Troubleshooting

We expect most users of the Python SDK not to run into any of the problems documented here.

Use the information in this page to help answer these questions:

• "What do I do if scope data is leaking between requests?"
• "What do I do if my transaction has nested spans when they should be parallel?"
• "What do I do if the SDK has trouble sending events to Sentry?"

Addressing Concurrency Issues

The short answer to the first two questions: make sure your contextvars work and that your isolation scope was cloned for each concurrency unit.

Python supports several distinct solutions to concurrency, including threads and coroutines.

The Python SDK does its best to figure out how contextual data such as tags set with sentry_sdk.set_tags is supposed to flow along your control flow. In most cases it works perfectly, but in a few situations some special care must be taken. This is specially true when working with a code base doing concurrency outside of the provided framework integrations.

The general recommendation is to have one isolation scope per "concurrency unit" (thread/coroutine/etc). The SDK ensures every thread has an independent scope via the ThreadingIntegration. If you do concurrency with asyncio coroutines, make sure to use the AsyncioIntegration which will clone the correct scope in your Tasks.

The general pattern of usage for creating a new isolation scope is:

with sentry_sdk.isolation_scope() as scope:
    # In this block scope refers to a new fork of the original isolation scope,
    # with the same client and the same initial scope data.

See the Threading section for a more complete example that involves forking the isolation scope.

Context Variables vs Thread Locals

The Python SDK uses thread locals to keep contextual data where it belongs. There are a few situations where this approach fails.

Read along if you cannot figure out why contextual data is leaking across HTTP requests, or data is missing or popping up at the wrong place and time.

Python 2: Thread Locals and gevent

If the SDK is installed on Python 2, there is not much else to use than the aforementioned thread locals, so the SDK will use just that.

Code that uses async libraries such as twisted is not supported in the sense that you will experience context data leaking across tasks/any logical boundaries, at least out of the box.

Code that uses more "magical" async libraries such as gevent or eventlet will work just fine provided those libraries are configured to monkeypatch the stdlib. If you are only using those libraries in the context of running gunicorn that is the case, for example.

Python 3: Context Variables or Thread Locals

Python 3 introduced asyncio, which, just like Twisted, had the problem of not having any concept of attaching contextual data to your control flow. That means in Python 3.6 and lower, the SDK is not able to prevent leaks of contextual data.

Python 3.7 rectified this problem with the contextvars stdlib module which is basically thread locals that also work in asyncio-based code. The SDK will attempt to use that module instead of thread locals if available.

For Python 3.6 and older, install aiocontextvars from PyPI which is a fully-functional backport of contextvars. The SDK will check for this package and use it instead of thread locals.

Context Variables vs gevent/eventlet

If you are using gevent (older than 20.5) or eventlet in your application and have configured it to monkeypatch the stdlib, the SDK will abstain from using contextvars even if it is available.

The reason for that is that both of those libraries will monkeypatch the threading module only, and not the contextvars module.

The real-world usecase where this actually comes up is if you're using Django 3.0 within a gunicorn+gevent worker on Python 3.7. In such a scenario the monkeypatched threading module will honor the control flow of a gunicorn worker while the unpatched contextvars will not.

It gets more complicated if you're using Django Channels in the same app, but a separate server process, as this is a legitimate usage of asyncio for which contextvars behaves more correctly. Make sure that your channels websocket server does not import or use gevent at all (and much less call gevent.monkey.patch_all), and you should be good.

Even then there are still edge cases where this behavior is flat-out broken, such as mixing asyncio code with gevent/eventlet-based code. In that case there is no right, static answer as to which context library to use. Even then gevent's aggressive monkeypatching is likely to interfere in a way that cannot be fixed from within the SDK.

This issue has been fixed with gevent 20.5 but continues to be one for eventlet.

Network Issues

Your SDK might have issues sending events to Sentry. In case of errors and tracing data, this manifests as errors and transactions missing in Sentry. In case of cron monitors, you might be seeing crons marked as timed out in Sentry when you know they've run successfully. The SDK itself might be logging errors about the connection getting reset or the server closing the connection without response.

If you experience this, try turning on the keep-alive configuration option, available in SDK versions 1.43.0 and up.

import sentry_sdk

sentry_sdk.init(
    # your usual options
    keep_alive=True,
)

If you need more fine-grained control over the behavior of the socket, check out socket-options.