什么时候使用 node-mysql 关闭 MySQL 连接？

Question

Currently using: https://github.com/felixge/node-mysql

I have the following code:

var connection = mysql.createConnection({
    host     : 'localhost',
    user     : 'me',
    password : 'secret',
    database : 'Database1'
});
app.put('/api/upload', function(req, res, next)
{
    connection.connect();
    doMultipleQueries(function(err)
    {
        connection.end();
    });          
};

The put request works perfectly fine, but calling it the second time, I get the following error

events.js:68
        throw arguments[1]; // Unhandled 'error' event
                       ^
Error: Cannot enqueue Handshake after invoking quit.
    at Protocol._validateEnqueue (/Users/anon/Desktop/project Web/node_modules/mysql/lib/protocol/Protocol.js:110:16)

Am I supposed to leave the connection open until the server dies?

UPDATE: When I move the mysql.createConnection into the put request function like so:

var connection = null; 
app.put('/api/upload', function(req, res, next)
{
    connection = mysql.createConnection({
        host     : 'localhost',
        user     : 'me',
        password : 'secret',
        database : 'Database1'
    });
    connection.connect();
    doMultipleQueries(function(err)
    {
        connection.end();
    });          
};

It works fine. Does this mean connection.end() closes what mysql.createConnection created and cannot be reconnected?

Answer 1

Currently using: https://github.com/felixge/node-mysql

I have the following code:

var connection = mysql.createConnection({
    host     : 'localhost',
    user     : 'me',
    password : 'secret',
    database : 'Database1'
});
app.put('/api/upload', function(req, res, next)
{
    connection.connect();
    doMultipleQueries(function(err)
    {
        connection.end();
    });          
};

The put request works perfectly fine, but calling it the second time, I get the following error

events.js:68
        throw arguments[1]; // Unhandled 'error' event
                       ^
Error: Cannot enqueue Handshake after invoking quit.
    at Protocol._validateEnqueue (/Users/anon/Desktop/project Web/node_modules/mysql/lib/protocol/Protocol.js:110:16)

Am I supposed to leave the connection open until the server dies?

UPDATE: When I move the mysql.createConnection into the put request function like so:

var connection = null; 
app.put('/api/upload', function(req, res, next)
{
    connection = mysql.createConnection({
        host     : 'localhost',
        user     : 'me',
        password : 'secret',
        database : 'Database1'
    });
    connection.connect();
    doMultipleQueries(function(err)
    {
        connection.end();
    });          
};

It works fine. Does this mean connection.end() closes what mysql.createConnection created and cannot be reconnected?

Answer 2

Currently using: https://github.com/felixge/node-mysql

I have the following code:

var connection = mysql.createConnection({
    host     : 'localhost',
    user     : 'me',
    password : 'secret',
    database : 'Database1'
});
app.put('/api/upload', function(req, res, next)
{
    connection.connect();
    doMultipleQueries(function(err)
    {
        connection.end();
    });          
};

The put request works perfectly fine, but calling it the second time, I get the following error

events.js:68
        throw arguments[1]; // Unhandled 'error' event
                       ^
Error: Cannot enqueue Handshake after invoking quit.
    at Protocol._validateEnqueue (/Users/anon/Desktop/project Web/node_modules/mysql/lib/protocol/Protocol.js:110:16)

Am I supposed to leave the connection open until the server dies?

UPDATE: When I move the mysql.createConnection into the put request function like so:

var connection = null; 
app.put('/api/upload', function(req, res, next)
{
    connection = mysql.createConnection({
        host     : 'localhost',
        user     : 'me',
        password : 'secret',
        database : 'Database1'
    });
    connection.connect();
    doMultipleQueries(function(err)
    {
        connection.end();
    });          
};

It works fine. Does this mean connection.end() closes what mysql.createConnection created and cannot be reconnected?

Answer 3

Rather than creating and managing connections one-by-one, this module also provides built-in connection pooling using mysql.createPool(config). Read more about connection pooling.

Create a pool and use it directly:

var mysql = require('mysql');
var pool  = mysql.createPool({
  connectionLimit : 10,
  host            : 'example.org',
  user            : 'bob',
  password        : 'secret',
  database        : 'my_db'
});

pool.query('SELECT 1 + 1 AS solution', function (error, results, fields) {
  if (error) throw error;
  console.log('The solution is: ', results[0].solution);
});

This is a shortcut for the pool.getConnection() -> connection.query() -> connection.release() code flow. Using pool.getConnection() is useful to share connection state for subsequent queries. This is because two calls to pool.query() may use two different connections and run in parallel. This is the basic structure:

var mysql = require('mysql');
var pool  = mysql.createPool(...);

pool.getConnection(function(err, connection) {
  if (err) throw err; // not connected!

  // Use the connection
  connection.query('SELECT something FROM sometable', function (error, results, fields) {
    // When done with the connection, release it.
    connection.release();

    // Handle error after the release.
    if (error) throw error;

    // Don't use the connection here, it has been returned to the pool.
  });
});

If you would like to close the connection and remove it from the pool, use connection.destroy() instead. The pool will create a new connection the next time one is needed.

Connections are lazily created by the pool. If you configure the pool to allow up to 100 connections, but only ever use 5 simultaneously, only 5 connections will be made. Connections are also cycled round-robin style, with connections being taken from the top of the pool and returning to the bottom. Follow this https://github.com/mysqljs/mysql/blob/master/Readme.md#server-disconnects When a previous connection is retrieved from the pool, a ping packet is sent to the server to check if the connection is still good.

otherwise, try the below code

const mysql = require("mysql");

var connection;
function handleDisconnect() {
    connection = connection = mysql.createPool({
        host: "localhost",
        user: "xyz",
        password: "xyz",
        database: "xyz",
        multipleStatements: true,
        waitForConnections: true,
        connectionLimit: 100,
    });
    connection.getConnection(function (err) {
        if (err) {
            console.log('error when connecting to db:', err);
            setTimeout(handleDisconnect, 2000);
        }
    });
    connection.on('error', function (err) {
        console.log('db error', err);
        if (err.code === 'PROTOCOL_CONNECTION_LOST') {
            handleDisconnect();
        } else {
            throw err;
        }
    });
}

handleDisconnect();

module.exports = connection;