[zeromq-dev] UDP performance

[Dan Goes]

First off, I never got around to thanking the list for resolving our multiple-identical-subscription notification issue. I appreciate the quick fix there, it helps a lot.

After reviewing a lot of the list's history of questions about UDP support in zeromq, I've got some of my own:

- What sort of performance increases could we see with UDP transport over TCP transport in zeromq, if it were a feature? The overall end-to-end latency between a zmq_msg_send() in one application on one host and zmq_msg_recv() in another application on the same host over the loopback interface is just too high for what we need. Initial profiling suggests that a non-negligible amount of that latency is bound up in zeromq and networking land. Is it possible to take a swing at how significant a decrease we would see in this latency by using UDP instead? I.e., are we talking an order of magnitude, or more like 5-10%? Ultimately, we'll have messages sent inter-host instead of intra-host, and our environment is not inherently lossy, but possibly congested. That is, a lot of small messages are going out frequently, but the total throughput experienced by the network is unlikely to be high. The drawbacks of UDP (packets out of order, packet loss) are acceptable for our use case, and a packet that shows up too late is better off never showing up at all.

- If UDP could help us, what options are available to have it baked into zeromq? I understand it's not enough to express interest in a feature and expect it to magically show up. Roughly speaking, where in the code would be a good place to start building this in? In terms of effort and/or time taken, can you take a really rough swing at estimating it? Thanks,

Dan
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