How to handle a full pool of mysql connections in nodejs - mysql

Question

In my Node script I use MySQL and to be able to handle multiple connections I use a connection pool.
Today I forgot to release a connection in the mysql pool. It took me a long time to figure out what the problem was because there was no error shown anywhere.
My code:
const mysql = require('mysql');
const pool = mysql.createPool({
host : 'x',
user : 'x',
password : '#x',
database : 'x',
connectionLimit: 2
});
function executeQuery(){
pool.getConnection((err, connection) => {
if(err) console.log(err);
let query = mysql.format("SELECT * FROM users WHERE id = ?", 1);
connection.query(query, (err, rows) => {
if(err) console.log(err);
console.log(rows);
});
});
}
executeQuery(); // outputs the user as expected
executeQuery(); // outputs the user as expected
executeQuery(); // there is no output in the console, it just looks like nothing happened
My question: How to find out if there are still connections available and if there are no connection available anymore show an error or handle it in a different way?

Answer 1

You forgot to release your connection:
function executeQuery(){
pool.getConnection((err, connection) => {
if(err) console.log(err);
connection.query("SELECT * FROM users WHERE id = ?", [ 1 ], (err, rows) => {
connection.release(); // Give it back or else it gets lost
if(err) console.log(err);
console.log(rows);
});
});
}
There's also no reason to grab the connection like that, you can just use the pool:
function executeQuery() {
pool.query("SELECT * FROM users WHERE id = ?", [ 1 ], (err, connection) => {
if(err) console.log(err);
console.log(rows);
});
}