MongoDB connections keep increasing

Question

I keep hitting my connection limit, but http traffic has remained consistent. I used MMS to profile my mongod process and saw that the number of connections keeps rising:

I'm using the mongoskin wrapper for Node.js (Express). I have a piece of custom route middleware that connects to the mongo db before executing other routes:

var _connect = function(req, res, next) {
  res.db = mongoskin.db(_us.sprintf(
    '%s:%s@localhost:27017/%s?auto_reconnect',
    app.set('mongoDbUser'),
    app.set('mongoDbPw'),
    app.set('mongoDb')
  ));
  next();
};

Am I doing something wrong? How should I be opening and closing connections?

Answer 1

mongoskin is a wrapper for the node-mongodb-native driver so options for the underlying native driver still apply.

Some suggestions to reduce the number of connections used:

1. Open your connection before starting the application (you don't want to open a connection in each request):

    var db = new mongoskin.db(...) 
    db.open(function(err, db) { 
        // Application logic
    })
   

2. Adjust the node-mongo-native connection poolSize. Connection pooling allows a set of connections to be shared in your application rather than always opening new connections. The default poolSize is 1 in older drivers and 5 as of the node-mongo-native 1.1.4 driver which was released Aug 16, 2012.

   So you could try something like:

    var mongoskin = require('mongoskin');
    var serverOptions = {
        'auto_reconnect': true,
        'poolSize': 5
    };
    var db = mongoskin.db('localhost:27017/test', serverOptions);