[java] Tracing without Performance

[smeubank]

Problem Statement

It should be possible that tracing information is propagated from/to incoming/outgoing HTTP requests even if performance is disabled and thus no transactions/spans are available.

Solution Brainstorm

See the PHP implementation as a template: getsentry/sentry-php#1516

[smeubank]

to check with @markushi if he is working on this for android

[adinauer]

to check with @markushi if he is working on this for android

Not yet. I'll involve him on PRs.

[adinauer]

Questions that came up + answers:

1. For incoming requests we want to either continueTrace from incoming headers or if none are present create a new PropagationContext with random traceId and spanId, correct?
   Answer: Yes

2. If there's no incoming headers on the request do we even create a DSC and attach baggage header to outgoing requests?
   Answer: Yes, initially in this case DSC (Baggage for Java) is null on PropagationContext and created when an outgoing request is performed (e.g. HTTP request by user or a request to Sentry). * If there's no transaction.

3. There's other places where we start transactions that don't originate from incoming requests but some user interaction / system call on Android. Do we create a new PropagationContext in all those spots where we'd create a transaction if performance was enabled?
   Answer: If the button click (or similar) creates a new TraceID today when using performance, it should also create a new TraceID when performance is off, so a new PropagationContext

4. OTEL: Is there ever a scenario where users would add our OTEL integration but have performance disabled? Does that mean we should still extract and attach headers in our OTEL integration?
   Answer: We'll ignore this for now as it seems rather unlikely.

5. Should tracesSampling be considered.
   Answer: Yes, we shouldn't attach headers or trace context if it's set to false. We can think about removing the option in an upcoming major.

6. For context keyed trace on envelope header do we simply check if performance is enabled then try to find a transaction on scope and use its TraceContext and if performance is disabled we use PropagationContext on the scope?
   Answer: Yes. Also: "In order to make Dynamic Sampling work, it’s crucial that the correct data is in the envelope header. So if there is a transaction going to be sent to Sentry, you should never fallback to the PropagationContext to generate the header values."