Why the Prometheus exporter uses start_ts as timestamp and not end_ts

[ondra-novak]

opentelemetry-cpp/exporters/prometheus/src/exporter_utils.cc

Line 53 in b8b715f

auto time = metric_data.start_ts.time_since_epoch();

Why the Prometheus exporter uses start_ts as timestamp and not end_ts?

As I understand, start_ts defines point when measuring started, and end_ts when ends. According to example in specification, start_ts should be always same, because Prometheus use cumulative temporality and thus starting time should equal to start of the program.

Am I wrong?

https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/img/model-cumulative-sum.png

Associated error message (Prometheus log]

level=warn ts=2022-12-14T15:10:11.093Z caller=scrape.go:1167 component="scrape manager" scrape_pool=example target=http://localhost:9464/metrics msg="Error on ingesting samples with different value but same timestamp" num_dropped=15

[github-actions]

This issue was marked as stale due to lack of activity.

[marcalff]

Closing as a duplicate of:

• [EXPORTER] Prometheus: Error on ingesting samples with different value but same timestamp #2125

for which there is a PR already.