Confused about label names/values

[John Dexter]

I've been looking at examples in the Java and C++ client libs, and it doesn't mirror my understanding of label rules:

https://github.com/prometheus/client_java#labels

I thought:

1. each metric could have zero or more named labels
2. each label must have a pre-determined set of allowed values
3. when setting a metric value, all label dimensions must be specified from these allowed values

But the examples don't work that way:

Counter calculationsCounter = Counter.build() .name("my_library_calculations_total").help("Total calls.") .labelNames("key").register();

...

  void processThatCalculates(String key) { calculationsCounter.labels(key).inc(); // Run calculations. } }

In this example, I don't see where "key" allowed values are enumerated. I also don't see how labels(key) knows which label it is referring to. I might have multiple labels.

I wish I could find a non-trivial example which shows what the output scrape would look like. Can anyone help?

[Brian Brazil]

On Tue, 6 Oct 2020 at 12:17, John Dexter <john....@jdxsolutions.com> wrote:

I've been looking at examples in the Java and C++ client libs, and it doesn't mirror my understanding of label rules:

https://github.com/prometheus/client_java#labels

I thought:

1. each metric could have zero or more named labels
2. each label must have a pre-determined set of allowed values

This is a should, not a must. Sometimes you just can't know in advance what the label values would be.

 

1. when setting a metric value, all label dimensions must be specified from these allowed values

And accordingly here this is also a should.

 

But the examples don't work that way:

Counter calculationsCounter = Counter.build() .name("my_library_calculations_total").help("Total calls.") .labelNames("key").register();

...

  void processThatCalculates(String key) { calculationsCounter.labels(key).inc(); // Run calculations. } }

In this example, I don't see where "key" allowed values are enumerated. I also don't see how labels(key) knows which label it is referring to. I might have multiple labels.

labels takes a varidic of strings, which matches the order of labels you passed to labelNames.

Brian

 

I wish I could find a non-trivial example which shows what the output scrape would look like. Can anyone help?

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Brian Brazil

www.robustperception.io