Postgres adapter

How it works

The Postgres adapter relies on the NOTIFY and LISTEN commands.

Every packet that is sent to multiple clients (e.g. io.to("room1").emit() or socket.broadcast.emit()) is:

• sent to all matching clients connected to the current server
• if the packet contains binary data or is above the 8000 bytes limit, the packet is:
  • encoded with msgpack and inserted in an auxiliary table
  • the row ID is sent within a NOTIFY command
  • this row ID is received by the other Socket.IO servers of the cluster, which query the table, decode the packet and then broadcast it to their own set of connected clients
• else, the packet is simply sent within a NOTIFY command and received by the other Socket.IO servers of the cluster

The source code of this adapter can be found here.

Installation

npm install @socket.io/postgres-adapter pg

For TypeScript users, you might also need @types/pg.

Usage

const { Server } = require("socket.io");const { createAdapter } = require("@socket.io/postgres-adapter");const { Pool } = require("pg");
const io = new Server();
const pool = new Pool({  user: "postgres",  host: "localhost",  database: "postgres",  password: "changeit",  port: 5432,});
pool.query(`  CREATE TABLE IF NOT EXISTS socket_io_attachments (      id          bigserial UNIQUE,      created_at  timestamptz DEFAULT NOW(),      payload     bytea  );`);
io.adapter(createAdapter(pool));io.listen(3000);

Options

Name	Description	Default value
uid	the ID of this node	a random ID
channelPrefix	the prefix of the notification channel	socket.io
tableName	the name of the table for payloads over the 8000 bytes limit or containing binary data	socket_io_attachments
payloadThreshold	the threshold for the payload size in bytes	8000
requestsTimeout	the timeout for inter-server requests such as fetchSockets() or serverSideEmit() with ack	5000
heartbeatInterval	the number of ms between two heartbeats	5000
heartbeatTimeout	the number of ms without heartbeat before we consider a node down	10000
cleanupInterval	the number of ms between two cleanup queries	30000

Common questions

• Do I still need to enable sticky sessions when using the Postgres adapter?

Yes. Failing to do so will result in HTTP 400 responses (you are reaching a server that is not aware of the Socket.IO session).

More information can be found here.

• What happens when the Postgres server is down?

In case the connection to the Postgres server is severed, the packets will only be sent to the clients that are connected to the current server.

Emitter

The Postgres emitter allows sending packets to the connected clients from another Node.js process:

Installation

npm install @socket.io/postgres-emitter pg

Usage

const { Emitter } = require("@socket.io/postgres-emitter");const { Pool } = require("pg");
const pool = new Pool({  user: "postgres",  host: "localhost",  database: "postgres",  password: "changeit",  port: 5432,});
const emitter = new Emitter(pool);
setInterval(() => {  emitter.emit("ping", new Date());}, 1000);

Please refer to the cheatsheet here.