NodeJS mysql2 connection in separate file stops soon

Question

connection.js

let mysql = require('mysql2'); let pool = mysql.createPool({ host:'localhost', user: 'root', database: '', password: '', connectionTimeout: 10000 }).promise() pool.getConnection(function(err, connection) { console.log('connected to database') }); pool.on('error', function(err) { console.log(err.code); }); module.exports = { getConnection: () => { return pool.getConnection() } };

other_file.js

router.get('/', async (req, res) => { const conn = await connWrapper.getConnection(); let [courses] = await conn.execute('SELECT * FROM courses'); courses = courses; //database stuff here and page rendering etc });

If I load the page for the first time, it works, however after just a few seconds it stops working and the page won't load anymore, that even if I remove connectionTimeout. Also, how come that I do not receive logs from pool.getConnection and pool.on('error'). There aren't logs in the console whatsoever.

Andrey Sidorov · Accepted Answer · 2020-07-29 07:04:51Z

you need to release connection back to the pool after you no longer need it. Default pool config id connectionLimit: 10, queueLimit: 0, so your first 10 requests use all available connections in the pool and later requests are stuck at await connWrapper.getConnection(); line waiting for previous connections to be available.

Example returning connections to the pool:

router.get('/', async (req, res) => { const conn = await connWrapper.getConnection(); try { const [courses] = await conn.execute('SELECT * FROM courses'); //... } finally { conn.release(); // no need to await here, .release() is sync call } });

Or you can just use .execute() helper on a pool:

// add this to connection.js: // execute: (...args) => pool.execute(...args) router.get('/', async (req, res) => { const [courses] = await connWrapper.execute('SELECT * FROM courses'); // ... });

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