When database is changed value is not updating in socket.io - mysql

Question

I have write code of socket.io and nodejs to fetch value from database and send the value to the client without refresh with setInterval. It is working fine but I don't want to use setInterval function. Because sometimes my database change in hours, sometimes in minuts and sometimes in miliseconds. So I don't want to use setInterval function. I only want that when database value change it automatically update. thats it. I am kinda stuck in it.
var express = require('express');
var app = express();
var server = require('http').createServer(app);
var io = require('socket.io').listen(server);
var mysql = require('mysql');
users = [];
connections = [];
disconnection = [];
var connection = mysql.createConnection({
host: 'localhost',
user: 'root',
password: '',
database: 'test'
});
connection.connect(function(error){
if(!!error) {
console.log('Error in connection');
} else {
console.log('Database Connected');
}
});
server.listen(process.env.PORT || 3000);
console.log('Server Running...');
app.get('/', function(req, res) {
res.sendFile(__dirname + '/index.html');
});
io.sockets.on('connection', function(socket) {
connections.push(socket);
console.log('Connected: %s socket connected',
connections.length);
setInterval(function() {
connection.query('select value from piechart',
function(error, rows, fields) {
if(rows.length>0) {
io.sockets.emit('new message', {msg: rows});
//io.sockets.emit('new message', {msg:
'Change.'});
//console.log('Value is fetched from database');
//console.log(rows);
} else {
alert('what will happend');
}
//connection.release();
});
}, 3000);
});

Answer 1

You should take the interval out of the socket scope and make it global.
Then make an interval loop that fetches the value and emits it globally if the value changed from last time it was fetched, to all connected socket clients.
You state that you would like to avoid an interval, but at the end you are going to be needing one.
You can check out mysql-events
A Node JS NPM package that watches a MySQL database and runs callbacks
on matched events.
Another way around it, would be to find all the events that update the value and make them inform your NodeJS process.
But this might be hard if it has components that are out of your control (example : unable of adding code to other process that updates DB)