mysql million rows express.js slow response - mysql

Question

I am using node.js v0.10.33 with node-mysql 2.5.4 and express.js 4.10.2 and fast-csv 0.6.0
Any following requests made to the server slows down after a request to "query 9000000 rows and download it as csv". Is there a better way to avoid the slow response?
/**
* problem is why the server response slows down on a large request mande to mysqlrows_to_csv which queries 9000000 rows and saves as csv
*/
(function () {
'use strict';
var async = require('async');
var csv = require("fast-csv");
var fs = require('fs');
var mysql = require('mysql');
//var express = require('express');
//var expRouter = express.Router(); // Express Router
expRouter.get('/mysqlrows_to_csv/', function(req, res, next) {
mysqlrows_to_csv(function(err) {
console.log('use socket to emit a notification to client saying csvfile is ready');
});
res.json({'mysqlrows_to_csv': true});
return res.end();
});
expRouter.get('/some_other_queries/', function(req, res, next) {
res.json({'some_other_queries': true});
return res.end();
});
function mysqlrows_to_csv(callback) {
var csvStream;
var connProp = {
host : 'host',
user : 'user',
password : 'password',
database : 'database'
};
var I = 0;
async.waterfall([
function(cb) {
var connection = mysql.createConnection(connProp);
connection.connect(function(err) {
if (err) return callback(err);
csvStream = csv.createWriteStream({headers: true});
var writableStream = fs.createWriteStream("dump_mysql_to_csv.csv");
writableStream.on("error", function(err){
return callback(err);
});
writableStream.on("finish", function(){
console.log("DONE!");
return callback(null);
});
if (csvStream) csvStream.pipe(writableStream);
return cb(err, connection);
});
},
function(connection, cb) {
var qry = 'select * from table'; // this has aleast 9000000 rows
var query = connection.query(qry);
query
.on('error', function(err){
return cb(err);
})
.on('result', function(row) {
connection.pause();
I = I + 1;
console.log('row no.', I);
if (csvStream) csvStream.write(row);
connection.resume();
})
.on('end', function() {
console.log('stream-ended')
if (csvStream) csvStream.end();
return cb(null, connection);
});
},
function(connection, cb) {
connection.end(function(err) {
if (err) {
console.log('Error while disconnecting mysql', err);
}
console.log('The connection is terminated now');
console.log('final conn state:', connection.state);
});
}
]);
}
}());