LLM costs data storage

[David97]

Describe your question

In each Langfuse trace, I can see that there is information about LLM calling cost.

I attempted to search the Langfuse PostgreSQL for the cost data but I couldn't discover them. Also I don't see them in clickhouse data.

I guess that the Langfuse PostgreSQL only store the unit price of the LLM calls, and those price data are actually caulculated by Langfuse rather than retrieved from database records.

Please correct me if I am wrong. Thank you very much.

Langfuse Cloud or Self-Hosted?

Self-Hosted

If Self-Hosted

No response

If Langfuse Cloud

No response

SDK and integration versions

No response

Pre-Submission Checklist

• I have checked for existing issues/discussions and consulted Langfuse AI.

[inkeep-ai-assistant[bot]]

You're partially correct. In Langfuse v3, cost data is stored in the database, but the storage location changed during the migration from v2 to v3(1).

According to the migration documentation, a cost backfill background migration runs as part of the v3 upgrade(1). This migration "calculate[s] costs for all events and store[s] them in the Postgres database"(1). The documentation specifically notes that "before, those were calculated on read which had a negative impact on read performance"(1).

So in Langfuse v3:

• Cost data is pre-calculated and stored in PostgreSQL (not ClickHouse)
• This is done via a background migration that processes historical data
• Costs are no longer calculated on-the-fly when viewing traces

The cost information you see in traces comes from the PostgreSQL database where it's been pre-computed and stored. If you're not finding the cost data in your PostgreSQL tables, it's possible the background migration hasn't completed yet, or you may need to check the specific tables where cost details are stored alongside the usage data.

📚 Sources:

1. Migrate Langfuse v2 to v3

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