Prometheus endpoint does not provide metric name

[jmesnil]

While playing with the jvm.uptime metric, I noticed that the Prometheus endpoint does not contain the actual name of the metric.

$ curl http://127.0.0.1:9990/metrics/base/
...
# HELP base:jvm_uptime_seconds Displays the start time of the Java virtual machine in milliseconds. This attribute displays the approximate time when the Java virtual machine started.
# TYPE base:jvm_uptime_seconds gauge
base:jvm_uptime_seconds 3.277E-4
...

When I tried to get the metric only for `jvm.uptime, I tried the name from the previous result:

$ curl http://127.0.0.1:9990/metrics/base/jvm_uptime_seconds
Metric base/jvm_uptime_seconds not found
$ curl http://127.0.0.1:9990/metrics/base/jvm_uptime
Metric base/jvm_uptime not found

It turns ou that I need to use the original metric name jvm.uptime (which is obvious in retrospect):

$ curl http://127.0.0.1:9990/metrics/base/jvm.uptime
# HELP base:jvm_uptime_seconds Displays the start time of the Java virtual machine in milliseconds. This attribute displays the approximate time when the Java virtual machine started.
# TYPE base:jvm_uptime_seconds gauge
base:jvm_uptime_seconds 1.43104E-4

However there is no way to know the actual metric name from the Prometheus output itself as the metrics/base endpoint only mentions jvm_uptime_seconds and never jvm.uptime.

Could we improve somehow the Prometheus export format so that it is possible to drill down the metric from their scope without having to mentally convert the metric name from MicroProfile to the Prometheus one according to the spec (section 3.2.1. Translation rules for metric names)?

[rsvoboda]

@kenfinnigan can you look into this or assign appropriate person, please ?

[kenfinnigan]

@rsvoboda It will be looked at when we've scheduled the work

[pilhuhn]

@jmesnil I think I like the idea, can you please open an issue in @eclipse/microprofile-metrics ?
While the spec does not directly talk about this, it is obvious from the OpenMetrics format, that the # HELP line can not just replace the name in OM-format with the original one.

We could just append the original name in parens at the end of the description, but it would not exactly follow the spec ("luckily" there are no tests for the # HELP line :)

A patch should be relatively straight-forward as https://github.com/smallrye/smallrye-metrics/blob/master/implementation/src/main/java/io/smallrye/metrics/exporters/PrometheusExporter.java#L295 is creating the # HELP line and the original metric name should be in the key.