I have used one signle connection object of MYSQL in node JS to serve for multiple users.
I mean to say that MySQL connection will be created upon starting the script & it will remain same until the life of the node script/server.
Practically, this is possible to do & i have done the same. Please take a look at below code of NodeJS/MySQL script.
#################################
var http = require('http');
var mysql = require('mysql');
var con = mysql.createConnection({
host: "192.168.1.105",
user: "root",
password: "XXXXXX",
database: "mydb"
});
con.connect(function(err) {
if (err) {
console.error('error: ' + err.message);
process.exit(1);
}
http.createServer(function (req, res) {
continueExecution(req,res);
}).listen(8082);
});
async function continueExecution(req,res){
res.write('calledddd\n');
for (let step = 0; step < 50; step++) {
// Runs 5 times, with values of step 0 through 4.
var bar = `Company Inc ${step}`;
var sql = `INSERT INTO customers (name, address) VALUES ('${bar}', 'Highway 37')`;
res.write(sql + "\n");
con.query(sql, function (err, result) {
if (err) throw err;
res.write("1 record inserted\n");
});
}
res.write('reached\n');
for (let ste = 0; ste < 50; ste++) {
res.write('started Update\n');
var bar = `Company Inc ${ste}`;
var sql = `UPDATE customers SET name = 'UPDATE RECORD' WHERE name = '${bar}'`;
con.query(sql, function (err, result) {
if (err) throw err;
res.write(result.affectedRows + " record(s) updated\n");
if(ste == 50) {
res.writeHead(200, {'Content-Type': 'text/html\n'});
res.write('Databse connected\n');
res.end();
}
});
}
}
#################################
I have several questions in my mind as i am technical expert. But i didn't find any resources over my questions. Please help me on this
Q1. Are there any type of consequences of using one single MySQL connection to provide response to multiple users?
Q2. Let's take an example.
100 users wants to access table name "users_data" at the same time. 25 users are updating their records on the same table with unique primary key. 50 users are selecting their records. another 25 users deleting their records.
All these operations are being done at the same time via parallel Node Script calls from remote device.
To complete all these MySQL transactions, system is using only 1 database connection.
What will happen in this case?
To answer your questions, one of the consequences of using a unique connection is that it can lead to slower request execution.
In fact, even if node will make the requests asynchronously, your database will execute all those requests synchronously, so one after the other in the order they came. As node makes the requests asynchronously, the order in which they are executed by your database is not granted, and the issue you are referencing to might happen.
One easy way to avoid this is to use a connection pool which will create a given number of connection, using the same db user. Here are some links that might help you with this :
using a connection pool with node.js
connect a mysql database with node.js
Related
I'm trying to get the smallest ID (by world) that is not used via this SQL query:
"SELECT MAX(`objects`.`id`) as nextID FROM `objects` WHERE `objects`.`world`='1'"
NodeJS:
var mysql = require('mysql');
var pool = mysql.createPool({
connectionLimit: 10,
host: '********',
user: '*********',
password: '*******',
database: databaseName
});
function getNextObjectID(worldID, cb) {
var q = "SELECT MAX(`objects`.`id`) as nextID FROM `objects` WHERE `objects`.`world`='"+worldID+"'";
console.log(q);
pool.query(q, function(err, results, fields) {
console.log(err);
console.log(results);
console.log(fields);
});
}
Previously, I had a more in depth approach that included ids used previously, but it also was having this issue so I've reverted down to this simpler method.
I run this through node and phpmyadmin. When node is doing it, it automatically inserts the world id (and yes I print out the actual query and get that it is identical upon execution). When phpmyadmin executes it returns 14. When node executes its rarely 14 and most of the time null. I have no idea why it would change. All other queries behave normally.
There was an asynchronous delete being called by someone else, it was reading next id before a large amount of rows got inserted.
