Pooling keeps incrementing connections and ends up in ER_CON_COUNT_ERROR

Question

I have a class called Connection like one below. This only executes select statements. I have non pooling connection for insert or update.

var _mysql = require('mysql');

function Connection()
{
    //private variables and dependencies includes

    //create mysql pool connection requires nodejs mysql this connection is used only for selects.
    var _connectionSelect = _mysql.createPool({
        host                : _config.mySQLDB.select.dbHost,
        user                : _config.mySQLDB.select.dbUser,
        password            : _config.mySQLDB.select.dbPass,
        database            : _config.mySQLDB.select.dbName,
        supportBigNumbers   : true,
        connectTimeout      : 7000,
        connectionLimit     : 5,
        queueLimit          : 5
    });
this.executeSelect = function(sql, callback, Message)
    {
        //connects to mysql.
        _connectionSelect.getConnection(function(connectionError, Connection){
            if(connectionError)
            {
                console.log(connectionError);
                //throws error if connection or sql gone wrong
                Message.add("error", 'serviceDown');
                Message.add("devError", 'unknownError');
                callback(false);
            }
            else
            {
                //executes the query passed
                Connection.query(sql, function(error, rows) {
                    Message.incerementQuery();
                    if(error)
                    {
                        Connection.release();
                        console.log(error+sql);
                        //throws error if connection or sql gone wrong
                        Message.add("error", 'unknownError');
                        Message.add("devError", "seriousError", "Database errors at resource server side");
                        callback(false);
                    }
                    else
                    {
                        Connection.release();
                        //executes the callback function
                        callback(rows);
                    }
                });
            }
        });
    };
}

exports.Connection = Connection;

I created an instance of this class whenever I want to execute a query.

I am aware that the default concurrent connections in MySQL is 100 and I wanted to keep that number.

Whenever I try running my application, this connection pooling is incrementing every select and reaches 100 connections pretty soon.

As you can see I am releasing the connection on success or error states. I am pretty sure that I must be doing something wrong, but difficult to figure out.

Is it because how I create instances of this class? I was hoping that if I supply

connectionLimit : 5

even if I create many instances of this class it should only utilise 5 connection?

Note: I have only one instance of this app in my local machine.

Sorry to be so amateur, I am new to this streaming I/O business. I love the idea of pooling but if I cant sort this out, I may need to use traditional open and close connection for every query . Any help would be much appreciated.

Many thanks,

Karthik

Answer 1

Got the answer from Doug Wilson from git hub https://github.com/dougwilson.

I should have instantiated createPool outside of the function. Works like a charm.

The code goes like

    var _mysql = require('mysql');
//create mysql pool connection requires nodejs mysql this connection is used only for selects.
        var _connectionSelect = _mysql.createPool({
            host                : _config.mySQLDB.select.dbHost,
            user                : _config.mySQLDB.select.dbUser,
            password            : _config.mySQLDB.select.dbPass,
            database            : _config.mySQLDB.select.dbName,
            supportBigNumbers   : true,
            connectTimeout      : 7000,
            connectionLimit     : 5,
            queueLimit          : 5
        }


    function Connection()
    {
        //private variables and dependencies includes

       );
    this.executeSelect = function(sql, callback, Message)
        {
            //connects to mysql.
            _connectionSelect.getConnection(function(connectionError, Connection){
                if(connectionError)
                {
                    console.log(connectionError);
                    //throws error if connection or sql gone wrong
                    Message.add("error", 'serviceDown');
                    Message.add("devError", 'unknownError');
                    callback(false);
                }
                else
                {
                    //executes the query passed
                    Connection.query(sql, function(error, rows) {
                        Message.incerementQuery();
                        if(error)
                        {
                            Connection.release();
                            console.log(error+sql);
                            //throws error if connection or sql gone wrong
                            Message.add("error", 'unknownError');
                            Message.add("devError", "seriousError", "Database errors at resource server side");
                            callback(false);
                        }
                        else
                        {
                            Connection.release();
                            //executes the callback function
                            callback(rows);
                        }
                    });
                }
            });
        };
    }

    exports.Connection = Connection;

Thanks a lot. Sorry to be so stupid.

Karthik