Manual transaction handling not instrumenting spans correctly

[cmanallen]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

2.22.0

Steps to Reproduce

import sentry_sdk

sentry_sdk.init(dsn=DSN, debug=True, traces_sample_rate=1)

@sentry_sdk.trace
def test():
    return 1 + 1

transaction = sentry_sdk.start_transaction(
    name="replays.consumer.process_recording",
    op="replays.consumer",
)

test()

transaction.finish()

Expected Result

A trace that looks like this:

https://sentry-sdks.sentry.io/discover/trace/1b95c2cc910b434ea3f98a4b957c7c87/?dataset=transactions&field=title&field=project&field=user.display&field=timestamp&name=All%20Errors&node=txn-6ab2c26430f746fc860e615275f8ae49&project=4508876404162560&query=&queryDataset=transaction-like&sort=-timestamp&source=discover&statsPeriod=5m&timestamp=1740434501&yAxis=count%28%29

Actual Result

A trace that looks like this:

https://sentry-sdks.sentry.io/discover/trace/412b2b91a64047a8884b6b46cf1585ca/?dataset=transactions&field=title&field=project&field=user.display&field=timestamp&name=All%20Errors&node=txn-6c3772f93adf4e96900f5f5aa9fff341&project=4508876404162560&query=&queryDataset=transaction-like&sort=-timestamp&source=discover&statsPeriod=5m&timestamp=1740434513&yAxis=count%28%29

[cmanallen]

This is how I fixed it:

import sentry_sdk

sentry_sdk.init(dsn=DSN, debug=True, traces_sample_rate=1)

@sentry_sdk.trace
def test():
    return 1 + 1

with sentry_sdk.start_transaction(
    name="replays.consumer.process_recording", op="replays.consumer"
):
    test()

The context manager works but transaction start() and finish() do not.

[cmanallen]

Not sure if this is an SDK bug or just a misunderstanding on my part. Is start_transaction only supposed to be called as a context manager?

[antonpirker]

Yes, start_transaction() should always be called with a context manager.

[sentrivana]

start_transaction creates the transaction, but it is not actually set on the scope; the scope management happens in the __enter__/__exit__ of the context manager. Without the transaction being set on the scope the transaction will not be considered active.

So the two options are either to use the context manager (with start_transaction(...):, or txn = start_transaction(...); txn.__enter__(); txn.__exit__()), or start_transaction alone and then set the transaction on the scope manually. (We can improve the docs on this.)

[cmanallen]

@antonpirker @sentrivana What's interesting is that this was working previously. See my PR: https://github.com/getsentry/sentry/pull/85447/files#diff-c9170e96111ac9ba2c4657aaeef8281aad6254fb7bcbacec272b2a2c8eca0355L106-L114

[cmanallen]

Ah never mind I call with with transaction.start_child(...) later on.

[antonpirker]

As this is resolved, I am closing this issue.