Improve windowed "max" documentation about micrometer

[jonatan-ivanov]

Practically, currently I see Spring Boot outputs the following metrics:
http.server.requests histogram (who has "max");
http.server.requests.max gauge.
It's not easily clear which one means what and why there are two. For example, in Grafana I just see one of them, because probably one overrides the other.

I'm not sure what is going on here, you are saying that you see two maxes but then you say you only see one? Which registry are you using?
If this is Prometheus, there should be only one max (a gauge), the histogram does not have a max and there are no overrides.

It would be great if docs provided practical example (something like saying "for example in Spring, http.server.requests.max is a time windowed max...").

Micrometer does not depend on Spring, it does not know about http.server.requests.max, that one is Spring-relates so it should live in the Spring docs (afaik it mentions it). The Micrometer docs do mention that max is a time-window max.

As I understand, Micrometer doesn't specify an exact list of metrics with their meanings (unlike OpenTelemetry), so because it's Spring who actually outputs those, it could be more issue of Spring docs that don't explain it (currently, doesn't explain anything besides the name: https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#actuator.metrics.supported.spring-mvc), so let me know if you think it's an issue for them instead, but since Micrometer mentioned already windowed max in the docs, since it provides reference implementation for some other components, and since the end goal is making it clear for users anyway, it could be worth explaining in Micrometer docs.

http.server.requests is created by Spring Framework, you should look into those docs not Spring Boot.

It's not really clear to me what doc improvements you want but please feel free to add more details to this issue and/or open a PR, we are happy to review it.

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