CODEWITHSUNDEEP
pythonmysqlwebtornado
Stiger
Stiger

Reputation: 15

In a web request handler of python tornado, should a global connection of mysql be set or not?

This is the code from a official blog example app of tornado python framework. And one problem is confusing me: A MysqlDB connection is initialized as a gloal var in this application, but if high frequency request arrived, and the connection breaks off, so the whole app is down? why not initialize a new connection in each request handler? is it a better solution? 

class Application(tornado.web.Application):
        def __init__(self):
            handlers = [
                (r"/", HomeHandler),
                (r"/archive", ArchiveHandler),
                (r"/feed", FeedHandler),
                (r"/entry/([^/]+)", EntryHandler),
                (r"/compose", ComposeHandler),
                (r"/auth/login", AuthLoginHandler),
                (r"/auth/logout", AuthLogoutHandler),
            ]
            settings = dict(
                blog_title=u"Tornado Blog",
                template_path=os.path.join(os.path.dirname(__file__), "templates"),
                static_path=os.path.join(os.path.dirname(__file__), "static"),
                ui_modules={"Entry": EntryModule},
                xsrf_cookies=True,
                cookie_secret="__TODO:_GENERATE_YOUR_OWN_RANDOM_VALUE_HERE__",
                login_url="/auth/login",
                debug=True,
            )
            tornado.web.Application.__init__(self, handlers, **settings)

            # Have one global connection to the blog DB across all handlers
            self.db = torndb.Connection(
                host=options.mysql_host, database=options.mysql_database,
                user=options.mysql_user, password=options.mysql_password)

Upvotes: 1

Views: 957

Answers (1)

A. Jesse Jiryu Davis
A. Jesse Jiryu Davis

Reputation: 24007

A single MySQL connection for the whole application is the correct design here. If there is a network error, one request will get an exception, but the MySQL connection will reconnect for the next request and your application will recover. Built-in connection pooling allows your application to have several sockets connected to MySQL in order to await several MySQL operations at once.

If you create a new MySQL connection in each request handler you'll suffer the cost of setting up a TCP socket to MySQL for each HTTP request, as well as several network round-trips to log in to MySQL. Your performance will be much, much worse. If you measure it I expect you'll see that your request latency suffers badly if you create a new MySQL connection in each request handler.

Upvotes: 1

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