langgraphjs/libs/checkpoint-postgres

@langchain/langgraph-checkpoint-postgres

Implementation of a LangGraph.js CheckpointSaver that uses a Postgres DB.

Usage

import { PostgresSaver } from "@langchain/langgraph-checkpoint-postgres";

const writeConfig = {
  configurable: {
    thread_id: "1",
    checkpoint_ns: ""
  }
};
const readConfig = {
  configurable: {
    thread_id: "1"
  }
};

// you can optionally pass a configuration object as the second parameter
const checkpointer = PostgresSaver.fromConnString("postgresql://...", {
  schema: "schema_name" // defaults to "public"
});

// You must call .setup() the first time you use the checkpointer:
await checkpointer.setup();

const checkpoint = {
  v: 1,
  ts: "2024-07-31T20:14:19.804150+00:00",
  id: "1ef4f797-8335-6428-8001-8a1503f9b875",
  channel_values: {
    my_key: "meow",
    node: "node"
  },
  channel_versions: {
    __start__: 2,
    my_key: 3,
    "start:node": 3,
    node: 3
  },
  versions_seen: {
    __input__: {},
    __start__: {
      __start__: 1
    },
    node: {
      "start:node": 2
    }
  },
  pending_sends: [],
}

// store checkpoint
await checkpointer.put(writeConfig, checkpoint, {}, {});

// load checkpoint
await checkpointer.get(readConfig);

// list checkpoints
for await (const checkpoint of checkpointer.list(readConfig)) {
  console.log(checkpoint);
}

Usage with existing connection pool

import { PostgresSaver } from "@langchain/langgraph-checkpoint-postgres";
import pg from "pg";

// You can use any existing postgres connection pool
// we create a new pool here for the sake of the example
const pool = new pg.Pool({
  connectionString: "postgresql://..."
});

const checkpointer = new PostgresSaver(pool, undefined, {
  schema: "schema_name"
});

await checkpointer.setup();

// ...

Edge & serverless runtimes (Cloudflare Workers, etc.)

PostgresSaver uses node-postgres (pg) under the hood, which opens a raw TCP/TLS connection via Node's net/tls modules. Some serverless/edge runtimes, most notably Cloudflare Workers, do not support raw outbound TCP connections from arbitrary code, so a direct connection (including the initial await checkpointer.setup()) will hang. This is the root cause for issues where the runtime reports that the Worker "had hung and would never generate a response".

This is a database-driver/runtime limitation, not a persistence-flush problem. LangGraph awaits all pending checkpoint writes before invoke()/stream() resolves (see the base checkpoint package README), so as long as you await the run you do not need ctx.waitUntil() to keep the runtime alive for persistence.

To use Postgres checkpointing from Cloudflare Workers, route the connection through Cloudflare Hyperdrive, which exposes a pg-compatible connection string:

// wrangler.toml / wrangler.jsonc must enable `nodejs_compat` and bind a Hyperdrive instance:
//   compatibility_flags = ["nodejs_compat"]
//   [[hyperdrive]]
//   binding = "HYPERDRIVE"
//   id = "<your-hyperdrive-id>"

import { PostgresSaver } from "@langchain/langgraph-checkpoint-postgres";

export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const checkpointer = PostgresSaver.fromConnString(
      env.HYPERDRIVE.connectionString
    );
    // ... compile and `await graph.invoke(...)` here ...
    // Persistence is complete once `invoke`/`stream` resolves.
    return new Response("ok");
  },
};

Alternatively, implement a thin BaseCheckpointSaver on top of an HTTP/WebSocket Postgres driver such as @neondatabase/serverless that is designed for edge runtimes.

Note: standard Node.js, Deno, and Bun deployments are unaffected — PostgresSaver works there out of the box.

Testing

Spin up testing PostgreSQL

docker-compose up -d && docker-compose logs -f

Then use the following connection string to initialize your checkpointer:

const testCheckpointer = PostgresSaver.fromConnString(
  "postgresql://user:password@localhost:5434/testdb"
);