API NodeJS loop or error handling issue: Pool Connections not closing (MYSQL)?

Question

Still playing around with my first ever API NodeJS app.

My current MYSQL Config is:

const mysql = require('mysql');

  var pool = mysql.createPool({    
    host:'localhost',
    user: 'abc',
    password: 'abc',
    database : 'abc',
    multipleStatements: true,
    connectionLimit: 10
});
  
  


module.exports ={
     connection : pool 
} 

My 'order List' section is a way of getting lists of orders outstanding. This page works fine but after clicking a few buttons that bring up lists the program hangs until i restart the API.

Code:

const express = require('express');
const router = express.Router();
const verify = require('../../verifyToken');
var config = require('../../databaseConfig');
var connection= config.connection;

router.get('/getMainPageCount/',verify,(req,res) => {    
    const chemistID = req.user._id;
  
    connection.getConnection(function(error,tmpConn){
        if(error){

        console.log("error in connecting to MYSQL " + error);
        res.sendStatus(500);

        }else{
        
            var sqlString = "SET @chemistID = ?; CALL getMainPageCount(@chemistID);";
            tmpConn.query(sqlString,[chemistID], async (err,rows,fields)=>{
                try{
                    

                    const ListData = rows[1];
                    
                    
                    //console.log(rows); 
                    //console.log(chemistID); 
                    if (rows && Array.isArray(rows) && rows.length) {

                        return res.status(200).json({
                            
                            Result: true,
                        orders: ListData
                        })  

                    }       
                    else
                    {
                        return res.status(500).json({
                            
                            Result: false
                        })
                    }
                } catch (e) {
                    // this catches any exception in this scope or await rejection
                    console.log(e);
                    res.status(500).json({ Result: e });
                }
            })
        }
    })
});

router.get('/getOpenRequests/',verify,(req,res) => {    
    const chemistID = req.user._id;
    var sqlString = "SET @chemistID = ?; CALL getOpenRequests(@chemistID);";

    connection.getConnection(function(error,tmpConn){
        if(error){

            console.log("error in connecting to MYSQL " + error);
            res.sendStatus(500);

        }else{
            try{
                tmpConn.query(sqlString,[chemistID], async (err,rows,fields)=>{
                    const ListData = rows[1];
                    const foundRows = rows[2][0].rowCount;
                    
                    ////console.log(rows[1][0].FirstName); 
                    //console.log(chemistID); 
                    if (rows && Array.isArray(rows) && rows.length) {

                        return res.status(200).json({
                            
                            Result: true,
                        orders: ListData,
                        rowCount: foundRows})  

                    }       
                    else
                    {
                        return res.status(500).json({
                            
                            Result: false
                        })
                        
                    }
                })
            } catch (e) {
                // this catches any exception in this scope or await rejection
                console.log(e);
                res.status(500).json({ Result: e });
            }
        }
    })
    
    
});

router.get('/getOpenOrders/',verify,(req,res) => {    
    const chemistID = req.user._id;
  var sqlString = "SET @chemistID = ?; CALL getOpenOrders(@chemistID);";

    connection.getConnection(function(error,tmpConn){
        if(error){

            console.log("error in connecting to MYSQL " + error);
            res.sendStatus(500);

        }else{
            try{
                tmpConn.query(sqlString,[chemistID], async (err,rows,fields)=>{
                    const ListData = rows[1];
                    const foundRows = rows[2][0].rowCount;
            
                    //console.log(rows[1][0].FirstName); 
                    
                    if (rows && Array.isArray(rows) && rows.length) {

                        return res.status(200).json({
                            
                            Result: true,
                        orders: ListData,
                        rowCount: foundRows})  

                    }       
                    else
                    {
                        return res.status(500).json({
                            
                            Result: false
                        })
                         
                    }
                })
            } catch (e) {
                // this catches any exception in this scope or await rejection
                console.log(e);
                res.status(500).json({ Result: e });
            }
        }
    })
});

router.get('/getOpenFinalised/',verify,(req,res) => {    
    const chemistID = req.user._id;
    var sqlString = "SET @chemistID = ?; CALL getOpenFinalised(@chemistID);";

    connection.getConnection(function(error,tmpConn){
        if(error){

            console.log("error in connecting to MYSQL " + error);
            res.sendStatus(500);

        }else{
            try{
                tmpConn.query(sqlString,[chemistID], async (err,rows,fields)=>{
                    const ListData = rows[1];
                    const foundRows = rows[2][0].rowCount;
            
                    //console.log(rows[1][0].FirstName); 
                    //console.log(chemistID); 
                    if (rows && Array.isArray(rows) && rows.length) {

                            return res.status(200).json({
                                
                                Result: true,
                                orders: ListData,
                                rowCount: foundRows
                            })  

                    }       
                    else
                    {
                        return res.status(500).json({
                            
                            Result: false
                        })  
                    }
                })
            } catch (e) {
                // this catches any exception in this scope or await rejection
                console.log(e);
                res.status(500).json({ Result: e });
            }
        }
    })
});

router.get('/getOpenOverdue/',verify,(req,res) => {    
    const chemistID = req.user._id;
    var sqlString = "SET @chemistID = ?; CALL getOpenOverdue(@chemistID);";

    connection.getConnection(function(error,tmpConn){
        if(error){

            console.log("error in connecting to MYSQL " + error);
            res.sendStatus(500);

        }else{
            try{
                tmpConn.query(sqlString,[chemistID], async (err,rows,fields)=>{
                    const ListData = rows[1];
                    const foundRows = rows[2][0].rowCount;
                    
                    //console.log(rows[1][0].FirstName); 
                    //console.log(chemistID); 
                    if (rows && Array.isArray(rows) && rows.length) {

                        return res.status(200).json({
                            
                            Result: true,
                        orders: ListData,
                        rowCount: foundRows})  

                    }       
                    else
                    {
                        return res.status(500).json({                        
                        Result: false
                        })
                    }
                })
            } catch (e) {
                // this catches any exception in this scope or await rejection
                console.log(e);
                res.status(500).json({ Result: e });
            }
        }
    })
});

This issue was not occuring until I started using this Pool connection plus the error handling.

Now I'm very new to NodeJS (and coding in general) but if i run this on the terminal:

lsof -i tcp:3000

Then i can see everything that is running on that port. When I used ot do this (pre-connection pool) I would just get the node: PID of my Listen.

Now, for about 10 seconds after running any API endpoint I get this:

COMMAND   PID   USER   FD   TYPE    DEVICE SIZE/OFF NODE NAME
node    18993 myserver 18u  IPv6 198273222      0t0  TCP *:hbci (LISTEN)
node    18993 myserver 19u  IPv6 198273223      0t0  TCP vps.myserver.com.au:hbci->myIPAddress:59264 (ESTABLISHED)

Now I assume this is the connection still sitting there... so the connection is not being closed? Could this be the issue? I just don't understand what is wrong with my error handling that I get this hang instead of a crash or something

I had to change to pool connection as it was getting lost connections here and there and after reading about it apparently the pool is the best way to go but I must be missing something? Do I need to release the connection?

Answer 1

You are using the .getConnection method to get a connection instance from the pool of connections. Once you are done with the connection instance you need to close the connection using connection.release();

If this is not done then this connection is not freed and basically, new requests will not have any connection to use

Alternatively, you may use the pool.query method to auto-close the connection after use.

You may check this answer for more details. https://stackoverflow.com/a/57121491/13142033