I am running a query which gives me confusing results. I have a node.js server which takes some user input from a form on the client side and uses socket.io to get the input on the server. here is the function which runs after receiving user input
databaseCheck(data);
function databaseCheck(userInput){
var mysql = require('mysql');
var connection = mysql.createConnection({
host : '12.34.56.78',
user : 'user',
password : 'password',
database : 'db'
});
connection.connect();
var query = connection.query('SELECT * from `table` WHERE `email` = userInput', function(err, rows, fields) {
if (!err) console.log(rows[0].username);
else console.log("connection failure");
});
connection.end();
}
So when ever I use this code, it keeps printing "connection failure" to the screen. It doesn't happen when I replace userInput with the "example#email.com" so I'm guessing there is some problem with using the variable userInput in the query. Can someone tell me what is wrong with my code?
Not only do you need to pass the userInput by appending it to the string, you need to escape it so that the query recognizes it as a string:
connection.connect();
var query = 'SELECT * from `table` WHERE `email` = ' + JSON.stringify(userInput);
console.log(query);
connection.query(query, function(err, rows, fields) {
if (!err) console.log(rows[0].username);
else console.log(err.name, err.message);
});
connection.end();
It also helps to make the error message more informative by displaying the actual error instead of a generic message.
Lastly, put connection.end(); inside the callback. According to what you said, it appears to work like you had it but it's generally a bad idea to end a connection before an asynchronous process using the connection has called back.
Ignore my last comment, it appears I was wrong in this particular case. According to the repository documentation, it says:
Closing the connection is done using end() which makes sure all remaining queries are executed before sending a quit packet to the mysql server.
Try this for testing and resolution. Printing to the log will let you see what you are putting in the query.
var querystring = "SELECT * from table WHERE email LIKE " +
userInput;
console.log(querystring);
var query = connection.query(querystring, function(err, rows, fields) {...
I am trying to learn node.js so that I can actually get started on working on my personal project. I have been trying to follow the examples in the book "Learning node.js" (by Marc Wandschneider). I, at this point, decided to forgo practicing his example, and go straight into using his code as framework for my practice code.
In my practice code, all I am trying to do is connect to my RDS database (no, I am not using Elastic Beanstalk, btw), and output contents of one of the tables. Seems simple enough, but when I whip up the code for it (based on the book), it seems to attempt connection, but get hung up in the process. This is my code:
var pool = require('generic-pool');
var async = require('async');
var mysql = require('mysql');
var host = "<database-name>.cu8hvhstcity.us-west-2.rds.amazonaws.com",
database = "<database-name>",
user = "<username>",
password = "<someLongPassword>";
var dbClient;
async.waterfall([
// 1. establish connection to database
function (callback) {
console.log("Connecting to database " + database + "...");
dbClient = mysql.createConnection({
host: host,
database: database,
user: user,
password: password,
port: 3306
});
dbClient.connect();
},
// 2. select all from a table (let's go for locations)
function (cb)
{
var query = "SELECT * FROM locations"
console.log("running query \"" + query + "\"...");
dbClient.query(query, cb);
},
function (rows, fields, callback)
{
console.log(fields);
for (var i = 0; i < rows.length; i++)
{
console.log(JSON.stringify(rows, null, '\t'));
}
}
], function (err, results) {
if (err)
{
console.log("An error occurred...");
console.log(err);
}
else
{
console.log("Everything successfully completed!");
}
dbClient.end();
})
This is better than first attempt, when I put a database member to the argument passed to mysql.createConnection(), and it complained that database was unknown. In neither case did either "An error occurred..." nor "Everything successfully completed!" output to the window.
Is there any async stuff going on that is resulting in some kind of non-terminating infinite loop or something? How do I fix this?
The book has an associated GitHub page
NOTE:
Neither my example nor the cited GitHub code make use of that pool variable, so it can simply be commented out. All you need to do to run this yourself is to say npm install async,npm install mysql (as well as creating a dummy RDS database to point to, that contains locations table) before copying, pasting, and running this code.
EDIT:
I fixed the issue with database. I realized that the name of the database used '_', not '-'. Same issue (code hangs) still persists...
I did the following:
In the second function in the array, I needed two parameters, not one.
