Metric Requirement Levels for Semantic Conventions
The following metric requirement levels are specified:
All instrumentations MUST emit the metric. A semantic convention defining a Required metric expects that an absolute majority of instrumentation libraries and applications are able to efficiently emit it.
Instrumentations SHOULD emit the metric by default if it’s readily available and can be efficiently emitted. Instrumentations MAY offer a configuration option to disable Recommended metrics.
Instrumentations that decide not to emit
Recommended metrics due to performance, security, privacy, or other consideration by default, SHOULD allow for opting in to emitting them as defined for the
Opt-In requirement level if the metrics are logically applicable.
Instrumentations SHOULD emit the metric if and only if the user configures the instrumentation to do so.
Instrumentation that doesn’t support configuration MUST NOT emit
This attribute requirement level is recommended for metrics that are particularly expensive to retrieve or might pose a security or privacy risk. These should therefore only be enabled deliberately by a user making an informed decision.