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Prefer the name "Counter" as opposed to "Cumulative".
Informally speaking, it seems that OpenTelemetry community members would prefer to call Cumulative metric instruments "Counters". During conversation (e.g., in the 8/21 working session), this has become clear.
Counter is a noun, like the other kinds Gauge and Measure. Cumulative is an adjective, so while "Cumulative instrument" makes sense, it describes a "Counter".
This will eliminate the cognitive cost of mapping "cumulative" to "counter" when speaking about these APIs.
This is the term used for a cumulative metric instrument, for example, in Statsd and Prometheus.
However, we have identified important sub-cases of Counter that are treated as follows. Counters have an option:
- True-cumulative Counter: By default,
Add()arguments must be >= 0. - Bi-directional Counter: As an option,
Add()arguments must be +/-0.
Gauges are sometimes used to monitoring non-descending quantities (e.g., cpu usage), as an option:
- Bi-directional Gauge: By default,
Set()arguments may by +/- 0. - Uni-directional Gauge: As an option,
Set()arguments must change by >= 0.
Uni-directional Gauge instruments are typically used in metric Observer callbacks where the observed value is cumulative.
Other ways to describe the distinction between true-cumulative and bi-directional Counters are:
- Additive (vs. Cumulative)
- GaugeDelta (vs. Gauge)
It is possible that reducing all of these cases into the broad term "Counter" creates more confusion than it addresses.
Simply replace every "Cumulative" with "Counter", then edit for grammar.
In a survey of existing metrics libraries, Counter is far more common.