Lazy vs non-Lazy Event APIs about opentelemetry-go

[bogdandrutu]

Lazy events at the end is not necessarily good. For example you force everyone to make these data available in the function that calls end. Also some implementation may want to allow access in real time to these process (what OpenCensus calls zpages active spans).

Another usecase is that you the user to also record a timestamp for these events because they don't happen at the end of the Span.

[bogdandrutu]

My 2 cents here is to eliminate the Event interface and use a concrete type + formatter to avoid allocation when possible and keep that API

[jmacd]

In the OpenTelemetry FinishOptions, each log record has an independent timestamp.

I also support the idea that Event (or AddEvent) should use a concrete type + formatter, it's exactly what I mean when I say "lazy value". Sounds like this will be easy to resolve.

[jmacd]

Today's API reads:

	// AddEvent adds an event to the span.
	AddEvent(ctx context.Context, event event.Event)
	// AddEvent records an event to the span.
	Event(ctx context.Context, msg string, attrs ...core.KeyValue)

I believe we should eliminate one of these. The specification says the method should be named "AddEvent", but we have agreed above in this issue not to use an interface.

Therefore, we should consolidate into one method

   AddEvent(ctx context.Context, msg string, attrs ...core.KeyValue)

and remove the Event interface.