How could I make asynchronous mysql operations in

问题:

I now use Python3.4 and I want to use asynchronous mysql client in Tornado. I have found torndb but after reading its source code, I think it couldn't make asynchronous mysql operations because it just encapsulates MySQLdb package.

So is there a way to make asynchronous mysql operations in Tornado?

回答1:

The canonical way to use MySQL with tornado is to use a separate set of processes to talk to MySQL and use asynchronous http requests to talk to those servers (see also answer #2 in Is Tornado really non-blocking?). These processes can be on the same machine and using tornado, or application servers somewhere else. A minimal example:

import json, sys, time
from MySQLdb import connect, cursors
from tornado import gen, httpclient, web, netutil, process, httpserver, ioloop

class BackendHandler(web.RequestHandler):   
    def get(self):
        time.sleep(1)  # simulate longer query
        cur = connect(db='tornado', user='root').cursor(cursors.DictCursor)
        cur.execute("SELECT * FROM foo")
        self.write(json.dumps(list(cur.fetchall())))

class FrontendHandler(web.RequestHandler):
    @gen.coroutine
    def get(self):
        http_client = httpclient.AsyncHTTPClient(max_clients=500)
        response = yield http_client.fetch("http://localhost:8001/foo")
        self.set_header("Content-Type", 'application/json')
        self.write(response.body)


if __name__ == "__main__":
    number_of_be_tasks = int(sys.argv[1]) if len(sys.argv) > 1 else 20
    number_of_fe_tasks = int(sys.argv[2]) if len(sys.argv) > 2 else 1
    fe_sockets = netutil.bind_sockets(8000)  # need to bind sockets
    be_sockets = netutil.bind_sockets(8001)  # before forking
    task_id = process.fork_processes(number_of_be_tasks + number_of_fe_tasks)
    if task_id < number_of_fe_tasks:
        handler_class = FrontendHandler
        sockets = fe_sockets
    else:
        handler_class = BackendHandler
        sockets = be_sockets
    httpserver.HTTPServer(web.Application([(r"/foo", handler_class)])
        ).add_sockets(sockets)
    ioloop.IOLoop.instance().start()

That said, if the main thing your web server is doing is talking to MySQL directly tornado doesn't win you much (as you'll need as many processes as you want concurrent MySQL connections). In that case a better stack might well be nginx+uwsgi+python. What tornado's really good for is talking to multiple backend servers, using HTTP, potentially in parallel.