Clarify that continue_trace does not start transaction

[szokeasaurusrex]

Core or SDK?

Platform/SDK

Which part? Which one?

Python

Description

The documentation should clarify the fact that while continue_trace creates transactions, it does not start them. For instance, if one has the following code:

with sentry_sdk.continue_trace(sampled=True, ...):
    ...  # do something ...

The generated transaction does not get sent to Sentry (despite the sampled=True) because the transaction was not started with start_transaction.

Suggested Solution

The above sample can be corrected as follows:

transaction = sentry_sdk.continue_trace(sampled=True, ...)
with sentry_sdk.start_transaction(transaction):
    ...  # do something ...

This way, the transaction is continued from the trace, and it gets started properly.

---

We should include an example like the above somewhere in the docs, and also explain that transactions must always be started with start_transaction. A good place to do this might be here.

Making these changes will help avoid the confusion that led to getsentry/sentry-python#2990 being opened, even though the behavior described in that issue is expected.