserver/sun.net.httpserver.AuthFilter.doFilter(AuthFilter.java:82)
	at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:98)
	at jdk.httpserver/sun.net.httpserver.ServerImpl$Exchange$LinkHandler.handle(ServerImpl.java:851)
	at jdk.httpserver/com.sun.net.httpserver.Filter$Chain.doFilter(Filter.java:95)
	at jdk.httpserver/sun.net.httpserver.ServerImpl$Exchange.run(ServerImpl.java:818)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)

Steps to reproduce
Create two MetricData objects with different names, that resolve to the same prometheusName and run convert.

Testcase to reproduce the error: main...nluk:opentelemetry-java:bug/prometheus-converter-duplicate-metric-name

What did you expect to see?

Hard to say really. Metrics of the same type may be merged, but the fact that there are two competing metrics a.b and a_b might indicate a misconfiguration.

What did you see instead?

The Otel2PrometheusConverter::putOrMerge method uses snapshot.getMetadata().getName() as a unique map key. So metric.name and metric_name are two separate entries.

Prometheus compares sorted snapshot.getMetadata().getPrometheusName() link to find collisions. This means that metric.name and metric_name are both represented as metric_name, and a collision is detected.

What version and what artifacts are you using?
Artifacts: aws-opentelemetry-agent 1.32.1, so opentelemetry 1.32.1 link that targets otel-sdk 1.34.1

Environment
Compiler: Temurin-17.0.5+8
OS: Ubuntu 22.04

[jack-berg]

Prometheus compares sorted snapshot.getMetadata().getPrometheusName() link to find collisions. This means that metric.name and metric_name are both represented as metric_name, and a collision is detected.

I think this getName vs. getPrometheusName is the key bit here. Its an oversight on our part to use getName for the keys of our map. Opening a PR to adjust it to use getPrometheusName everywhere.

But this won't completely solve the problem. Its still possible that my.metric and my_metric have overlapping series. I.e. both might have a series with attributes {key=a}. If this occurs, then the prometheus client will generate an error. I don't think Otel2PrometheusConverter should be responsible for this merging of series. Instead, if a user encounters this, they should use views to rename one of my.metric or my_metric such that the conflict doesn't occur.