opentelemetry-cpp: Every metric data has _field "gauge" instead of "counter"

Question

We used opentelemetry-cpp v1.8.1 (metrics for now) previously on a project. Everything worked fine regarding metadata present in influxdb. Metric data that came from UpDownCounter had _field tag "counter" which was according to our expectations. Recently we witched to 1.11.0. I did not make any changes in the code, but now each metric has _field tag that shows "gauge" even if original metricInstrument is of UpDownCounter type. Does anybody know what can be the reason of such a behavior? Is there a possibility to fix this? Thanks in advance!

I was trying to debug otel library locally, made it to the place where json is formed in OtlpHttpClient::createSession(...). Observing that string does not help to find a place where metricData contains something like "counter" or "gauge".

Answer 1

For something called an UpDowncounter, only the gauge type is appropriate. Compare the following definitions from the OpenMetrics spec:

Gauge: Gauges MAY increase, decrease, or stay constant over time.
Counter: MUST be monotonically non-decreasing over time, starting from 0. MAY reset to 0. If present, the corresponding Created time MUST also be set to the timestamp of the reset.

I think the relevant change is this line from the 1.10 changelog:

[EXPORTER] set is_monotonic only for instrument type kCounter #2171