sequelize-pool

What is sequelize-pool?

The sequelize-pool npm package is a standalone library for managing resource pools, such as database connections. It is designed to be used with Sequelize, a popular ORM for Node.js, but can also be used independently. The package provides a robust and efficient way to manage and reuse resources, ensuring optimal performance and resource utilization.

What are sequelize-pool's main functionalities?

Creating a Pool

This code demonstrates how to create a new resource pool using sequelize-pool. The pool is configured with a name, create and destroy functions for managing resources, and parameters for maximum and minimum resources, as well as idle timeout.

const Pool = require('sequelize-pool').Pool;
const pool = new Pool({
  name: 'my-pool',
  create: function() {
    return new Promise((resolve) => {
      resolve({}); // Simulate resource creation
    });
  },
  destroy: function(resource) {
    return new Promise((resolve) => {
      resolve(); // Simulate resource destruction
    });
  },
  max: 10,
  min: 2,
  idle: 10000
});

Acquiring a Resource

This code demonstrates how to acquire a resource from the pool. Once the resource is acquired, it can be used for various operations. After usage, the resource is released back to the pool.

pool.acquire().then((resource) => {
  console.log('Resource acquired:', resource);
  // Use the resource
  pool.release(resource);
});

Releasing a Resource

This code demonstrates how to release a resource back to the pool after it has been used. Releasing resources ensures they can be reused, optimizing resource management.

pool.acquire().then((resource) => {
  console.log('Resource acquired:', resource);
  // Use the resource
  pool.release(resource).then(() => {
    console.log('Resource released');
  });
});

Draining the Pool

This code demonstrates how to drain the pool, which means no new resources will be created. After draining, all existing resources are destroyed. This is useful for gracefully shutting down applications.

pool.drain().then(() => {
  console.log('Pool drained');
  return pool.destroyAllNow();
}).then(() => {
  console.log('All resources destroyed');
});

Other packages similar to sequelize-pool

generic-pool

generic-pool is a generic resource pool library for Node.js. It provides similar functionality to sequelize-pool, including resource creation, acquisition, release, and destruction. However, generic-pool is more general-purpose and can be used for a wider range of resource types.

README

sequelize-pool

Resource pool. Can be used to reuse or throttle expensive resources such as database connections.

This is a fork from generic-pool@v2.5.

Installation

$ npm install --save sequelize-pool
$ yarn add sequelize-pool

Example

Step 1 - Create pool using a factory object

// Create a MySQL connection pool
var Pool = require('sequelize-pool').Pool;
var mysql2 = require('mysql2/promise');

var pool = new Pool({
    name     : 'mysql',
    create   : function() {
      // return Promise
      return mysql2.createConnection({
        user: 'scott',
        password: 'tiger',
        database:'mydb'
      });
    },
    destroy  : function(client) { client.end(); },
    max      : 10,
    // optional. if you set this, make sure to drain() (see step 3)
    min      : 2,
    // Delay in milliseconds after which available resources in the pool will be destroyed.
    idleTimeoutMillis : 30000,
    // Delay in milliseconds after which pending acquire request in the pool will be rejected.
    acquireTimeoutMillis: 30000,
     // Function, defaults to console.log
    log : true
});

Step 2 - Use pool in your code to acquire/release resources

// acquire connection
pool.acquire().then(connection => {
  client.query("select * from foo", [], function() {
  // return object back to pool
    pool.release(client);
  });
});

Step 3 - Drain pool during shutdown (optional)

If you are shutting down a long-lived process, you may notice that node fails to exit for 30 seconds or so. This is a side effect of the idleTimeoutMillis behaviour -- the pool has a setTimeout() call registered that is in the event loop queue, so node won't terminate until all resources have timed out, and the pool stops trying to manage them.

This behaviour will be more problematic when you set factory.min > 0, as the pool will never become empty, and the setTimeout calls will never end.

In these cases, use the pool.drain() function. This sets the pool into a "draining" state which will gracefully wait until all idle resources have timed out. For example, you can call:

// Only call this once in your application -- at the point you want
// to shutdown and stop using this pool.
pool.drain().then(() => pool.destroyAllNow());

If you do this, your node process will exit gracefully.

Draining

If you know would like to terminate all the resources in your pool before their timeouts have been reached, you can use destroyAllNow() in conjunction with drain():

pool.drain().then(() => pool.destroyAllNow());

One side-effect of calling drain() is that subsequent calls to acquire() will throw an Error.

Pool info

The following functions will let you get information about the pool:

// returns factory.name for this pool
pool.name

// returns number of resources in the pool regardless of
// whether they are free or in use
pool.size

// returns number of unused resources in the pool
pool.available

// returns number of callers waiting to acquire a resource
pool.waiting

// returns number of maxixmum number of resources allowed by ppol
pool.maxSize

// returns number of minimum number of resources allowed by ppol
pool.minSize

Run Tests

$ npm install
$ npm test