EMFILE error when using nodejs redis

I want to test how many connections my redis server can hold, so I call redis.createClient() in a loop, while the redis server still runs lively, I got the EMFILE error, I know that I have used out my fds.

but wait, I have just test my mqtt server before, I did the same thing to my mqtt server, I called mqtt.createClient() in a loop of 10000, of 20000... but I never got the EMFILE error .

so, does the nodejs mqtt library use a different mechanism underneath?

redis-client.js :

var redis = require('redis');

function start() {
    var client = redis.createClient();

    client.on('error', function(err) {
        console.log('Error ' + err);
    });
}

exports.start = start;

redis-test.js

var redis_client = require('./redis-client');

for(var i = 0 ; i < 10000 ; ++i) {
    redis_client.start();
    console.log('redis client ' + i + ' started');
}

mqtt-subclient.js

var mqtt = require('mqtt');
function start() {
    var client = mqtt.createClient();
    client.subscribe('message');

    //client.publish('message', 'hello me!');
    client.on('message', function(topic, message) {
        console.log('receive message: ');
        console.log(message);
    });

    client.on('connack', function(packet) {
        console.log(packet);
        if(packet.returnCode == 0) {
            console.log('connect successfully');
        }
    });

    client.on('suback', function(packet) {
        console.log(packet.messageId);
    });

    client.on('error', function(err) {
        console.log(err);
    });
}

exports.start = start;

mqtt-test.js

var subclient = require('./mqtt-subclient.js');

for(var i = 0 ; i < 10000 ; ++i) {
    subclient.start();
    console.log('client ' + i + ' started');
}