NodeJS Mysql pool.query() not releasing connections?

Question

I am having trouble with pooling mysql connections with nodeJS. As I understand it, when creating a pool, I should be able to use pool.query() to:

1. Get a connection
2. Run my query
3. Release the connection

However, the issue I am running into is the connections remain open and "sleeps" until the server closes the connection itself (60 seconds). Is there something I am doing wrong here? For context, I am connecting to Heroku clearDB and am viewing the connection on its dashboard.

Example: Upon login, I make a query to check login credentials to authenticate, another query to fetch one set of data, and another query to fetch another set. After logging in, the server is left with 2 connection in "sleep" mode. They do not disconnect until 60 seconds expire.

Here is my db.js file:

const mysql = require("mysql");

const dbConfig = require("./db.config.js");

const connection = mysql.createPool({
    host: dbConfig.HOST,
    user: dbConfig.USER,
    password: dbConfig.PASSWORD,
    database: dbConfig.DB,
    port: dbConfig.PORT,
    multipleStatements: true,
    connectionLimit: 10
})

module.exports = connection;

Here is how I am making queries:

const sql = require("./db.js"); //Our db connection
---OMITTED---
return new Promise((resolve, reject) => {
        const select_user = "SELECT user_id, first_name, last_name, username, password, is_admin, is_active FROM users WHERE username = ? LIMIT 1"
        const params = [username]
        const user_pass = password

        sql.query(select_user, params, (err, res) => {
            if (res) {
                if (res.length) {
                    const user = res[0]
                    const hash = user.password
                    const is_active = user.is_active
                    if (is_active) {
                        bcrypt.compare(user_pass, hash).then(res => {
                            if (res) {
                                resolve({ result: true, info: { fname: user.first_name, lname: user.last_name, username: user.username, is_admin: user.is_admin, user_id: user.user_id } })
                            } else {
                                reject({ result: false, msg: "wrong_creds" })
                            }
                        }).catch(err => {
                            reject({ result: false, msg: err })

                        })
                    } else {
                        reject({ result: false, msg: "inactive" })
                    }


                } else {
                    reject({ result: false, msg: "user_not_exist" })
                }

            } else {
                console.log("MYSQL QUERY, COULD NOT SELECT USER FOR AUTHENTICATION")
                reject({ result: false, msg: err })
            }
        })


})

I'm under the impression that pool.query() will close the connection for me after each query. Is this not the case? Am I missing something once the query has been completed?

I have also tried the manual way:

        const select_string = "SELECT * FROM user_backlogs WHERE movie_id = ? AND user_id = ?"
        const params = [movie_id, user_id]
        sql.getConnection((err, connection) => {
            if (err) reject(err)
            else {
                connection.query(select_string, params, (err, res) => {
                    connection.release()
                    if (err) reject(err)
                    else {
                        if (res.length) {
                            resolve([movie_id, "exists", res[0]["added_on"]])
                        } else {
                            resolve([movie_id, "not_exists"])
                        }
                    }
                })
            }
        })

But still, the connections remain up until the server kicks them off. Any help is greatly appreciated.

Answer 1

The pool will not close the connection. It will release the connection, which me means it can be reused by another query. The pool does this to optimize performance, since it takes time to open a new connection.

If you want to close the connection after use, you can explicitly destroy it ( connection.destroy() ) and the pool will create a new one the next time you issue a query. You can find more information on this in the documentation under pooling connections .