Cannot enqueue Handshake after invoking quit


Question

Here I am doing, propably some basic mistake, In general, I've implemented such a code:

module.exports = {
    getDataFromUserGps: function(callback)
    {
        connection.connect();
        connection.query("SELECT * FROM usergps", 
            function(err, results, fields) {
                if (err) return callback(err, null);
                return callback(null, results);
            }
        ); 
        connection.end();
    },
    loginUser: function(login, pass, callback)
    {
        connection.connect();
        connection.query(
            "SELECT id FROM users WHERE login = ? AND pass = ?",
            [login, pass],
            function(err, results, fields) 
            {
                if (err) return callback(err, null);
                return callback(null, results);
            }
        ); 
        connection.end();
    },
    getUserDetails: function(userid, callback)
    {
        connection.connect();
        connection.query(
            "SELECT * FROM userProfilDetails LEFT JOIN tags ON userProfilDetails.userId = tags.userId WHERE userProfilDetails.userid = ?",
            [userid],
            function(err, results, fields)
            {
                if (err) return callback(err, null);
                return callback(null, results);
            }
        );
        connection.end();
    },
    addTags: function(userId, tags)
    {
        connection.connect();
        connection.query(
            "INSERT INTO tag (userId, tag) VALUES (?, ?)",
            [userId, tags],
            function(err, results, fields)
            {
                if (err) throw err;
            }
        )
        connection.end();
    }
}

And everything works great, but only by first time, If I want to "use" query by the second time I've receive his error:

Cannot enqueue Handshake after invoking quit

I've tried not to .end() connections but it does not help
Thanks in advance
Radek

1
74
12/30/2012 2:57:29 AM

Accepted Answer

If you using the node-mysql module, just remove the .connect and .end. Just solved the problem myself. Apparently they pushed in unnecessary code in their last iteration that is also bugged. You don't need to connect if you have already ran the createConnection call

218
1/9/2013 9:47:40 PM

According to:

TL;DR You need to establish a new connection by calling the createConnection method after every disconnection.

and

Note: If you're serving web requests, then you shouldn't be ending connections on every request. Just create a connection on server startup and use the connection/client object to query all the time. You can listen on the error event to handle server disconnection and for reconnecting purposes. Full code here.


From:

It says:

Server disconnects

You may lose the connection to a MySQL server due to network problems, the server timing you out, or the server crashing. All of these events are considered fatal errors, and will have the err.code = 'PROTOCOL_CONNECTION_LOST'. See the Error Handling section for more information.

The best way to handle such unexpected disconnects is shown below:

function handleDisconnect(connection) {
  connection.on('error', function(err) {
    if (!err.fatal) {
      return;
    }

    if (err.code !== 'PROTOCOL_CONNECTION_LOST') {
      throw err;
    }

    console.log('Re-connecting lost connection: ' + err.stack);

    connection = mysql.createConnection(connection.config);
    handleDisconnect(connection);
    connection.connect();
  });
}

handleDisconnect(connection);

As you can see in the example above, re-connecting a connection is done by establishing a new connection. Once terminated, an existing connection object cannot be re-connected by design.

With Pool, disconnected connections will be removed from the pool freeing up space for a new connection to be created on the next getConnection call.


I have tweaked the function such that every time a connection is needed, an initializer function adds the handlers automatically:

function initializeConnection(config) {
    function addDisconnectHandler(connection) {
        connection.on("error", function (error) {
            if (error instanceof Error) {
                if (error.code === "PROTOCOL_CONNECTION_LOST") {
                    console.error(error.stack);
                    console.log("Lost connection. Reconnecting...");

                    initializeConnection(connection.config);
                } else if (error.fatal) {
                    throw error;
                }
            }
        });
    }

    var connection = mysql.createConnection(config);

    // Add handlers.
    addDisconnectHandler(connection);

    connection.connect();
    return connection;
}

Initializing a connection:

var connection = initializeConnection({
    host: "localhost",
    user: "user",
    password: "password"
});

Minor suggestion: This may not apply to everyone but I did run into a minor issue relating to scope. If the OP feels this edit was unnecessary then he/she can choose to remove it. For me, I had to change a line in initializeConnection, which was var connection = mysql.createConnection(config); to simply just

connection = mysql.createConnection(config);

The reason being that if connection is a global variable in your program, then the issue before was that you were making a new connection variable when handling an error signal. But in my nodejs code, I kept using the same global connection variable to run queries on, so the new connection would be lost in the local scope of the initalizeConnection method. But in the modification, it ensures that the global connection variable is reset This may be relevant if you're experiencing an issue known as

Cannot enqueue Query after fatal error

after trying to perform a query after losing connection and then successfully reconnecting. This may have been a typo by the OP, but I just wanted to clarify.


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