Description
Component(s)
exporter/prometheusremotewrite
Is your feature request related to a problem? Please describe.
This issue is similar to #19153; currently the Prometheus Remote Write exporter only supports cumulative exponential histograms and drops delta exponential histograms (see #17370 and the related spec guidance added on open-telemetry/opentelemetry-specification/pull/3079).
Describe the solution you'd like
Delta exponential histograms are accumulated into a cumulative exponential histogram and then the cumulative exponential histogram to Prometheus native histogram conversion logic is applied. To merge the exponential histograms, the lowest scale among them should be used.
Describe alternatives you've considered
We could have this functionality on a separate processor. The proposed solution for #19153 seems to add functionality in the exporter itself, so I went with that, but I also see advantages on having a separate processor for this.
Additional context
This needs a change in the specification, since it currently says:
OpenTelemetry Exponential Histogram metrics with the delta aggregation temporality are dropped.
It would have to be changed to say
OpenTelemetry Exponential Histograms with Delta aggregation temporality SHOULD be aggregated into a Cumulative aggregation temporality and follow the logic above, or MUST be dropped.
similar to what we say for OpenTelemetry Histograms with Delta aggregation temporality.
This issue is specific to the PRW exporter since the Prometheus exporter does not support exponential histograms yet, but I tagged it with exporter/prometheus since we should take this exporter also into account.