Low-latency, large-scale message queuing

Question

I\'m going through a bit of a re-think of large-scale multiplayer games in the age of Facebook applications and cloud computing.

Suppose I were to build something on top

Answer 1

I am building such a system now, actually.

I have done a fair amount of evaluation of several MQs, including RabbitMQ, Qpid, and ZeroMQ. The latency and throughput of any of those are more than adequate for this type of application. What is not good, however, is queue creation time in the midst of half a million queues or more. Qpid in particular degrades quite severely after a few thousand queues. To circumvent that problem, you will typically have to create your own routing mechanisms (smaller number of total queues, and consumers on those queues are getting messages that they don't have an interest in).

My current system will probably use ZeroMQ, but in a fairly limited way, inside the cluster. Connections from clients are handled with a custom sim. daemon that I built using libev and is entirely single-threaded (and is showing very good scaling -- it should be able to handle 50,000 connections on one box without any problems -- our sim. tick rate is quite low though, and there are no physics).

XML (and therefore XMPP) is very much not suited to this, as you'll peg the CPU processing XML long before you become bound on I/O, which isn't what you want. We're using Google Protocol Buffers, at the moment, and those seem well suited to our particular needs. We're also using TCP for the client connections. I have had experience using both UDP and TCP for this in the past, and as pointed out by others, UDP does have some advantage, but it's slightly more difficult to work with.

Hopefully when we're a little closer to launch, I'll be able to share more details.