Tail Sampling (dynamically determine if trace should be included or not)

[parmsib]

Describe the feature or potential improvement

From what I can tell, there is no way to implement tail sampling for Langfuse, or at least not with the Langfuse Python SDK.

Motivation

The above linked opentelemetry docs page does a better job of explaining the motivation behind tail sampling than I can, but I'll give a short version below:

It would be very useful to dynamically, i.e. as the traced code is being executed, be able to determine whether a trace should be sent to langfuse or just dropped. One obvious example of this would be to guarantee all traces for failed requests are kept, while still having a sampling rate below 1 to keep costs down.

The way sampling currently works, you can only set a static sampling rate applied to all traces. For some given error that has occurred you only have a chance -- with probability equal to your sampling rate -- of the trace containing the error to have been sent to langfuse. You effectively have to weigh cost of a high sampling rate against the probability of catching crucial errors.

Additional information

No response

[hassiebp]

Thanks for raising this idea! Indeed this is currently not possible with our SDKs. Tail sampling is usually achieved in OpenTelemetry via a collector that is staging all OTEL spans and applies their own sampling rules on the span batch prior to exporting. https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/processor/tailsamplingprocessor