Feedback for “LangChain & LangGraph Integration”

[huangpengjohn]

Why can't langfuse create the trace when I set stream_mode to events in langgraph_sdk?

[dosubot]

Hi @huangpengjohn! I'm Dosu and I’m helping the langfuse-docs team.

There isn't direct documentation about Langfuse trace creation with stream_mode set to "events" in langgraph_sdk. However, Langfuse typically relies on callback handlers or specific event emissions to capture traces. If "stream_mode=events" changes how or when events are emitted—or bypasses the callback mechanism—Langfuse may not receive the necessary data to create a trace.

In related integrations, proper context propagation and manual flushing (using langfuse.flush()) are crucial, especially in short-lived or serverless environments. It's worth checking if your callback handlers are still being invoked in "events" mode and whether manual flushing helps. If possible, try an alternative stream mode to see if traces are created as expected. This may be an undocumented limitation or a feature gap in the current integration approach. For more on integration nuances and context management, see this discussion.

To reply, just mention @dosu.

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[huangpengjohn]

@hassiebp interesting, when I set stream_mode to "events" or to a list that contains "events", there are no traces in langfuse, but it works normally when I set stream_mode to "messages" or "values", Is this a bug?