NodeJS: Heroku ClearDB not closing connections

Question

I deployed a NodeJS API on Heroku and tried to connect it to a MySQL DB, so I created a connectionPool for handling connections on a ClearDB ignite account (free), which allows a maximum of 10 connections.

Every time I execute a query to the database it just adds a new connection to the stack until it reaches 10 connections and the app crashes.

My code is as follows:

connectionFactory:

var mysql = require('mysql');

function createDBConnection() {
    var conn = mysql.createPool({
      host: 'xxx',
      user: 'xxx',
      password: 'xxx',
      database: 'xxx'
    });
    return conn;
}

module.exports = function() {
  return createDBConnection;
}

And here's my select query:

function Dao(connection) {
  this._connection = connection;
}

Dao.prototype.findAll = function (callback) {
  this._connection.query('SELECT * FROM table',
  function(errors, results) {
    callback(errors,results);
  });
};

module.exports = function() {
  return Dao;
}

Finally here's the route I use to call it:

app.get('/products', function (req,res) {
    var connection = app.persistence.connectionFactory();
    var dao = new app.persistence.Dao(connection);

    dao.findAll(function (err, result) {
      res.format({
        json: function () {
          res.json(result);
        }
      });
    });
  });

I tried changing createPool() to createConnection() and then calling .end()/.destroy() function right after each query but it doesn't work at all.

Any hints?

Answer 1

In order to close a connection / return a connection to the pool use : connection.release()

var mysql = require('mysql');
var pool  = mysql.createPool(...);

pool.getConnection(function(err, connection) {
  // Use the connection
  connection.query('SELECT something FROM sometable', function (error, results, fields) {
    // And done with the connection.
    connection.release();

    // Handle error after the release.
    if (error) throw error;

    // Don't use the connection here, it has been returned to the pool.
  });
});

mysql : Pooling connections Documentation