Meter implementations MUST return an error when multiple instruments are registered by the same name

[codeboten]

As per spec:

Metric instrument names belong to a namespace, established by the the associated Meter instance. Meter implementations MUST return an error when multiple instruments are registered by the same name.

https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/metrics/api.md#instrument-naming-requirements

[srikanthccv]

@codeboten I would like to pick this up. Help me if I am understanding this correctly. Meter instance will be used to create multiple instrumentation using different functions such as create_counter, create_updowncounter and create_valuerecorder etc.. when user creates different instruments with same name, Meter should throw an error saying something like multiple instruments can't registered by the same name.

[lzchen]

@lonewolf3739
I believe this is the correct understanding.

[aabmass]

Related discussion on potentially just returning the existing instrument when this happens: open-telemetry/opentelemetry-specification#1046

[srikanthccv]

From Spec

The OpenTelemetry SDK is responsible for ensuring that an individual Meter implementation cannot report multiple instruments with the same name and different definitions. To accomplish this, SDKs MUST reject duplicate registration of an instrument when another instrument has already been registered with same metric name to the same named Meter.

Does the term definition here mean the tuple (name, desc, unit)?

The requirement applies even for attempts to register an identical instrument definition.

Does this mean regardless of definition sdk must reject registration if another instrument has been registered with same name?

Was there any further discussion on returning the existing instrument in spec SIG or similar meetings?

[srikanthccv]

One another thing clear is names should be case insensitive.

[lzchen]

@lonewolf3739
I would ask in the issue that @aabmass linked to.