Allow passing labels in new/4, add format/2
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michaelklishin
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Currently the extra info is only returned by `seshat:format/1`: it's useful to attach information you might use for Prometheus labels. Previously we used the counter's name as passed to `seshat:new/3` in the place of this label. Attaching extra info is useful for QQs in RabbitMQ for example. They need to attach the queue name and vhost so that info can be exposed to Prometheus.
This will be useful in RabbitMQ to expose Khepri metrics for example: we want to select just Khepri's metrics out of the `ra` group.
A metrics without labels has a name which could
be used as the label value, but it's not clear
what label key should be in this case.
For example, if a metric is declared like this:
seshat:new(Group, ghost, [{foo, 1, counter, "Total foos given"}]),
then what it'd look like in the Prometheus endpoint?
```
foo{...="ghost"} N
```
Rename things to more resemble how Seshat is used in real life.
Refactor to make variable names consistent: * Name sometimes referred to the metric name, and sometimes to the object emiting the metrics; going forward, it's either Id (object) or Name (metric) * counter index was sometimes referred to as Position (now, always Index) * metric help was sometiems referred to as Description (now, always Help) * Fields/FieldSpec/FieldName were used inconsistently (because Fields and FieldSpec can be the same thing); hopefully it's more clear now * counter referece was sometimes Ref and sometimes CRef (now, always CRef)
seshat:text_format/3 produces a binary that contains the text representation of the metrics in the Prometheus exposition format, so that it can be returned as-is by a Prometheus endpoint
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|
Given how much this PR has evolved (barely matches this description), closing this PR. A new one is coming soon |
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These are some changes to make it easier to expose metrics stored in seshat via prometheus. Two changes:
label() :: term()in a newseshat:new/4function. This is exposed inseshat:format/1as the key of thevaluesmap. We can use this in RabbitMQ to attach the queue resource for a QQ to its counter so that we can switch from reading out of thera_metricsETS table to using Ra counters.seshat:new/3uses theNameas the label which means there's no change in behavior for callers usingseshat:new/3.seshat:format/2function to format metrics for only one member of a group. We can use this in RabbitMQ to read and expose Khepri's metrics without scanning the whole ETS table for theragroup.