Why does this subscriber drop events that don't have spans?

[Kinrany]

The most simple setup with tracing_subscriber::fmt prints events that are logged without a span. This subscriber doesn't, I don't quite understand why. Are the tracing models different between tracing and OpenTelemetry somehow? Am I just doing it wrong if I'm getting this result?

[hawkw]

My understanding is that OpenTelemetry does not have a concept of log events that are not part of a span. Perhaps @jtescher can confirm this?

[davidbarsky]

They somewhat do in the form of https://opentelemetry.io/docs/specs/otel/logs/, but to the best my limited knowledge, they are disjoint from SpanEvents.

[jtescher]

Yes you are both correct. The otel trace signal does not have events outside of spans, nor do distributed tracing systems like jaeger and zipkin support these types of events.

The otel logs signal does have this concept but it is not implemented in this crate. There is some work in progress to experiment with adding this support in https://github.com/open-telemetry/opentelemetry-rust/tree/main/opentelemetry-appender-tracing.