For testing purposes, I've set up this little script:

Client = require('mysql').Client, client = new Client(); 
client.user = 'root'; client.password = 'root'; client.port = 8889;

counter = 0; data = '';
setInterval(update, 10);

function update(){
    counter++; request();
}
var sys = require('sys'), fs = require('fs'), http = require('http'),
    url = require('url'),port = 8001;

http.createServer(function(request, response) {
    response.writeHead(200, {
        'Content-Type': 'text/html'
    }); response.end('Hello world');
}).listen(port);

function request(){
    client.connect();
    client.query('USE db');
    client.query(
    'SELECT * FROM table', function selectCb(err, results, fields) {
        if (err) { throw err; }
        if(results.length > 0)
        {
            var firstResult = results[0];
            data = firstResult['data'];
        }
        client.end();
    }
    );
}

It works fine, but, after an hour or so, the server crashes and outputs the following error:

node.js:180
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: EADDRINUSE, Address already in use

UPDATE

I updated the code. It now includes some mysql. This definitely is causing the problem, although I don't know exactly why. Leaving this part out stabilizes the loop. Also, I updated the time interval to every 10 ms. (The server crashes after a few minutes with the mysql part in it, but keeps on running without)

For testing purposes, I've set up this little script:

Client = require('mysql').Client, client = new Client(); 
client.user = 'root'; client.password = 'root'; client.port = 8889;

counter = 0; data = '';
setInterval(update, 10);

function update(){
    counter++; request();
}
var sys = require('sys'), fs = require('fs'), http = require('http'),
    url = require('url'),port = 8001;

http.createServer(function(request, response) {
    response.writeHead(200, {
        'Content-Type': 'text/html'
    }); response.end('Hello world');
}).listen(port);

function request(){
    client.connect();
    client.query('USE db');
    client.query(
    'SELECT * FROM table', function selectCb(err, results, fields) {
        if (err) { throw err; }
        if(results.length > 0)
        {
            var firstResult = results[0];
            data = firstResult['data'];
        }
        client.end();
    }
    );
}

It works fine, but, after an hour or so, the server crashes and outputs the following error:

node.js:180
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: EADDRINUSE, Address already in use

UPDATE

I updated the code. It now includes some mysql. This definitely is causing the problem, although I don't know exactly why. Leaving this part out stabilizes the loop. Also, I updated the time interval to every 10 ms. (The server crashes after a few minutes with the mysql part in it, but keeps on running without)

• javascript
• node.js

• What about listening on another port? – pimvdb Commented Jul 20, 2011 at 8:52
• @pimvdb - Would that make a difference? – Kriem Commented Jul 20, 2011 at 8:53
• Personally, I've used random ports like 15382 without that error so far, so it might be worth a try. – pimvdb Commented Jul 20, 2011 at 8:54
• I'm trying it as we speak, but out of curiosity, how would that make a difference? – Kriem Commented Jul 20, 2011 at 9:09
• 2 Perhaps you'd want to try connecting once and execute a query each 10ms without disconnecting. Connecting 100 times a second doesn't sound like a good idea. – pimvdb Commented Jul 20, 2011 at 12:18

2 Answers 2

You really should honor pimvb's ment about not connecting 100 times a second to the database. If node-mysql doesn't clean up the connections correctly or immediately this will most likely have you run out of available ports for connections within about an hour (actually more like 10 minutes or so, use netstat | grep WAIT | wc -l to see how many closed connections you have pending).

Also, you should be aware of the asynchronous nature of JavaScript/node.js. You might not want to run new queries in such a tight loop while other queries are still pending. This will only pile up and the SQL server will choke.

UPDATE

Something like the following should prevent you from choking your server. It will issue as many request as possible but no more than 1 every 10 ms. Disclaimer: hacked in so textbox, not tested!

Client = require('mysql').Client, client = new Client(); 
client.user = 'root'; client.password = 'root'; client.port = 8889;

counter = 0; data = '';

client.connect(function {
    setInterval(update, 10);

    var queryPending = false, queryReIssue = false;

    function update(){
        if (queryPending) {
            queryReIssue = true;
        } else {
            request();
        }
        counter++;
    }
    var sys = require('sys'), fs = require('fs'), http = require('http'),
        url = require('url'),port = 8001;

    http.createServer(function(request, response) {
        response.writeHead(200, {
            'Content-Type': 'text/html'
        }); response.end('Hello world');
    }).listen(port);

    function request(){
        requestPending = true;
        client.query('USE db');
        client.query('SELECT * FROM table', function selectCb(err, results, fields) {
            requestPending = false;
            if (err) { console.log('ERROR: ' + err.message) }
            if(results.length > 0) {
                var firstResult = results[0];
                data = firstResult['data'];
            }
            if (queryReIssue) {
                queryReIssue = false;
                request();
            }
        });
    }
});

You are connecting every 10ms, which puts a heavy load on your MySQL server. I do not know how it's possible that you get a 'address in use' error, but you might want to try connecting once and use the connection to execute queries.

Just like you don't log out and log back in again and again at a messenger application for each message you want to send to someone :)