I've got a simple express server running on NodeJS and I wish to perform database queries when receiving demands. My setup looks such as this

var srv = require('express').createServer();
var db = new DbConnection(dsn);

srv.get('/', function (req, res) {
    var result = db.query(query);

    res.send(result);
});

srv.listen(80);

Am I Going To experience concurrency ? Let's say two demands are now being handled concurrently and therefore the querying is performed concurrently ?

I additionally considered this method

srv.get('/', function (req, res) {
    var db = new DbConnection(dsn);

    var result = db.query(query);

    res.send(result);
});

Exactly what do you factor is the greatest approach/practice to get this done ?

The important thing to node.js performance would be to never block the thread.

var result = db.query(query);

is really a large no no.

db.query(query, function(result) {
  res.send(result);
});

may be the way queries for demands ought to be handled

hooking up once ought to be fine, most databases don't have any difficulties with queues.