POSTGRES_URI_CUSTOM is ignored by LangGraph runtime; runtime always falls back to in-memory

LangSmith Product Help
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1

I’m trying to configure LangGraph to use a custom PostgreSQL database for persistence, based on the documented environment variable POSTGRES_URI_CUSTOM.

According to the docs:
https://docs.langchain.com/langsmith/env-var#postgres-uri-custom

Specify POSTGRES_URI_CUSTOM to use a custom Postgres instance instead of one provisioned by the platform.

However, even when POSTGRES_URI_CUSTOM is set correctly, LangGraph continues to start with the in-memory runtime.

Example log:

Using langgraph_runtime_inmem
Starting In-Memory runtime with langgraph-api=0.5.16

This happens consistently in local development (langgraph dev / API server).

2

Yes the dev server uses the in-mem “persistence” layer. Setting a postgres env var would have no effect.

You’ll have to use langgraph up to use the postgres persistence implementation, at which point you can customize the URI.