Why is the "http_server_active_requests" metric no longer emitted ? (i.e. moved to experimental category)

[pcabot]

Hi,
Great work by the way for the java instrumentation !

My team was using the http_server_active_requests metric in the Java agent 1.17, but then after upgrading to 1.32 we found out that the metric was not longer emitted as part of the standard config. After reading the release notes, we found out that it was possible to re-enable it by setting the OTEL_INSTRUMENTATION_HTTP_SERVER_EMIT_EXPERIMENTAL_METRICS: true environment variable, but we are not sure of the impact.

I have 2 questions related to the topic :

1. Why was the http_server_active_requests metric moved into the experimental category ? Is there a plan to put it back as part of the standard config ? I did not find the reason in the original issue.
2. What does experimental metrics mean, i.e. is it because those metrics are not stable and might produce incorrect results or is it because that flag can cause general instability issues at the agent level and that flag should not be used in prod ?

Thanks !

[laurit]

Why was the http_server_active_requests metric moved into the experimental category ? Is there a plan to put it back as part of the standard config ? I did not find the reason in the original #9011.

Our convention is that by default we only emit telemetry that is specified in the open telemetry semantic conventions This metrics was not included when the http semantic conventions were declared stable. We will start emitting it by default once the specification declares it stable.

What does experimental metrics mean, i.e. is it because those metrics are not stable and might produce incorrect results or is it because that flag can cause general instability issues at the agent level and that flag should not be used in prod ?

Experimental means that it is not stable in the spec, there may be breaking changes in the telemetry (such as removal of attributes etc.). Experimental does not indicate that the metric could produce incorrect values or affect the stability of the application, such behavior would be considered a bug.

[pcabot]

Thanks for the explanation !