FriendFeed, which was recently acquired by Facebook, just released an interesting piece of open source software.

Tornado is an open source version of the scalable, non-blocking web server and tools that power FriendFeed. The FriendFeed application is written using a web framework that looks a bit like web.py or Google’s webapp, but with additional tools and optimizations to take advantage of the underlying non-blocking infrastructure.

The story so far

This release generated widespread interest among the Python and open source development communities. Rightfully so. There are many reasons to like Tornado. To begin with, it’s fast — and that’s fundamental for a web server. By using nginx as a load balancer and a static file server, and running a few Tornado instances (usually one per core available on the machine) it’s possible to handle thousands upon thousands of concurrent connections on relatively modest hardware; and this isn’t just theory. Tornado has already proven its worth in the field, by allowing FriendFeed to scale graciously.

Tornado is not only a fast web server, it acts as a very lightweight application framework as well. As such, it’s an appealing alternative to well established frameworks to the growing group of developers who’d like to develop “closer to the metal” and avoid the baggage associated with full-fledged web frameworks. The two things combined make Tornado ideal for developing “real time” web services and applications.

The feedback so far hasn’t been all positive though. Criticism of the project has mainly focused on the lack of test coverage and the fact that FriendFeed has opted not to contribute to, and improve on, the existing Twisted Web project (which has similar goals). To make things worse, there were a few nonchalant comments about it as well. Performance issues and lack of ease of use were the reported motivations for starting a new project from scratch.

Dustin Sallings started working on a hybrid solution (henceforth Tornado on Twisted) that would reportedly keep the good parts that Tornado introduced, while using Twisted as its core for networking and HTTP parsing.

At this point I became naturally curious about the speed of these three web servers. Is Tornado really faster than Twisted Web? And what about Tornado on Twisted, would it be faster or slower? Let’s find out.

Benchmark results

I ran a simple Hello World app for all three web servers. All the web servers were run in standalone mode without a load balancer. I stress tested the web servers with httperf using a progressively larger amount of concurrent requests. 100,000 requests were generated for each test. The web servers were run on a desktop machine with an Intel® Core™2 Quad Processor Q6600 (8M Cache, 2.40 GHz, 1066 MHz FSB) processor and 8GB of RAM. The operating system of choice was Ubuntu 9.04 (x86_64).

Without further ado, here are the results:

As you can see Tornado turned out to be faster than the rest of the Python web servers. Handling a peak of almost 3900 req/s with a single front-end and on commodity hardware is nothing to sneer at.

Twisted Web didn’t do too bad either (max. 2703.7 req/s), but the difference in performance is noticeable. Likewise, the performance of Tornado on Twisted was virtually identical to that of Twisted Web.

There you have it. I was curious about the possible outcome and now I know. Remember, this is a report on the numbers I got on my machine, not a research paper. But I hope that you find them interesting nevertheless.

Show me the code

Tornado:

import tornado.httpserver
import tornado.ioloop
import tornado.options
import tornado.web
import logging

from tornado.options import define, options

define("port", default=8888, help="run on the given port", type=int)

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world!")

def main():
    tornado.options.parse_command_line()
    application = tornado.web.Application([
        (r"/", MainHandler),
    ])
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(options.port)
    tornado.ioloop.IOLoop.instance().start()

if __name__ == "__main__":
    main()

Twisted Web:

from twisted.internet import epollreactor
epollreactor.install()
from twisted.internet import reactor
from twisted.web import server, resource

class Simple(resource.Resource):
    isLeaf = True
    def render_GET(self, request):
        return "Hello, world!"

site = server.Site(Simple())
reactor.listenTCP(8888, site)
reactor.run()

Tornado on Twisted:

from twisted.internet import epollreactor
epollreactor.install()
from twisted.internet import reactor

import tornado.options
import tornado.twister
import tornado.web
import logging

from tornado.options import define, options

define("port", default=8888, help="run on the given port", type=int)

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world!")

def main():
    tornado.options.parse_command_line()
    application = tornado.web.Application([
        (r"/", MainHandler),
    ])

    site = tornado.twister.TornadoSite(application)
    reactor.listenTCP(options.port, site)

    reactor.run()

if __name__ == "__main__":
    main()

UPDATE (September 14, 2009):

• The original version of this post included Unicorn as well. This wasn’t fair however, since it’s not an asynchronous web server.
• EventMachine HTTP Server was added, but I have since decided to remove it as I prefer to let the article be a fair comparison between asynchronous Python web servers.
• I initially used Apache Benchmark (ab). The results were misleading at best. I re-ran the tests with httperf and updated the results above.
• Stock Tornado couldn’t be tested with httperf because their HTTP Server doesn’t implement getClientIP(). I had to manually modify a method to return the remote ip address. This may introduce a very minimal advantage for Tornado, but it should be negligible in this context.
• I modified the examples for Twisted and Tornado on Twisted, to ensure that both took advantage of the epoll-based reactor.

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