node-postgres

Non-blocking PostgreSQL client for node.js. Pure JavaScript and optional native libpq bindings.

$ npm install pg

There are 3 ways of executing queries

1. Passing the query to a pool
2. Borrowing a client from a pool and executing the query with it
3. Obtaining an exclusive client and executing the query with it

It is recommended to pass the query to a pool as often as possible. If that isn't possible, because of long and complex transactions for example, borrow a client from a pool. Just remember to initialize the pool only once in your code so you maximize reusability of connections.

If you're working on something like a web application which makes frequent queries you'll want to access the PostgreSQL server through a pool of clients. Why? For one thing, there is ~20-30 millisecond delay (YMMV) when connecting a new client to the PostgreSQL server because of the startup handshake. Furthermore, PostgreSQL can support only a limited number of clients...it depends on the amount of ram on your database server, but generally more than 100 clients at a time is a very bad thing. ™️ Additionally, PostgreSQL can only execute 1 query at a time per connected client, so pipelining all queries for all requests through a single, long-lived client will likely introduce a bottleneck into your application if you need high concurrency.

With that in mind we can imagine a situation where you have a web server which connects and disconnects a new client for every web request or every query (don't do this!). If you get only 1 request at a time everything will seem to work fine, though it will be a touch slower due to the connection overhead. Once you get >100 simultaneous requests your web server will attempt to open 100 connections to the PostgreSQL backend and 💥 you'll run out of memory on the PostgreSQL server, your database will become unresponsive, your app will seem to hang, and everything will break. Boooo!

Good news: node-postgres ships with built in client pooling. Client pooling allows your application to use a pool of already connected clients and reuse them for each request to your application. If your app needs to make more queries than there are available clients in the pool the queries will queue instead of overwhelming your database & causing a cascading failure. 👍

node-postgres uses pg-pool to manage pooling. It bundles it and exports it for convenience. If you want, you can require('pg-pool') and use it directly - it's the same as the constructor exported at pg.Pool.

It's highly recommended you read the documentation for pg-pool.

Here is an up & running quickly example

For more information about config.ssl check TLS (SSL) of nodejs

Let's create a pool in ./lib/db.js which will be reused across the whole project

const pg = require('pg');

// create a config to configure both pooling behavior
// and client options
// note: all config is optional and the environment variables
// will be read if the config is not present
var config = {
  user: 'foo', //env var: PGUSER
  database: 'my_db', //env var: PGDATABASE
  password: 'secret', //env var: PGPASSWORD
  host: 'localhost', // Server hosting the postgres database
  port: 5432, //env var: PGPORT
  max: 10, // max number of clients in the pool
  idleTimeoutMillis: 30000, // how long a client is allowed to remain idle before being closed
};

//this initializes a connection pool
//it will keep idle connections open for 30 seconds
//and set a limit of maximum 10 idle clients
const pool = new pg.Pool(config);

pool.on('error', function (err, client) {
  // if an error is encountered by a client while it sits idle in the pool
  // the pool itself will emit an error event with both the error and
  // the client which emitted the original error
  // this is a rare occurrence but can happen if there is a network partition
  // between your application and the database, the database restarts, etc.
  // and so you might want to handle it and at least log it out
  console.error('idle client error', err.message, err.stack);
});

//export the query method for passing queries to the pool
module.exports.query = function (text, values, callback) {
  console.log('query:', text, values);
  return pool.query(text, values, callback);
};

// the pool also supports checking out a client for
// multiple operations, such as a transaction
module.exports.connect = function (callback) {