how to customize trace id when using callback handler in langchain integration

[shawnzhu]

When following the Customize IDs section, it supports changing trace id for a function decorated with @observe().

How to do the same thing without the decorator?

[dosubot[bot]]

Hey there, @shawnzhu! I'm here to help you with any bugs, questions, or contributions you have while waiting for a human maintainer. Let's dive in and solve this together!

To customize the trace ID when using a callback handler in Langchain integration without using the @observe() decorator, you can pass the userId as a parameter to the CallbackHandler constructor:

import { CallbackHandler } from "langfuse-langchain/src/callback";

// Create a callback handler with a custom user ID
const langfuseHandler = new CallbackHandler({ userId: "your-user-id", sdkIntegration: "your-sdk-integration" });

You can then use this handler in your Langchain invocations:

chain.invoke({ person: "obama", language: "spanish" }, { callbacks: [langfuseHandler] });

This approach allows you to set a custom trace ID without using the @observe() decorator ^{[1][2][3][4][5]}.

To continue talking to Dosu, mention @dosu.

[shawnzhu]

it could not customize trace id like this when using the low level API.

[shawnzhu]

I figured it out by customizing run_id of a Langchain runnable, which is later used as trace id.

from langfuse.callback import CallbackHandler

run_id = uuid4()
langfuse_handler = CallbackHandler();
agent.invoke({"input": input}, config={"callbacks":[langfuse_handler], "run_id": run_id})

Notice that it will also changed the run_id of this langchain runnable as well.

[marcklingen]

this is great! alternatively, you could use the low-level sdk to create a trace and get a langchain callback handler for it:

# Intialize Langfuse Client
from langfuse import Langfuse
langfuse = Langfuse()
 
# Get Langchain handler for a trace
trace = langfuse.trace()
langfuse_handler_trace = trace.get_langchain_handler(
   update_parent=True # add i/o to trace itself as well
)
 
# Add Langfuse handler as callback (classic and LCEL)
chain.invoke({"input": "<user_input>"}, config={"callbacks": [langfuse_handler_trace]})

[marctorsoc]

FWIW, this works too

langfuse_handler = CallbackHandler();
agent.invoke({"input": input}, config={"callbacks":[langfuse_handler], "run_name": specific_name_for_this_input})

[ilkersigirci]

@marcklingen @jannikmaierhoefer In Python SDK v3, run_id and trace_id seems to be different. Is there any way to programmatically get trace_id of the langfuse.langchain.CallbackHandler ?

[fhoering]

Also wondering how to do this. In our case we have two disconnected graphs. And it would be good to be able to inject the existing trace id to be able to keep everything in the same trace.

The trace_context doesn't seem to be part of the CallbackHandler and just reusing the same CallbackHandler instance from a module across async context doesn't seem to work.

[fhoering]

I made some tests but was only able to achieve this by patching the call back handler.
langfuse/langfuse-python#1419
@hassiebp

[hassiebp]

You can access the last trace id via handler.last_trace_id after you chain invocation

[fhoering]

@hassiebp handler.last_trace_id doesn't seem to be preserved across async contexts as per #8216

[mukeshkdangi]

langfuse/langfuse-python#1419

this won't help in multi user /concurrent system

[klaasmeinke]

In langfuse SDK v3, you can now set the langfuse trace id like this:

import uuid
from langfuse.langchain import CallbackHandler

trace_id = str(uuid.uuid4()).replace("-", "")
handler = CallbackHandler(trace_context={"trace_id": trace_id})

You can also generate a trace id from any value using langfuse.create_trace_id(seed="your id") as is recommended in the docs.

[mukeshkdangi]

ideally CallbackHandler should be shared across the app or sessions so if we share means we can't set the trace_id manually. i wanted to set the trace_id so that i can use those trace_ids to update the traces and user feedbacks