I fixed thus:function(results, cb)
The third function simply needed to callback(null)
The situation is: In one http GET request I need to select from one table the information I need and send to the client, and at the same time I need to retrieve the user IP and insert into a database. I'm using Node.js for this experiment.
The thing is: Is there a way to make the two actions together? Or do I have to connect and make two separate queries? Is there a way to render the page and do the other INSERT action in the background? What is the fastest option?
app.get('/', function({
connect.query("SELECT column1, column2 FROM table;", function(err, ...
render("index", ...);
});
connect.query("INSERT INTO table2 SET ip=11111111;");
});
The procedure approach suggested by #skv is nice but you have to wait for the write before doing the read and eventually returning a result to the user.
I would argue for another approach.
Queue the ip-address and a timestamp internally in something like an array or list.
Do the read from the database and return a result to the user
Create a background job that will nibble of the internal array and do the inserts
This has several benefits
The user gets a result faster
The writes can be done later if the system is being called in bursts
The writes can be done in batches of tens or hundreds of inserts reducing the time it takes to write one row.
You can make a stored procedure do this
Basically these are two different operations, but doing it in stored procedures might give you the assurance that it will surely happen, you can pass the IP address as the parameter into the stored procedure, this will also avoid any worries of performance in the code for you as the db takes care of insert, please remember that any select that does not insert into a table or a variable will produce a result set for you to use, hope this helps.
DELIMITER $
CREATE PROCEDURE AddIPandReturnInfo
(
#IPAddress varchar(20)
)
BEGIN
INSERT INTO Yourtable (IPAddress);
SELECT * FROM Tablename;
END $
DELIMITER ;
Well, I assume you're using this module https://github.com/felixge/node-mysql
The MySQL protocol is sequential, then, to execute paralell queries against mysql, you need multiple connections. You can use a Pool to manage the connections.(builtin in the module)
Example:
var mysql = require('mysql');
var pool = mysql.createPool({
host: 'example.org',
user: 'bob',
password: 'secret',
connectionLimit: 5 // maximum number of connections to create at once **10 by default**
});
app.get('/', function (req, res) {
// get a connection from the pool //async
pool.getConnection(function (err, connection) {
// Use the connection
connection.query('SELECT something FROM table1', function (err, rows) {
// Do somethig whith the mysql_response and end the client_response
res.render("index", {...
});
connection.release();
// Don't use the connection here, it has been closed.
});
});
//async
var userIp = req.connection.remoteAddress || req.headers['x-forwarded-for'] || null;
if (userIp) {
// get a connection from the pool again
pool.getConnection(function (err, connection) {
// Use the connection
connection.query('INSERT INTO table2 SET ip=?', [userIp], function (err, rows) {
// And done with the insert.
connection.release(); // Conn Close.
});
});
}
});
I've begun playing around with Node.js lately, for many reasons but most importantly the ease at which I can write a chat-server utilising HTML5 WebSockets. However, I've been stuck for weeks with MySQL.
I'm currently using this MySQL client module: https://github.com/sidorares/nodejs-mysql-native
I've connected to the database and managed to store data using the following code:
// MySQL database
var db = require("mysql-native").createTCPClient(); // localhost:3306 by default
db.auto_prepare = true;
db.auth(dbName, dbUser, dbPass);
// Update the database
db.execute("UPDATE server_data SET value='" + new Date() + "' WHERE name='lastLoaded'");
How may I go about retrieving data from the database using a SELECT * FROM x WHERE y=z query?
Is there any specific reason you chose nodejs-mysql-native over node-mysql which is a really good node module. If there is none, then you should probably try node-mysql. I've tried it and it is great to start off using MySQL with Node. You could do something like:
var mysql = require('mysql');
var connection = mysql.createConnection({
host : 'localhost',
user : 'your_username',
password : 'your_password',
});
connection.connect();
connection.query("UPDATE server_data SET value=? WHERE name=?", [new Date(), 'lastLoaded'] function(err, result) {
if (err) throw err;
console.log('Result: ', result);
});
connection.end();
The advantage you get by using it this way is that you can prevent SQL injection, which is taken care of internally in node-mysql (by using the connection.escape() method).