Metrics API usability: recording time

[jonatan-ivanov]

Recording time values is not a first-class concept in OpenTelemetry Metrics, there is no component that supports this by default but users need to measure time on their own and record it using a ValueRecorder.

Time Unit

Some metrics backends have a preference for a base time unit (e.g. Prometheus expects times in seconds). This preference is a concern for exporting but recording should be possible in any time unit. Without it being a first-class concept, this doesn’t seem possible currently without parsing the String unit to determine if it is a time unit.

Clock abstraction

No clock abstraction currently. It is easy for users to calculate time values incorrectly without a clock abstraction (e.g. using wall time instead of monotonic time)

We touched this topic on the Metrics Workshop, and several people agreed that having such a concept would be useful, we also discussed about multiple ways of doing this (through spans or through a dedicated instrument). Let me cc a few people who I know shared some opinions about the topic:
@shakuzen @ebullient @brian-brazil @bogdandrutu @jmacd @jsuereth @matthiasr @rakyll @RichiH @tomwilkie @alolita

Connected issue: #464